Car Sensor: Checking engine sensors are largely similar to each other, despite the fact that these devices measure various physical quantities and values. To test most of them, an electronic multimeter is used, capable of measuring the value of electrical resistance and voltage.
However, most sensors can be checked by other methods, depending on the principle of their operation. Before checking the sensors, it is necessary to dismantle them from their seat, because in most cases verification directly on the spot is impossible.
Consider the purpose and methods of checking the main sensors under the hood of any modern car. Since, if at least one of them fails, the operation of the entire engine will be disrupted.
Mass airflow sensor
As the name implies, abbreviated as DFID, measures the volumetric amount of air intake by the engine. The unit of measure, in this case, is kilograms per hour. For most machines, this sensor is mounted on the air filter housing or on the intake manifold. Its device is simple, so it crashes quite rarely. However, in some cases, it can capture and issue incorrect information.
For example, when the readings are overestimated by 10 … 20%, problems arise in the operation of the engine, in particular, they can “float” at idle speed, the motor “chokes” and does not start well. If the values of the readings from the sensor are lower than they actually are, then the dynamic characteristics of the machine fall (it does not accelerate, it goes slightly uphill), and fuel consumption also increases.
The correct operation of the mass air flow sensor is very dependent on the state of the air filter. So, if the latter is very clogged, then there is a risk of trash elements – grains of sand, dirt, moisture and so on, which is very harmful to it, and leads to the fact that the sensor gives incorrect information. This can also happen if a zero resistance filter is installed on the machine (or there is simply no filter).
An interesting feature of the mass air flow sensor is that machines equipped with it cannot be tuned, increasing the power of the motor. In particular, this applies to VAZ engines, which some motorists “swing” to a power value of 150 … 160 horsepower. In this case, the sensor will obviously not work correctly, since it is simply not designed for such an amount of air flowing into the engine.
For standard VAZ engines, the mass air flow sensor at idle should record the passage of about 8 … 10 kilograms of air per hour. With an increase in speed to a value of 3000 rpm, the corresponding value increases to 28 … 32 kg / h. For engines similar in volume to VAZ engines, these values will be close or similar.
Checking the mass air flow sensor consists in measuring the DC voltage it emits using an electronic multimeter.
Throttle position sensor
The sensor is designed to fix the position of the throttle at a particular point in time. The corresponding position changes depending on whether the accelerator pedal is depressed and how much. Typically, the throttle position sensor is mounted directly on the throttle and/or on the same axis as the throttle. It is noted that if an original high-quality sensor is installed on the machine, then there will most likely be no problems in its operation. However, there are many fake low-quality sensors on sale (for example, Chinese-made), which, firstly, do not last long (about a month), and secondly, provide incorrect information, which leads to engine operation in conditions that are not optimal for it.
For example, with a partial output of the throttle position sensor, problems arise in the reaction of the machine to the actions of the driver with respect to the gas pedal. For example, dips appear when you press it, spontaneous increase in speed, their “swimming”. Also, in case of a malfunction of the throttle position, jerks and dips during engine operation under load are possible. In a word, the accelerator pedal “begins to live its own life”.
There are cases when the TPSs failed due to the fact that they were damaged in a car wash with a powerful water jet. Up to the point that they can simply be knocked down from their seat. Therefore, you need to carefully monitor this when performing a car wash on your own or in a specialized institution. In general, the throttle position sensor is a fairly reliable device. However, when it fails, it cannot be repaired, so it should only be replaced completely.
You can check the throttle sensor with a multimeter that can measure DC voltage in the range up to 5 Volts.
Coolant temperature sensor
It has other names – temperature sensor, coolant sensor. As the name implies, its task is to fix the temperature of antifreeze or antifreeze, and transmit this information to the electronic engine control unit (ECU). Based on the information received, the control unit corrects the enrichment of the air-fuel mass entering the engine, respectively, the colder the engine – the more rich this mixture will be. The coolant temperature sensor is most often located on the exhaust pipe of the cylinder head (although there may be other options, it depends on the specific car model).
In fact, this sensor is a thermistor – that is, a resistor that changes its internal electrical resistance depending on the temperature of its control element. The lower the temperature, the higher the resistance, and vice versa, the higher the temperature, the lower the resistance. However, the sensor supplies the computer with a voltage value, not resistance. This is implemented by the sensor control system when a 5-volt signal is supplied to it through a resistor with a constant resistance, which is located inside the control controller. Therefore, together with the resistance, the output voltage also changes. So, if the antifreeze temperature is low, the output voltage will be large, and as it warms up, the voltage will decrease.
Signs of sensor failure:
Spontaneous inclusion of the cooling fan with a cold engine; not turning on the cooling fan when the engine is hot (at extreme temperatures, when it should turn on); problems starting the engine “hot”; increased fuel consumption.
