Those had a coil of wire wrapped around a magnet. It's that coil you would read the continuity of with your ohm meter meter.
With the newer three-wire sensors, that coil of wire can still be used, but you can't get to any test points to measure it. Most crankshaft position sensors and camshaft position sensors use "Hall Effect" transistors. Those turn on and off in the presence of a magnetic field. In this case, they have their own internal magnets, and a notch or a finger of a metal "pole piece" moving by disturbs its magnetic field. That change in the magnetic field is what turns the transistor on and off. That switching transistor turns circuitry in the sensor on and off. Because of that circuitry, there is no way to test one of these sensors with an ohm meter.
If you want to get really carried away, you can buy an expensive digital meter that measures frequency, but even most mechanics never do that. Your meter measures AC voltage, but it is only accurate when measuring a 60 Hz sine wave, meaning house current. Crankshaft position sensor signals are square waves, and never at 60 Hz. Your meter will likely not read the signal, even if the sensor is working.
You might get some indication on the DC scale, but I wouldn't even know for sure what to expect. Most position sensor signals switch instantly between 0.0 volts and 5.0 volts. During engine cranking, the voltage would change much faster than as often as the meter takes a new reading and displays it. At most all you'd see is random numbers bouncing around that wouldn't mean anything. If you were real lucky, you might see the change between 0.0 and 5.0 volts if you rotated the engine slowly by hand. Some sensors don't generate a signal until their magnetic fields are disturbed more quickly, as in cranking speed, so you still would not have any information of value.
The place to start is by reading and recording the diagnostic fault codes. Codes for position sensors don't always set right away, but if you do get a code related to the cam or crank sensor, understand those codes never ever say to replace a part or that one is bad. They only indicate the circuit or system that needs further diagnosis, or the unacceptable operating condition. First you have to rule out connector terminal and wiring problems, and mechanical problems associated with that code. In the case of a crankshaft position sensor code, there is probably a 75 percent chance a code is caused by the sensor, but you also must consider the air gap, (on engines where that is adjustable and critical), and whatever moving parts triggers those signals.
Mechanics use a scanner to view live data. That will list the sensors with an indication as to whether their signals are showing up at the Engine Computer. If they are, you're done there; move on. You didn't list any symptom, or reason for wanting to test a part, so we can't address that. The bottom line is you can't test a position sensor on your car. The Engine Computer does that for you.
Wednesday, December 7th, 2016 AT 6:26 PM