Understanding Car Engine Sensors

EVERY ENGINE SENSOR EXPLAINED - MAF, MAP, IAT, TPS, 02, NOx, EGT - How it works, location, OBD2 code

Estimated read time: 1:20

Summary

In this informative video by Driving 4 Answers, every crucial car engine sensor is thoroughly explained, including their function, mechanism, and location. The video covers 16 different engine sensors, grouped into five categories: Position, Air flow, Pressure, Temperature, and Air-fuel ratios and emissions. For each sensor type, it also discusses what happens when they go faulty, and the related onboard diagnostics (OBD2) code. To enhance understanding, the video provides timestamps for easy navigation to specific sensor discussions. This is a comprehensive guide, perfect for car enthusiasts and technicians alike, looking to deepen their knowledge on engine sensors.

Highlights

Every car engine relies on sensors to function efficiently, varieties include MAF, MAP, IAT, TPS, and more. ⚙️
Understanding the function and location of each sensor helps in diagnosing and repairing engine issues. 🔍
Faulty crankshaft sensors can prevent car starting or lead to uneven acceleration. 🚀
Modern sensors like wide-band oxygen sensors are critical for both performance and emissions tuning. 🌟
Maintenance and timely replacement of faulty sensors can prevent engine damage and ensure smooth driving. 🕵️

Key Takeaways

Engine sensors play a vital role in optimizing car performance and reducing emissions. 🚗
Different types of sensors include Position, Air flow, Pressure, Temperature, and Air-fuel ratios. 📊
Faulty sensors can lead to poor engine performance, starting issues, and increased emissions. 🔧
Modern sensors utilize advanced technology such as Hall effect, piezoelectric materials, and thermisters. 🕶️
Keeping sensors in good condition ensures longer engine life and optimal performance. 🛠️

Overview

Driving 4 Answers dives into the intriguing world of car engine sensors in this detailed video, breaking down how these vital components keep our engines running smoothly. By explaining the purpose, location, and potential malfunctions of 16 different sensors, viewers can gain a comprehensive understanding of these essential parts.

From the crankshaft position sensor, which aligns pistons precisely with engine timing, to the oxygen sensor measuring exhaust's air-fuel ratio, the video categorizes sensors into easily digestible sections. Alongside each sensor explained are symptoms of failure, helping viewers understand what might lead to rough idling or poor fuel economy.

The video not only elucidates the workings of older sensors like the vane airflow meter but also highlights the sophistication of contemporary sensors like wideband O2 and EGT sensors. For those passionate about cars, this video is a valuable resource in maintaining and optimizing engine performance and longevity.