In fairness, it is worth noting that the sensor device is quite simple, and there’s simply nothing to break there. However, in some cases (for example, due to mechanical damage or from old age), electrical contact inside the sensor may be damaged. The second possible cause of failure is a break in the wiring from the sensor to the computer or damage to its insulation. As in the case with other sensors, this unit cannot be repaired, and it only needs to be replaced with a new one.
Checking the coolant temperature sensor can be done either directly at its seat in the engine or by dismantling it first.
Knock sensor (abbreviated DD) detects the appearance in the engine directly of detonation knocks. Typically, the knock sensor is mounted directly on the engine block, most often between the second and third cylinders. Currently, there are two types of such sensors – resonant and broadband. The first of them (resonant) are considered obsolete, and they can only be found in engines of old designs. The resonance sensor is designed for a specific sound frequency, which corresponds to microexplosions in the motor. A broadband sensor detects sound waves in the range from 6 Hz to 15 kHz. The relevant information is transmitted to the electronic control unit, and already the control unit decides whether detonation is taking place or not. And if it does exist, then the computer automatically shifts the ignition angle to avoid a repetition of it.
Signs of failure of the knock sensor are the following factors:
- loss of dynamic characteristics of the machine (it does not accelerate, pulls poorly uphill);
- idle speed “float”, they can also be unstable in the operating mode;
- increase fuel consumption.
- The knock sensor can be checked by two methods – by measuring the value of the output resistance, voltage, or using the oscilloscope to watch the mode of its operation in dynamics.
Another name for the sensor is a lambda probe. The main task of the unit is to fix the amount of oxygen in the exhaust gases. As a rule, it is installed near the catalyst or on the exhaust pipe of the muffler. In some car models, the design provides for the use of two oxygen sensors – one before the catalyst, and the second after. The relevant information is traditionally transmitted to the electronic control unit, and it already makes a decision on the fuel supply to the engine, adjusting the composition of the air-fuel mixture (poor/rich). If oxygen is detected in the exhaust gas, then the mixture is poor, if not detected, it is rich.
The oxygen sensor itself is quite reliable, and rarely fails. However, if this happens, then the emission of harmful substances along with exhaust gases into the atmosphere increases. Externally, the failure of the lambda probe can be determined by the increased fuel consumption. A conditional disadvantage of the sensor is its relatively high price compared to other car sensors.
The oxygen sensor is checked both by visual method and by a tester. The method of voltage measurement and signal supply will depend on how many contact specific lambda is taken.
Crankshaft position sensor
Its abbreviated name is DPKV. This is one of the main sensors of the internal combustion engine, and all its work depends on it. The task is to generate an electrical signal about a change in the angular position of a special gear disk fixed to the crankshaft. Based on this information, the electronic engine control unit decides at what time in which cylinder to supply fuel and light a candle. Typically, the crankshaft position sensor is mounted on the cover of the oil pump. Structurally, the device is very similar to a conventional magnet with a thin wire.
If the DPKV sensor fails, two situations may occur. The first is that the engine completely stops working, because the synchronization of fuel supply, sparks and so on is lost. This happens most often. However, in some cases, the electronic control unit puts the engine in emergency mode, in which the engine speed is limited to 3000 … 5000 rpm. At the same time, a Check Engine warning light is activated on the dashboard.
Checking the crankshaft position sensor is performed by three methods: resistance, inductance and an oscilloscope are measured.
It is located on the gearbox and fixes the shaft rotation speed, transmitting relevant information to the electronic control unit. And the computer already calculates the speed based on the information received. In cars with a manual transmission, the relevant information is transmitted to the speedometer located on the dashboard. In machines equipped with automatic transmission, on the basis of information including from it (but not only), but a decision is also made to shift gears to increase or decrease. Also, based on the information from the speed sensor, the car’s mileage is calculated, that is, the odometer is running.
The sensor provides voltage pulses to the electronic control unit in the range from 1 to 5 Volts with a frequency proportional to the speed of rotation of the wheels. By their frequency, the device calculates the speed of the machine, and by the number of pulses – the distance traveled.
The sensor itself is a fairly reliable device, however, in some cases, the plastic gear wears out, its contacts may oxidize, which leads to ECU problems. In particular, the control unit cannot understand whether the car is standing or driving, and at what speed. Accordingly, this leads to problems in the operation of the speedometer, as well as gear changes in automatic transmission. Also, when the sensor fails (contact oxidation), lower idle speeds are noted, with sharp braking, the engine speed “sags” strongly, the dynamic characteristics of the machine decrease (it slightly accelerates, does not pull). On some vehicles (for example, on some Chevrolet models), the electronic control unit in emergency mode shuts off the engine, and movement becomes impossible.
