Crank sensor testing? - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 07-29-2007, 10:51 PM   #1
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Default Crank sensor testing?

Since a crank sensor is pretty much a crank sensor no matter the year, I thought I'd post this in the general chat...

Is there an "approved" way of testing crank sensors? After reading through my Haynes manual'* wire diagrams, I put power from a 9v battery to the 10v in and sensor ground terminals of the sensor, and put a multimeter on the two output terminals. Then I had my wife crank it a few times. While cranking and while at rest, I never saw any voltage. If it was working, I should see it flicker some voltage, or possibly come to rest with voltage on, right? Or would it be so brief that it wouldn't necessarily register?

Or would I need to have the multimeter hooked to one of the output terminals at a time, and vehicle ground? That doesn't seem right, but I just wanted to throw that out there as a possibility...

I suppose that if nobody knows, I could also run the same test on my LeSabre, but I'm a bit uneasy about possibly hurting my only remaining running car at the moment. So hopefully someone has done this before, or knows what the result of the test should have been for a good one.

For some background, my '89 is parked dead in the driveway from lack of spark. I've eliminated plugs, wires, coils, ICM, fuses... pretty much everything but the crank sensor and ECM. I'd just try swapping in a new one, but I really don't want to start throwing parts at this car, since I hope to get it running and sell it. Not to worry though, I plan on replacing her with another Bonneville.

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Old 07-30-2007, 02:17 AM   #2
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Actually, looking again at those diagrams, I might have done that wrong. I'm still not sure, but I might have needed to measure between one of the output terminals and the sensor ground, not between the two sensor terminals. The Haynes manual has no procedure for testing this, only a diagram which tells me visually that it should be possible...

But again, if anyone else has a FSM or personal experience with these little buggers, that would be awesome and appreciated.
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Old 07-30-2007, 06:22 AM   #3
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Things (pulses) happen to fast for a conventional multimeter to see. I would think an Oscilliscope would be what is needed to check operation of a CKP.
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Old 07-30-2007, 02:36 PM   #4
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Well, I didn't figure I'd see individual pulses, but I hoped to at least see a slight "average voltage" increase. No?
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Old 07-30-2007, 03:38 PM   #5
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I don't believe the crank sensor can be checked without an oscilloscope.

If you have 12 volts at the pink/black wire going to the ICM (with key on) & a good ICM then the problem is either the crank sensor or wiring between the sensor & ICM.
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Old 07-31-2007, 01:58 AM   #6
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Thanks for the replies. You may well be correct that it can't be tested without a scope. I might still try my revised method, just for *&G. If it did work, it could save a lot of people some time and cost by not having to replace a crank sensor without knowing if that is the problem.

That said, I think it IS my problem. I do have power to the pink/black in the harness, and I already tested the harness from the ICM to the crank sensor. I''ve poked and probed just about every wire I can think to test in that car, and it'* pretty much down to the crank sensor or the ECM. The ECM doesn't display any other odd behavior though, so I have to lean toward the crank sensor.
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Old 07-31-2007, 02:07 PM   #7
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NOT a general chat topic? Sorry, I thought it was non-specific enough. My bad.
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Old 08-01-2007, 01:55 PM   #8
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Results of the second test:

I tried my revised test for the crank sensor (go right for 12v off the battery and vehicle ground for power to the sensor, while measuring the two outputs individually against the same ground). Using this method, I get no voltage at a stop, but some slight voltage as it cranks, from each of the outputs.

So I suppose that it could still be bad... not enough of a signal, or maybe not working at all under the usual 10v input. I was really hoping for a more conclusive "This is DEAD" result though.

I guess for any conclusive results, at least for a sensor that might be marginal, a scope is probably needed. This test might still be conclusive if a sensor is all the way dead though.
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Old 08-04-2007, 05:05 PM   #9
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Just to update the topic for posterity:

I did just get the car running, and the problem was NOT the crank sensor. So, the activity that my ghetto-crank-sensor-test showed on the meter was what you'd see from a good sensor.

Hope this helps someone else down the road...
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Old 09-27-2007, 02:57 AM   #10
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Default Car running?

You got it running?
What was the problem?
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