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Crank Position Sensor and Ignition Control Module


sisson_d
04-04-2017, 02:35 PM
I have a crank but no spark condition that looks like it will likely be the Ignition Control Module (ICM) on my '08 Pontiac Grand Prix. The ICM is not cheap and I want to rule out anything else before spending the money.

I have found that the ICM is receiving a strong 12volts and has a good ground. The diagnostic procedures require next checking the output and input for the Crank Position Sensor. But I don't have the tools necessary and, with no car, I can't get to the store.

But I do have a scan tool. And it shows the fluctuating engine RPM (about 165-200RPM) when I'm cranking the engine. I believe, from what I've read, the CPS gets it's power and sends back data through the ICM. So, if that's true, and I have RPM data on the scan tool, is it safe to assume those measurements I'm supposed to read to/from the ICM are fine?

Thanks in advance,
Doug

maxwedge
04-04-2017, 06:08 PM
Looks like the cps is working​.

StumpedGMowner1
04-04-2017, 08:45 PM
Cam shaft sensor controls spark. Crank sensor controls rpm data and fuel injection. Seen a failed or failing cam sensor not set any engine trouble codes too.

sisson_d
04-04-2017, 09:17 PM
Cam shaft sensor controls spark. Crank sensor controls rpm data and fuel injection. Seen a failed or failing cam sensor not set any engine trouble codes too.

Good to know. Thank you. I incorrectly assumed the camshaft sensor would set a code and thought it was involved directly with the CPS for RPM and other stuff.

Now that kind of worries me. Lately, every time I can't say a part is to blame with 100% certainty, the part I buy ends up not being the bad part. I felt about 80% confident and need this daily driver working again ASAP, so I ordered the ICM earlier. I was able to get a new AC-Delco unit from rockauto (next business day shipping included) $20 cheaper than aftermarket at the local parts stores. I won't get that until Thursday most likely.

Tomorrow I'll grab a camshaft sensor locally, since it's fairly cheap, and try that out.

If I only bought 1 part, it would have ended up being the other part. Now I'll have both. And rockauto's never given me a problem with returns if it's not the ICM. I'd just have to pay the return shipping.

Thanks again for the heads up.

-Doug

sisson_d
04-07-2017, 09:50 AM
Okay, I installed the new ICM yesterday (standing outside in the freezing mist with 102 fever) and the car started right up.
I also did the cam sensor the day before, and that did nothing. But it gave me a chance to confirm the wiring for the sensor was okay. And the part it replaced had 108k miles on it. So, for $36 I wouldn't consider it a waste of time.
Thanks to all that helped!

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