Checking the speed sensor requires using one of the three available methods.
Camshaft position sensor
Similarly, DPCV, the camshaft position sensor (abbreviated DPRV) reads information about the angle of its position and transfers the corresponding information to the computer. Based on the information received, the control unit decides to open the fuel nozzles at a certain point in time. On the old injection engines (until about 2005), the camshaft position sensor was not installed. Because of this, fuel injection into the intake manifold on such engines was carried out in pairwise-parallel mode, in which two nozzles open simultaneously, which is characterized by excessive fuel consumption.
On the engines on which the DPRV is installed, the so-called phased fuel injection is performed. That is, only one injector nozzle opens, where fuel should be supplied at the moment. As for the location of the sensor, on eight-valve engines it is mounted at the end of the cylinder head. On sixteen-valve power units, this sensor is also usually located on the cylinder head, near the first cylinder.
When the camshaft position sensor fails, the electronic control unit puts the engine into emergency mode, in which the nozzles operate in pair-parallel mode, opening simultaneously. This leads to an excessive consumption of fuel by 10 … 15%, in some cases the engine “troit”. Usually, an error signal is generated in the computer, and the Check Engine warning light is activated on the dashboard. Therefore, additional diagnostics must be performed using the electronic error scanner.
Checking the LPR sensor can be done using a multimeter and/or oscilloscope.
As the name implies, this node is the key to the anti-lock system (abbreviated as ABS). On machines equipped with this system, there is one such sensor on each wheel. Their task is to fix the speed of rotation of the wheel at a particular point in time. The location method for the machines may be different, however, in any case, the sensor will be located in close proximity to the rim, in the vicinity of the hub. Usually, signal wires go to it, by which it is possible to determine the exact location of the sensors on the front and far wheels.
As a rule, the sensors themselves are quite reliable, and rarely fail, except due to mechanical damage associated with the fact that they are installed in close proximity to the wheel and the road. More often, the wiring going to / from them is damaged. It may fray or the insulation will be damaged on the wires. If the electronic control unit “sees” that incorrect information is coming from the sensor / sensors, it activates the Check Engine warning light on the dashboard, and the ABS system simply turns off in emergency mode. Naturally, this leads to a decrease in driving safety.
The ABS sensor is checked in various ways – by measuring resistance, voltage, or using an oscilloscope (the most advanced method). On newer machines, Hall effect sensors are installed as ABS sensors.
Sensors whose operation is based on the Hall effect (why they are called so) are used in electronic ignition systems. Their application provides two main advantages – the absence of a contact group (a problem node that can sometimes burn), as well as providing a higher voltage on the spark plug (30 kV instead of 15 kV). However, similar sensors are also used in other systems of modern cars – brake, anti-lock, in the operation of the tachometer. However, the principle of verification is almost the same for them and consists of measuring the resistance and/or voltage on the sensor with an electronic multimeter.
If the Hall sensor located in the electronic ignition system fails, the following external signs of this failure occur:
problems with starting the engine up to the complete inability to start it;
problems in the engine idling (interruptions, unstable engine speeds appear); twitching of the car when driving in a mode when the engine has gained high speed; the engine stalls while the machine is moving.
The Hall sensor is a fairly simple and reliable device, but in some cases, it can “lie”, that is, produce incorrect data. If, as a result of the check, it turns out that the sensor has completely or partially failed, then it is unlikely to be repaired (and there is no point in this), therefore, it is necessary to replace it. The sensor in the ignition system of the carburetor car is located in the distributor.
Checking the Hall sensor in the ignition system can be done in one of four ways.
Oil pressure sensor
There are two types of oil pressure sensors (or DDM for short) – mechanical (considered obsolete and installed, respectively, on old cars) and electronic (modern, installed on most modern cars). Regardless of its type of DDM, the position of the oil pressure sensor is usually located in the oil filter area in the engine compartment.
Oil pressure sensors are fairly reliable devices (although a mechanical one breaks down more often, because its design has moving electrical contacts that fail over time), but there are malfunctions in their wiring (wire breakage, insulation damage). Signs of failure of the sensor will be problems with the indication of pressure and / or oil level in the engine.
Please note that if problems arise in the operation of the oil pressure sensor, the diagnostics should be performed as quickly as possible, since a low level of lubricating fluid in the crankcase is a critical indicator, and it must always be kept at a normal value constantly!
Checking the oil pressure sensor is only possible when dismantling from the seat. To check the motorist will need an electronic multimeter (it can be replaced by a control lamp) and an air compressor.