Chapters

00:00 - 00:30: Introduction to Engine Sensors This chapter provides an introduction to various car engine sensors, detailing what each sensor does, how it operates, its location, and the implications of sensor faults. The comprehensive discussion covers 16 different sensor types, with timestamps available for quick navigation to specific sensors of interest. The emphasis is on the importance of these sensors for the proper functioning of the engine and the Engine Control Unit (ECU).
00:30 - 01:00: Overview of Sensor Categories The chapter discusses the categorization of sensors, highlighting their similar working principles despite differing functions. Sensors are divided into five categories for better understanding: Position, Air flow, Pressure, Temperature, and Air-fuel ratios, emissions, and others. The chapter begins with an explanation of position sensors, specifically the crankshaft position sensor, which informs the ECU of the crankshaft's position.
01:00 - 02:30: Crankshaft Position Sensor The chapter 'Crankshaft Position Sensor' explains the importance of knowing the crankshaft position to determine the position of the piston inside the bore, which enables the ECU to accurately initiate fuel injection and/or spark ignition. There are two main types of crankshaft position sensors: Hall effect sensors, which have three wires, and Variable Reluctance (VR) sensors, which have two wires. Despite slight differences in operation, both types of sensors function based on the principles of electromagnetism.
02:30 - 04:00: Camshaft Position Sensor The chapter titled 'Camshaft Position Sensor' explains the function of the camshaft position sensor in conjunction with a trigger wheel made from ferrous metal. The trigger wheel features one or more missing teeth. When a missing tooth passes in front of the sensor, it alters the signal sent to the ECU. The position of the missing tooth relative to the sensor is fixed to a specific position of the crankshaft. By detecting the change in signal, the ECU can determine the crankshaft's position at any given moment. The ECU is also configured to recognize the total number of teeth on the trigger wheel.
04:00 - 06:00: Throttle Position Sensor The chapter explains the role and working principle of the throttle position sensor (TPS) in an engine. It describes how the ECU (Engine Control Unit) calculates engine speed or RPM by detecting the frequency of a missing tooth on a rotating component, indicating its position. The discussion includes the positioning of the crankshaft and its relationship with the trigger wheel, which must be near each other to work effectively. The trigger wheel is essential for reading engine speed and is located on components rotating at the same speed as the crankshaft, such as the crankshaft pulley, timing gear associated with the timing belt or chain, or the flywheel.
06:00 - 08:30: Mass Air Flow (MAF) Sensor The chapter discusses the Mass Air Flow (MAF) Sensor, particularly locating the crankshaft position sensor, which might be in one of three places. A complete failure of this sensor can prevent the engine from starting or cause it to stall shortly after starting. An incomplete failure may lead to issues such as jerky acceleration, engine misfiring, rough running, poor idle, and bad fuel mileage. It is noted that the camshaft position sensor serves a similar purpose for the camshaft as the crankshaft sensor does for the crankshaft. In theory, an engine can operate with only a crankshaft sensor.
08:30 - 10:00: Airflow Meter (AFM) The chapter titled 'Airflow Meter (AFM)' discusses the role of the camshaft position sensor in engine management. It highlights how the camshaft position sensor complements the crankshaft position sensor by providing additional data to the ECU, which helps in verifying and completing the information needed for optimal engine operation. The sensor is instrumental in functions like cylinder selected knock control and sequential injection. Overall, the cam sensor operates on a similar principle as the crank sensor, ensuring precise tracking of each cylinder's activities.
10:00 - 12:30: Manifold Absolute Pressure (MAP) Sensor The chapter titled 'Manifold Absolute Pressure (MAP) Sensor' explains the function of the cam position sensor. It discusses how the sensor reads a smaller trigger wheel due to the camshaft size and is generally located near the camshaft, on the cam cover, either at the front, back, or along the axis. The chapter outlines symptoms of sensor failure, which include no-start conditions or poor engine performance, and mentions that these symptoms are similar to those of a position sensor. Additionally, the throttle position sensor's role in measuring the position of the throttle plate is briefly touched upon.
12:30 - 14:30: Oil Pressure Sensor The chapter discusses the operation of the throttle plate in relation to the throttle pedal. When the pedal is pressed, it manipulates the throttle plate at the intake manifold's entrance. Fully pressing the pedal opens the plate completely, allowing maximum airflow for maximum acceleration. The ECU monitors the throttle plate position to assess the engine's load and adjust injection and ignition timing. The chapter also touches on the function of a throttle position sensor, which uses a variable resistor to detect the plate's position.
