Questions and Answers

High Resistance Crank Angle Sensor Circuit
Q. Hi! I have a question regarding the symptoms and effects of high resistance in the crank angle sensor/wire/circuit? Could you please elaborate on how this signal affect the computer and what how the computer reacts. Thank you, James

A. I'm not an electronic engineer so I can't give you exact why's and wherefor's, but I think I can explain what a Crankshaft Position Sensor (CKP) is and what it does. Also, there is a difference between a Crankshaft Position Sensor and a Crank Angle Sensor (CAS).

In general, the CAS detects engine RPM and crank angle (piston position) and transmits these signals to the control unit. The sensor consists of a signal rotor plate and light emitting diodes (LED) located in the distributor. The signal rotor plate has 360 slits spaced at 1° on it's outer perimeter.

It also has six slits at 60°. intervals located inboard from the outer slits. The inner slits are used to detect the crank angle position (piston position). The outer slits are used to provide the 1° signal used to control ignition timing and engine RPM's.

The CAS uses a 5 volt reference signal and it creates a square wave signal, ON or OFF. If you looked at the signal with an oscilloscope it would look like this:

Now here is the way I see it, if there is a high resistance in the circuit, it would cause the 5 volt reference voltage to go down. If it gets too low, the computer will not see it and think the CAS is bad and throw a Diagnostic Trouble code.

I guess you can compare it to a light bulb. If you turn the switch on and off, you can see the light go on and off. If you stick resistors in the circuit, the light will still go on and off but the intensity will be reduced. If you keep putting resistors in the circuit, the light intensity will get so low as to be useless.

So I would have to say resistance in the CAS circuit will have little or no effect as long as the PCM can see the signal.