Fuel pressure sensor
The fuel pressure sensor is designed directly so that the ECU, in fact, receives information about the value of this pressure. These devices install both gasoline engines equipped with injectors and modern diesel engines with the Common Rail fuel system. These sensors are installed in the fuel rail of the engine. In gasoline and diesel engines, the task of the fuel pressure sensor is the same, and consists in providing a pressure value in a certain framework necessary for the normal functioning of the motor, ensuring its rated power, and normalizing noise during its operation. Some systems provide for the installation of two sensors – in high and low pressure systems.
Structurally, the sensor is a sensor element consisting of a metal membrane and strain gauges. The thicker the membrane, the more pressure the sensor is designed for. The task of strain gages is to convert the mechanical bending of the membrane into an electrical signal. The output voltage value is about 0 … 80 mV.
If the pressure value is outside the specified limits (these values are stored in the memory of the electronic control unit), the control valve in the fuel rail is activated in the system and the pressure is adjusted accordingly. In the event of a sensor failure, the computer activates the Check Engine warning light on the dashboard and starts using standard (unregulated) fuel consumption values. This leads to the non-optimal operation of the engine, which is reflected in the excessive consumption of fuel and loss of engine power (dynamic characteristics of the machine).
Information about checking the fuel pressure regulator you can read separately.
Absolute pressure sensor
In the classic version, the absolute air pressure sensor (DBP) is made of four resistors with a variable resistance value, and which are connected by an electronic bridge. They are glued to a diaphragm, which is either compressed or stretched depending on what pressure of the incoming air is currently at the intake manifold. The task of the DBP is to record the change in pressure at the inlet pipe depending on the change in load and engine speed, converting this information into an output electrical signal. This signal is traditionally fed to the electronic control unit, and based on this information, the computer changes the duration of the fuel supply to the combustion chambers, as well as the ignition timing.
As a rule, the air pressure sensor is located on the intake air tract (depending on the design of a particular car). When it fails, problems begin in the engine – idle speed “floats”, the car loses dynamic characteristics, fuel consumption increases. If the sensor is damaged, it must be replaced with a new one.
The operation of the phase sensor is based on the aforementioned Hall effect. Its task is to fix the so-called top dead center compression of the piston of the first cylinder. The relevant information is transmitted to the computer, and on its basis, phased fuel injection into the remaining cylinders is performed in accordance with the operating order of the engine cylinders. Typically, the phase sensor is installed at the rear of the cylinder head.
When the phase sensor fails, an out-of-phase injection of fuel into the cylinders occurs, that is, the engine enters the unphased fuel injection mode. The electronic control unit activates the Check Engine warning light on the dashboard. In this case, the engine starts to work unstable, up to a complete stop, a decrease in the dynamics of the car in different driving modes, the engine “troit”. In some cases, on the contrary, increased fuel consumption is noted. Replacing the sensor is straightforward. Usually you just need to use a wrench.
You can see partial information on how the phase sensor is checked in a separate topic.
Intake air temperature sensor
The sensor is abbreviated as DTVV or in the English abbreviation IAT. It is necessary so that the air-fuel mixture has an optimal composition for the operation of the engine. As a rule, the intake air temperature sensor is installed on the air filter housing or behind it, that is, in places where the air is directly drawn into the engine. In some cases, it may be part of a mass airflow sensor. Failure of the indicated element threatens unstable engine operation, floating idle speed (they will be either too high or too low), loss of dynamics, and power of the car. Also, with a faulty unit, there will be problems with starting the engine, as well as a significant excessive consumption of fuel, especially in severe frosts.
A sensor malfunction can be caused due to damage to its electrical contacts, failure of its signal wiring, low voltage in the electric vehicle network, a short circuit inside the sensor, and contact contamination. In fairness, it should be noted that this sensor, unlike many others, can be restored to its functionality, that is, not to replace. Sometimes elementary cleaning also helps (you need to do it carefully).
Checking the operation of the intake air temperature sensor is carried out using an electronic multimeter.
In most cases, the verification process is simple and does not take much time. Before performing the check, it is recommended to scan the memory of the electronic control unit for errors using a special scanner (for example, the popular ELM 327 device or its equivalent). This will simplify the verification of both a specific sensor and a malfunction of the car as a whole.
Sometimes situations arise when the location of a sensor is unknown. In this case, it is better to seek help from the manual. Also, on specialized sites there is information about the position of sensors on specific car models.
Before checking this or that sensor, you need to make sure that the signs of breakage indicate precisely the failure of a particular sensor. If you have doubts about this, it is best to seek help from a car service. Direct verification in most cases is carried out using an electronic multimeter capable of measuring electrical resistance and constant voltage in the range up to 12 volts. Therefore, purchase such a device if you do not already have it. It is not necessary to take expensive samples, an ample device from the middle price category (very cheap should not be bought either, since it may show incorrect data). Well, for the dismantling of sensors, you must have at hand the usual locksmith tools – wrenches, screwdrivers, and so on.