Before the use of computerized automotive sensors, fixing an automobile was as easy as, adjusting a screw on a carburetor.
Gasoline engines need the proper fuel and air mixture, with compression to squeeze the mixture all together. Only then can the spark plug ignite the mixture properly.
Today, Many car owners are not even aware of how many automotive sensors their vehicle actually has.
In the old days, It was a lot different. If you had fuel, spark and you were close to correct in your ignition timing, your car’s engine would run. As a result, Problems in these mechanical systems were relatively easy to solve.
The difference today is that a variety of engine parameters must be met and controlled.
Automotive Sensors Must All Be Working Properly
But, If one or more of the automotive sensors are not working. The engine may run poorly or not at all:
- Crank Position (CKP)
- Cam Position (CMP)
- Engine Coolant temp (ECT)
- Manifold Absolute Pressure (MAP)
- Mass Air Flow (MAF)
- Throttle Position (TPS)
- Accelerator Pedal Position (APPS)
- Heated Oxygen Sensor In Exhaust (H02S)
- Wheel Speed Sensor
- Tire Pressure Sensor (TPMS)
- Intake/Ambient Air Temp (IAT)
- Knock Sensor (KS)
- Oxygen Sensor (O2)
For example, What happens if a crankshaft position sensor (CKP) fails. Although mechanically sound, it has no way of figuring out when the spark plugs should fire. As a result, The engine will not start.
Similarly, With a failed (ECT) sensor, the computer might attempt to compensate for what it sees as a cold engine. Consequently, Adjusting the fuel injection and timing, causing the engine to run poorly.
You may even think that there is something wrong with the ignition system or the spark plugs. But, In reality there may be nothing wrong with the engine. Furthermore, It may be operating at its proper temperature. But, Because the sensor has told the computer that there is a problem, the computer sets out to correct it.
The computer can sense when something has gone wrong and can inform the driver with the “Check Engine” light.
Beyond Automotive Sensors, We Have Programs Called Monitors
They Look At The Values From These Proportional Integral Derivatives (PID)s To Make Sure Everything Is Working Right.
Some of these are:
- (EGR) monitor
- Evaporative emissions (EVAP) monitor
- Short term/Long Term fuel trims
- Engine warm up time (tests thermostat function)
- Misfire monitor (collected from (CKP))
So, Most Automotive Sensors Pretty Much Do The Same Thing:
One Way Position Sensors:
Pressure sensors, Temperature sensors, and (I will call them) “One way position sensors” like the (TPS). They all change electrical resistance that the (PCM) reads as a change in voltage. Because, The (PCM) sends a constant 5 volts and measures the return.
Rotational sensors like (CMP), (CKP), and wheel speed sensors normally use a pulse generating sensor. The difference is that they actually create an AC voltage signal.
They can also use a Hall-effect sensor that will create a digital DC voltage.
Oxygen Sensors (O2):
So, Oxygen sensors (O2) are in a class all their own. Because, They have a material inside them that creates a voltage (about 450 mV). As a result, Of having a difference in oxygen content on each side of the sensor. Therefore, The greater the difference, the higher the voltage (this pegs out just below 1 volt).
So, Always do your diagnostic homework first. Finally, Replacing a sensor won’t solve a drivability or emissions problem if the problem is not the sensor.
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