Today’s modern automobiles have a variety of sensors. These sensors built into their engine to ensure that the owner can identify and prevent possible issues. Before they result in breakdowns can result in expensive repairs. These automobile engine sensors also ensure that the vehicle is operating at its most efficient. Many owners are not even aware of the amount of sensors built into their automobiles engine and what value they add.
As car owners, knowing the function of these sensors is very important. In order for you to understand the definition and the function easier, here is a list of popular car engine sensors:
The Mass Air Flow Sensor (MAF)
From different types of sensors used in cars, The Mass Air Flow Sensor (MAF) is a computer-controlled sensor. Mounted ahead of the throttle body on multiport fuel injected engines. The MAF sensor monitors the volume of air entering the engine. The sensor uses either a hot wire or heated filament to measure both airflow and air density.
The sensing element in MAF sensors can be easily contaminated causing hard starting, rough idle, hesitation and stalling problems. Cleaning a dirty MAF sensor with electronics cleaner can often restore normal sensor operation. And save the cost of having to replace the sensor (which is very expensive!).
Vehicle Speed Sensor (VSS)
Vehicle Speed Sensor monitors vehicle speed so the computer can regulate torque converter clutch lockup, shifting, etc. The sensor may be located on the transmission, differential, transaxle or speedometer head.
A problem with the vehicle speed sensor can disable the cruise-control system as well as affect transmission shifting and converter engagement.
Used on both carbureted and fuel injected engines since 1981, the oxygen (O2) sensor is the key sensor in the fuel mixture feedback control loop.
Mounted in the exhaust manifold, the O2 sensor monitors the amount of unburned oxygen in the exhaust. On many V6 and V8 engines, there are two such sensors (one for each bank of cylinders).
The O2 sensor generates a voltage signal that is proportional to the amount of unburned oxygen in the exhaust. When the fuel mixture is rich, most of the oxygen is consumed during combustion. So there is little unburned oxygen in the exhaust. The difference in oxygen levels between the exhaust inside the manifold and the air outside creates an electrical potential across the sensors platinum and zirconium tip. This causes the sensor to generate a voltage signal. The sensor’s output is high (up to 0.9v) when the fuel mixture is rich (low oxygen), and low (down to 0.1v) when the mixture is lean (high oxygen).
Sensor output is monitored by the computer and is used to rebalance the fuel mixture for lowest emissions. When the sensor reads “lean” the PCM increases the on-time of the injectors to make the fuel mixture go rich. Conversely, when the sensor reads “rich” the PCM shortens the on-time of the injectors to make the fuel mixture go lean. This causes a rapid back-and-forth switching from rich to lean and back again as the engine is running. These even waves result in an “average” mixture that is almost perfectly balanced for clean combustion. The switching rate is slowest in older feedback carburetors, faster is throttle body injection systems and fastest in multiport sequential fuel injection.
Manifold Absolute Pressure Sensor
The MAP sensor is mounted on or connected to the intake manifold to monitor intake vacuum. It changes voltage or frequency as manifold pressure changes. The computer uses this information to measure engine load so ignition timing can be advanced and retarded as needed. It performs essentially the same job as the vacuum advance diaphragm on an old fashioned mechanical distributor.
Some MAP sensor problems are not the fault of the sensor itself. If the vacuum hose that connects the MAP sensor to the intake manifold is loose, leaking or plugged, the sensor cannot produce an accurate signal. Also, if there is a problem within the engine itself that causes intake vacuum to be lower than normal. Such as a vacuum leak, EGR valve that is stuck open or leaky PCV hose, the MAP sensor’s readings may be lower than normal.
A spark knock sensor ensures that the fuel is burning smoothly and not detonating (exploding erratically). Detonation can cause the head gasket to fail, piston lands to crack and rings to break, as well as possible rod bearing damage. Some engines have two knock sensors.
Fuel Temperature Sensor
The Fuel Temperature Sensor is another sensor that ensures your cars fuel consumption is at its most efficient. The colder the fuel is the more dense and the slower it burns while when the fuel is warm is burns faster. There are many car parts that can get damaged when the car runs out of fuel. So this sensor ensures that the right amount of fuel is injected to keep the vehicle running smoothly while being as efficient as possible.
Another important part in car sensors list is the Voltage Sensor. This sensor manages the idling speed of the car and ensures the speed is increased or decreased as necessary.
Usually located on the cylinder head or intake manifold, the coolant sensor is used to monitor the temperature of the engine coolant. Its resistance changes in proportion to coolant temperature. Input from the coolant sensor tells the computer when the engine is warm. So the PCM can go into closed loop feedback fuel control and handle other emission functions (EGR, canister purge, etc.) that may be temperature dependent.
The coolant sensor is a pretty reliable sensor, but if it fails it can prevent the engine control system from going into closed loop. This will result in a rich fuel mixture, excessive fuel consumption and elevated carbon monoxide (CO) emissions. Which may cause the vehicle to fail an emissions test.
Throttle Position Sensor
Mounted on the throttle shaft of the carburetor or throttle body, the throttle position Sensor (TPS) changes resistance as the throttle opens and closes. The computer uses this information to monitor engine load, acceleration, deceleration. And when the engine is at idle or wide open throttle. The sensor’s signal is used by the PCM to enrich the fuel mixture during acceleration, and to retard and advance ignition timing.
If you have not done your diagnostic homework and are replacing a sensor because you think it might be bad, you may be wasting money. Replacing a sensor won’t solve a drivability or emissions problem if the problem is not the sensor. Common conditions such as fouled spark plugs, bad plug wires, a weak ignition coil, a leaky EGR valve, vacuum leaks, or low compression. Also dirty injectors, low fuel pressure or even low charging voltage can all cause drivability symptoms that may be blamed on a bad sensor. If there are no sensor-specific fault codes, these kinds of possibilities should be ruled out before much time is spent on electronic diagnosis.
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