14:30 - 16:00: Fuel Pressure Sensor The chapter on the Fuel Pressure Sensor begins with a technical explanation of how sensors work based on their electrical resistance output, which changes according to the position of a movable part. In particular, it discusses the operation of throttle position sensors, where the throttle plate shaft is directly linked to a variable resistor. This mechanical setup results in varying resistance outputs in alignment with the throttle plate's position, which are then interpreted into useful signals for the ECU by the sensor's onboard electronics. The chapter highlights that this explanation pertains to traditional throttle position sensors.
16:00 - 18:00: Intake Air Temperature (IAT) Sensor This chapter discusses the modern throttle position sensors which now rely on non-contact position measurements using technologies such as Hall effect, induction, or magnetic resistance, as opposed to the older variable resistor method. These sensors are crucial for measuring the position of the throttle plate and are typically located on the throttle body. A common symptom of a malfunctioning throttle position sensor is erratic acceleration, indicating that the car does not properly respond to the throttle pedal inputs.
18:00 - 20:30: Coolant Temperature Sensor The chapter discusses the impact of the coolant temperature sensor on vehicle performance. It explains that issues with the sensor can lead to idle problems, making it either too high or too low, and may also cause difficulties in starting the vehicle. The Engine Control Unit (ECU) uses data from this sensor, alongside other information, to determine not only the timing for fuel injection but also the appropriate amount of fuel to inject. This process requires knowledge of the air entering the engine to balance the fuel-air mixture correctly.
20:30 - 23:00: Fuel Temperature Sensor The chapter titled 'Fuel Temperature Sensor' begins by explaining the function of a Mass Air Flow (MAF) sensor within a car's engine management system, specifically telling the Engine Control Unit (ECU) how much air is entering the engine. The discussion moves into the two primary types of MAF sensors - hot wire and hot film - noting their differences and the advanced technology associated with the hot film sensor. A common operating principle for both types is highlighted, which is based on the high temperature coefficient of resistance found in metals such as platinum and tungsten. These materials' resistance changes significantly with temperature variations, making them suitable for accurate air flow measurement.
23:00 - 25:30: Oil Temperature Sensor The chapter discusses the functioning of Oil Temperature Sensors, particularly focusing on the relationship between temperature changes in metals and their resistance. It explains how increased airflow influences temperature and thus alters resistance, which the Mass Air Flow (MAF) sensor's electronics then measure. This data is converted into signals for the Engine Control Unit (ECU). The chapter notes that while this explanation covers the basic principles, the actual MAF sensor is more complex and a more detailed explanation is available in a dedicated video.
25:30 - 30:30: Oxygen (O2) Sensor The chapter provides information on the location and function of the Mass Air Flow (MAF) sensor in a vehicle. It mentions that the MAF is typically found right after the air cleaner or air filter housing, and before the throttle body. The text explains the consequences of a failing MAF sensor, highlighting that a completely failed MAF will prevent the engine from starting, while a partially failing or contaminated MAF will send incorrect data to the ECU, leading to improper fuel injection and result in a rough running engine.
30:30 - 35:00: Exhaust Gas Temperature (EGT) Sensor The chapter discusses the functionality and role of the Exhaust Gas Temperature (EGT) Sensor, explaining how it is linked to engine performance issues such as poor idle, hesitation during acceleration, and poor mileage. The chapter explains the difference between an Airflow Meter (AFM) or vane airflow meter and a Mass Airflow (MAF) sensor. It highlights that although both devices serve the same purpose of measuring the amount of air entering the engine, they operate differently. The AFM uses a flap mechanism to help gauge airflow and is typically found in older vehicles.
35:00 - 38:00: Nitrogen Oxides (NOx) Sensor The chapter discusses the Nitrogen Oxides (NOx) sensor, specifically focusing on the mechanism involving a vane or flap connected to a variable resistor. This setup is similar to the throttle position sensor, where different positions of the vane output different resistances. These resistances are read by onboard electronics, which convert them into signals used by the engine control unit (ECU) to determine the vane's position and the amount of air entering the engine. The discussion also makes a comparison to the mass airflow (MAF) sensor, noting that the airflow meter is typically located near or after the air filter.
38:00 - 41:00: Knock Sensor The chapter focuses on the knock sensor, comparing its function and failure symptoms to those of the mass airflow sensor (MAF) and the airflow meter (AFM). The knock sensor has a similar role to these sensors but measures the pressure inside the engine's intake manifold rather than the air mass directly.
41:00 - 44:30: Conclusion The conclusion chapter discusses the functionality of the MAP (Manifold Absolute Pressure) sensor. It explains how the sensor measures the air mass by calculating the pressure exerted in an enclosed space. The chapter describes how the pressure measurement indicates the amount of air entering the engine. The MAP sensor relies on a micromachined silicon chip that includes a silicon membrane and a piezoelectric material to make these measurements.

EVERY ENGINE SENSOR EXPLAINED - MAF, MAP, IAT, TPS, 02, NOx, EGT - How it works, location, OBD2 code Transcription

00:00 - 00:30 So today, we're explaining all the car engine sensors Every single one of them. And for each of them, we're going to explain: What it does. How it works. Where the sensor is located. And what happens if it goes faulty. Obviously, this is a pretty long video, with information on 16 different sensor types. So, of course, you can find timestamps for each sensor down in the description. So that you can quickly access only the sensors you're interested in. Now, although there's a lot of sensors that are needed for the engine and the ECU(or the engine control unit) to do their job properly.
00:30 - 01:00 Many of them work in pretty similar ways. They do different things, but they have very similar characteristics. And this is why to make things more logical and easier to understand I have grouped sensors into five categories. Position. Air flow Pressure Temperature. And air-fuel ratios, emissions and others. And we're starting right away with position sensors. The crankshaft position sensor tells the ECU the position of the crankshaft.
01:00 - 01:30 Because the position of the piston is fixed in relation to the position of the crankshaft. By knowing the position of the crankshaft, the ECU also knows where the piston is inside the bore. And by knowing this, it can initiate fuel injection and/or spark ignition events, at the correct time. Crankshaft position sensors are most often either Hall effect, which is three wires. Or VR(variable reluctance) which is two wires. Although they work slightly differently, both rely on the basic principles of electromagnetism,
01:30 - 02:00 to read a trigger wheel made from a ferrous metal. The trigger wheel is going to have one or more teeth missing. And whenever a missing tooth passes in front of the sensor, it's going to change the signal that the sensor sends to the ECU. Now, the position of the missing tooth in relation to the sensor, is going to be fixed to a certain position of the crankshaft. And by seeing the change in the signal, the ECU can tell exactly where the crank is at that moment in time. Now the ECU is also configured to the total number of teeth on the trigger wheel.
02:00 - 02:30 And by knowing the total number of teeth, and measuring how often the missing tooth passes in front of the sensor, the ECU can calculate engine speed or RPM. Now, every car engine has one crankshaft, and thus it only needs one crankshaft position sensor. The crankshaft position sensor in order to read the trigger wheel must be located very near it. And the trigger wheel must be installed on something that rotates at the same speed as a crankshaft. And it's usually either the crankshaft pulley, the timing gear where the timing belt or timing chain attaches, or the flywheel.
02:30 - 03:00 So, one of these three locations is where you're going to find your crankshaft position sensor. If the sensor fails completely, then the engine will not start. Or it will start but stall after running very briefly. If the failure is not complete, then you may get jerky or uneven acceleration, engine misfiring, rough running, poor idle, bad mileage, and so on. Now, the camshaft position sensor does the same thing as the crankshaft position sensor. But for the camshaft. Now, in theory the engine can run with a crank sensor alone.
03:00 - 03:30 But adding a camshaft position sensor paints a much more complete picture for the ECU. And it's also a layer of verification for the information coming from the crankshaft position sensor. Now, a camshaft position sensor lets the ECU know, what each cylinder is doing and when is it doing it. And this is why it can be used for, for example, cylinder selected knock control, sequential injection. And other cylinder selective systems. The cam sensor works on the same principle as the crank sensor.
03:30 - 04:00 The only difference is, that it reads a much smaller trigger wheel with fewer teeth, due to the size of the camshaft. To read the position of the camshaft, the cam position sensor must be near it. Usually, you're going to find it somewhere on the cam cover. Either at the front or at the back of the camshaft. Or less often somewhere along the axis of the camshaft. Failure symptoms are usually the same or very similar to a position sensor. Either a no-start condition, or poor engine running. The throttle position sensor measures the position of the throttle plate.
04:00 - 04:30 When you're operating the throttle pedal, you're actually operating the throttle plate that's usually at the entrance of the intake manifold. When you floor it, the throttle plate gets fully opened, allowing maximum air into the engine, for maximum acceleration. By knowing the position of the throttle plate, the ECU can know the load placed on the engine. And can thus vary injection and ignition timing accordingly. A throttle position sensor works by relying on a variable resistor. A variable resistor is essentially an electrical component,
04:30 - 05:00 which changes its electrical resistance output based on its position. It contains a movable part. And different positions of this movable part will have different resistance output. In case of the throttle position sensor, the throttle plate shaft is connected directly to the variable resistor. So different positions of the throttle plate will have different resistance outputs. Which are then measured and converted into a useful signal for the ECU, by the onboard electronics of the throttle position sensors. Now, this is what old throttle position sensors used to work with.
05:00 - 05:30 But today, modern throttle position sensors, actually rely on non-contact position measurements. And either use Hall effect, induction or magnetic resistance to do the same job as a variable resistor. Obviously, to measure the position of the throttle plate, the throttle position sensor must be located on the throttle body itself. And this is where you always the throttle position sensor. One of the most obvious symptoms of a failed throttle position sensor, is going to be unpredictable acceleration. The car is going to feel as though it's not correctly responding to throttle pedal inputs.
05:30 - 06:00 Also the idle will often be affected. And it will either be too high or too low And there also might be difficulty starting the vehicle. In addition to knowing the position of the piston, so that it can know when to inject the fuel, the ECU must also know how much fuel to inject. And to know how much fuel to inject, it must know how much air is coming into the engine, so that it can inject a corresponding amount of fuel.
06:00 - 06:30 And this is exactly what a MAF(or mass air flow) sensor does for the ECU. It tells the ECU how much air is coming into the engine. Now, most MAF sensors are either hot wire or hot film. Now, they are bit different And the hot film sensor is a bit more advanced. But they both rely on the same basic principle, of the very high temperature coefficient of resistance of certain metals, such as platinum or tungsten. The very high temperature coefficient of resistance of these metals, means that even
06:30 - 07:00 very minute changes in the temperature of these metals, will change their resistance. So when air flows over these metals, it changes their temperature. The more air flows over, the more the resistance changes. And the onboard electronics of the MAF sensor measure this, and then convert the signal into useful data for the ECU. Now, obviously this is just a basic working principle. And a MAF sensor is more complicated and more interesting than this. But I do have a video that goes into great detail when it comes to MAF sensors.
07:00 - 07:30 And you can find it in the description below, and in the suggested videos in the top right corner. You will usually find a MAF right after the air cleaner housing, the air filter housing. If it's not there, it's going to be somewhere after the air filter housing, but before the throttle body. If a MAF fails completely, the engine will not start. If it's only starting to fail, or if it's a bit contaminated by dirt, then it's going to send the wrong information to the ECU. So the ECU will be injecting the wrong amount of fuel. And you can expect a rough running engine.
07:30 - 08:00 A poor idle, hesitation during acceleration, the engine stumbling, poor mileage. And other similar symptoms. Now, an AFM, or airflow meter, or vane airflow meter as it's also known, does the same thing as a MAF. It measures how much air is coming into the engine. It just does it differently, and it's usually present on older vehicles. The airflow meter has a flap or a vane inside it. And the incoming air pushes against this flap. The more air is coming in, the more it will push against and open the flap.
08:00 - 08:30 Now, the vane or flap is connected to a variable resistor, just like the throttle blade shaft of the throttle position sensor. Different vane positions are going to output the resistances. And then the onboard electronics are going to measure this, and convert it into a useful signal for the ECU. So the different resistance outputs will tell the ECU how much the vane is open, and how much air is coming into the engine. Just like the MAF sensor, the airflow meter is always going to be somewhere near or right after the air filter.
08:30 - 09:00 Since it's doing pretty much the same thing as a mass airflow sensor, the failure symptoms of an airflow meter are going to be similar or the same as with a mass airflow sensor. Just like the MAF or the AFM, the MAP(manifold absolute pressure) sensor measures how much air is coming into the engine. But unlike the AFM or the MAF , it does not measure the incoming air mass directly. Instead, it measures pressure inside the engine's intake manifold,
09:00 - 09:30 and calculates the air mass based on that. The logic is that the more air there is in an encode space, the greater the pressure that air is going to exert onto the walls of that cold space. And this is exactly what the MAP is using And by measuring the pressure, it can calculate how much air is coming into the engine. The MAP sensor measures intake air pressure, by relying on a tiny micromachined silicon chip. The silicone chip consists of a silicon membrane, and a tiny piezoelectric material.
09:30 - 10:00 The piezoelectric material reacts to the flexing of the silicon membrane, under pressure, by changing its electrical charge. The more the pressure there is, the more the silicon membrane flexes, the more the charge changes. And the onboard electronics measure this, and then convert it into a useful signal for the ECU. Now, if you're building a performance engine or significantly increasing the boost levels of your engine, then the stock MAP sensor will no longer be adequate and will need to be upgraded.
10:00 - 10:30 Now, AEM carries a whole range of robust, reliable, and accurate MAP sensors to suit all needs. If you need them, check'em out below Because the MAP must measure pressure directly in the intake manifold, it's also always located somewhere on the intake manifold. And again, because it's ultimately trying to measure the incoming air mass, failure symptoms are going to be similar or the same as with a MAF or AFM. The oil pressure sensor obviously measures oil pressure inside the engine.
10:30 - 11:00 It's a very simple, but perhaps one of the most important and vital sensors for the engine. Because without enough oil pressure, the engine is going to sustain catastrophic damage very quickly Just like many other pressure sensors on a car, the oil pressure sensor is basically a piezoresistive pressure transducer. Meaning that it works on pretty much the same basic principle as the MAP sensor we just covered. It's simply calibrated for the different values expected from the engine's oil pressure. Now in some cases, the oil pressure sensor of an engine is not a sensor at all.
11:00 - 11:30 It's just a switch. And the most basic version contains a diaphragm. Which when it flexes, it simply causes an electric circuit, and reports that there is sufficient oil pressure. If there isn't enough oil pressure, the diaphragm isn't going to flex enough. It won't be able to cause the electric circuit. And an oil pressure light is going to illuminate, warning the driver that the engine should be shut down to prevent damage. The oil pressure sensor is usually located somewhere on the engine block, often near the oil filter.
11:30 - 12:00 But it can be anywhere on the engine block, where it can be tapped directly into an engine oil passage, so that it can accurately read the oil pressure. A lack of oil pressure is one of the single most dangerous situations for an engine. So if the oil pressure sensor is malfunctioning and falsely reporting whole oil pressure to the ECU, then the ECU will falsely trigger a limp home mode, or will refuse to start the engine. Obviously, the fuel pressure sensor measures fuel pressure. That's what it does. So why is it important to measure fuel pressure?
12:00 - 12:30 Well by knowing the fuel pressure of the fuel inside the fuel rail, the ECU can know how long to open the injectors, in order to ensure that the correct amount of fuel is injected into the engine. In order to measure fuel pressure right inside the fuel rail, the fuel pressure sensor is almost always located somewhere directly on the fuel rail. Usually, the first symptom of failure is difficulty starting. Especially on a cold engine. Other symptoms include poor acceleration and poor mileage.
12:30 - 13:00 Now the IAT sensor (or the intake air temperature sensor) Obviously measures the temperature of the intake air. Now, it's important to do this, because air density is influenced by air temperature. The hotter the air, the less dense it's going to be, and the less molecules of air are going to be in a given space. Although in theory, an engine could run without an air intake sensor, it's still a very good idea to have one. And the engine's going to run better with it, than without it. The IAT sensor works together with the MAF, MAP, or AFM
13:00 - 13:30 to give the ECU a more complete picture of the air coming into the engine. Which helps reduce emissions and improve power and efficiency. Just like almost all the other temperature sensors in a car, the IAT sensor is a thermister. Meaning that its electrical resistance is going to change, in response to the changes in its temperature. And then as usual, the resistance is measured and converted into a useful signal for the ECU. The IAT sensor is often integrated into the MAF or the AFM. If it's not there, you can usually find it somewhere in the intake duct.
13:30 - 14:00 Usually near the throttle body. If you're building a performance or racing engine, and you need to add an intake air temperature sensor, then AEM has the right one for you. It's easy to install And it's reliable and accurate. As always, links are down below. If there's only a bit of dirt on the IAT sensor, then malfunction symptoms are going to be very mild and barely noticeable. If the fault is more severe, then the engine may run rough, stumble, or even stall. Or it can have very mild, short surges of power. All the remaining temperature sensors we're going to cover are also thermisters,
14:00 - 14:30 so we won't be individually explaining how each one of them works. We'll just talk but they do where they are and so on. So let's proceed with the coolant temperature sensor. Now, the coolant temperature sensor is very important for the ECU Because it tells it how warm the engine is. This is important because a cold engine needs a different amount of fuel, when compared to a hot engine. The coolant temperature sensor is also needed to trigger various actions. Such as for example starting the radiator fans Or if the engine is overheating, it can tell the ECU to trigger limp home mode.
14:30 - 15:00 Or refuse to start the engine, until it cools back down. Like almost all the other temperature sensors, the coolant temp sensor must come into direct contact with the fluid whose temperature it's trying to measure. As such we are very often going to find the coolant temp sensor at or near the thermostat. Some cars have more than one, and you can find them anywhere on the coolant piping, or wherever else coolant is passing through. A cold engine needs more fuel than a hot engine. This means that if the coolant temperature sensor is malfunctioning, and telling the ECU that the engine is cold, even though it's hot. The ECU is going to inject extra fuel, which is going to result in a rich running condition.
15:00 - 15:30 And this means you're going to get poor mileage, or even black smoke from the exhaust in severe cases. An opposite scenario is also possible, and the ECU can think that the engine is hot, even though it's cold. In that case, it's going to inject too little fuel. Which is going to lead to a lean running condition. And this can lead to the engine misfiring, or even knocking, until it heats up. Fuel temperature must be measured because fuel density, just like the density of air, is affected by temperature. Hot fuel is less dense and burns more easily,
15:30 - 16:00 so a bit more of it must be injected to compensate for this. The fuel temperature sensor is most often located somewhere at the fuel tank. Often as part of the fuel pump assembly. Less often it can be found somewhere else along the fuel lines. The information coming from the fuel temperature sensor is only used to further improve the injection accuracy, in order to meet stringent emission standards. An engine can run pretty well with a faulty fuel temperature sensor, and in some cases symptoms might not be noticeable at all. If the fault is more severe or if the sensor component fails,
16:00 - 16:30 then the vehicle might fail in emissions test. Or get slightly worse mileage and performance than usual. Automatic cars only have an oil pressure sensor, and do not measure oil temperature Measuring oil temperature can be a useful additional layer of protection. If the oil overheats, this is going to negatively impact its viscosity, and the oil won't be capable of doing its job, which can lead to engine failure. Now the ECU, by seeing the oil temperature, can activate the limp home mode, or refuse to start the engine, before oil temperature normalize again.
16:30 - 17:00 In addition to relaying information to the ECU, the oil temperature sensor can also relay information to engage, or display visible to the driver. And then the driver can take preemptive action, and shut the engine down if oil temperatures get too high. In order to be able to measure the temperatures of oil, the sensor must come into direct contact with the oil inside the engine. As such it's often found on the engine block, or less often on the cylinder head. In newer cars, it can be found integrated into the oil level sensor. Depending on how it fails, a malfunctioning oil temperature
17:00 - 17:30 sensor might make the ECU think that the oil temperatures are too high. Even though they aren't. And then the ECU might incorrectly trigger a limp home mode. The sensor can also malfunction in a way that it fails to report overly high oil temperatures, which can result in engine damage. A faulty oil temperature sensor is very easy to spot, if there's a gauge or display for it. The O2 or the oxygen sensor measures the amount of oxygen present in the exhaust gases. The amount of oxygen present in exhaust gases,
17:30 - 18:00 directly corresponds to the amount of fuel burned inside the combustion chamber. By measuring the oxygen, the oxygen sensor can actually tell the ECU the air-fuel ratio at which the engine is running. Now, the air-fuel ratio, or the ratio of air to fuel inside the combustion chamber, is absolutely critical for both engine performance and emissions. And must be constantly monitored to ensure that it is where it needs to be. We have two kinds of oxygen sensors. Narrowband and wideband. Narrowband sensors can tell if the engine is running rich or lean.
18:00 - 18:30 But they cannot tell exactly, how rich or how lean the engine is running. On the other hand, the wide band sensor covers a much wider range of air-fuel ratios. And you can tell the ECU exactly how rich or lean the engine is running. Although it's small, the oxygen sensor is a pretty complicated device. It involves zirconium bulbs, and various platings and what not. And explaining it in this video would really make the video too long and complicated.
18:30 - 19:00 So, for the purposes of this video what I will tell you, is that the amount of oxygen measured at the sensor tip, corresponds to a voltage produced by the sensor. So for example, 0.5 volts is going to be near the ideal air-fuel ratios. And at the other far ends of the spectrum, we can find too rich and too lean. So what the ECU is going to do, it's going to increase or decrease the amount of fuel injected, in order to reach again the ideal air-fuel targeted ratio. Now, most catalytic converter equipped cars, are going to have a minimum of two oxygen sensors.
19:00 - 19:30 One is going to be before, and one after the catalytic converter. The one before the catalytic converter is called the upstream oxygen sensor, and it's usually going to be right at the exhaust manifold, or right behind it. And it's used to see the exact air-fuel ratio at which the engine is running. The one after the catalytic converter, that sensor is called the downstream sensor. And it's used to verify that the catalytic converter is properly doing its job. Failure symptoms can range from barely noticeable, to very noticeable. But even if the symptoms are hard to notice, the vehicle is likely going to fail an emissions test.
19:30 - 20:00 Now, if it's noticeable, it's going to be really noticeable. The engine is going to run rough Especially on more modern cars, which rely more heavily on the oxygen sensor. More modern cars, can even refuse to start the engine if the sensor has completely failed. If you know that you have a bad oxygen sensor, then it's a really good idea to replace it as soon as possible, even if the vehicle is running okay. Because an overly rich running condition, can lead to your catalytic converter
20:00 - 20:30 failing far more sooner than it needs to. Now, wide-band oxygen sensors are also an absolutely critical tool for tuning performance and racing engines. And the AEM carries one of the most popular, and the fastest responding, wideband setup on the market. Links are below. An EGT is an exhaust gas temperature sensor. And as the name reveals, it measures the temperature of the exhaust gas. Now, an EGT is a probe that must be present directly in the exhaust stream, in order to measure the temperature of the exhaust gas.
20:30 - 21:00 By measuring the temperature of the exhaust, we can infer information about the air-fuel ratio. Because changes in the air-fuel ratio, are also going to be directly correlated with changes in the exhaust gas temperature. Now, an EGT probe isn't often used on gasoline engines. But it can be useful to protect the turbo, and the catalytic converter from thermal overall. Now, EGT probes are often used on turbo diesel and diesel engines to verify that the DPF(or diesel particular filter) has reached a
21:00 - 21:30 sufficiently high temperature for regeneration. They're also useful for protecting the SCR(or selective catalyst reduction) in LNT(or lean NOx trap) and other NOx absorbing systems. Although it's considered an old tool when it comes to tuning performance and racing engines, an EGT probe can still be a very useful tool that provides valuable insight into what's happening inside the engine. Naturally, AEM has some very sleek EGT setups, that you can check out. In order to get the most accurate reading of exhaust gas temperatures,
21:30 - 22:00 the EGT probe must be as close to the exhaust valves as possible. This is why you're always going to find it in the exhaust manifold very close to the cylinder head. The other location is always going to be after the DPF, or diesel particular filter, to verify if the DPF is doing its job. EGT probes are very rarely present from the factory gasoline engines, so really aren't any very common symptoms to discuss. When it comes to diesel vehicles. An EGT failure is going to cause the vehicle to go into regeneration mode very often. And regeneration mode is going to last longer than usual.
22:00 - 22:30 And you may also get poor mileage and poor performance. Now, NOx are nitrogen oxide sensors. And they measure the amount of nitrogen oxides in the exhaust gases. They're usually only present on diesel vehicles, and were briefly present on some stratified charged gasoline engines in the past. Their main role is to verify the correct operation of the SCR. Or the selective catalyst reduction system. This is an active emission system in diesel vehicles, which injects ammonia or diesel emissions fluid, directly into the exhaust gases.
22:30 - 23:00 And this converts the nitrogen oxides into nitrogen, water and minute amounts of CO2. There's usually two of these sensors in a diesel vehicle One before, and one after the selective catalyst reduction system. The one before, measures how much much nitrogen is coming in. And the one after measures how much nitrogen oxide is coming out, to make sure that the selective catalyst reduction system is doing its job. A failure is going to trigger most modern diesel vehicles to go into a "limp mode home". You also might get an erratic idle, and poor mileage.
23:00 - 23:30 Now 'knock' is abnormal combustion inside the engine. If it's strong enough, and if it persists long enough, it can cause catastrophic engine damage. A knock sensor is essentially a microphone. Tuned to listen to the specific frequency of knock inside the engine. This depends on the engine, but largely it actually depends on the bore and stroke of that engine. If the knock sensor detects knock, it's going to relay this information to the ECU. And the ECU is going to respond, by either retarding ignition timing,
23:30 - 24:00 or increasing the amount of fuel injected into the engine. To prevent the knock from occurring again. In order to be capable of hearing the knock resonating throughout the engine block, the knock sensor is always going to be on the engine block. Many engines with six or more cylinders have two or even knock sensors in some cases. In many cases, a knock sensor's failure will have zero effect on the way the engine is running. You might get a check engine light, but the engine will run completely normal. Now, the scenario is a bit different on more modern cars, whose ECU once it detects knock
24:00 - 24:30 sensor failure, is going to often trigger a limp home mode, until the knock sensor is replaced.
24:30 - 25:00 And there you have it.
25:00 - 25:30 All the sensors.
25:30 - 26:00 Is it really all the sensors? Well, likely not Because the number of sensors on modern engines is growing everyday.
26:00 - 26:30 And by the time I was shooting this video, somebody might have invented something new. So if I did miss a sensor, let me know. Also, if you want a more in-depth video on any of the sensors in this video, tell me about that as well. So yeah, that's pretty much it for today. As always thanks a lot for watching. And I'll be seeing you soon, with more fun and useful stuff. On the D4A channel.