RPM Question

My RPM gage on my Pontiac Grand PRrix 98 se series 2 has been going fine and then suddenly just drops to 0. I then have to turn the car off and back on for it to work. This only happens maybe once a week and there has been no codes set. Anyone experience this problem or have any solutions?

Does it flutter before it drops? How hard do you usually drive?

No it does not flutter or anything of that nature. I will be driving along normally and then the rpm gage will just simly cut out and drop to zero. I don't drive hard at all, I would say just normal or casual. Most of my driving is highway miles and 1/3 city.

Well I'm not sure then... I don't know if the grand prix makes use of a basic gear driven tachometer. If it does, you may be able to check the gear in the dash... but I wouldn't recommend pulling your dash out unless you're sure if there's a problem back there, or it's just a waste of time.

The tach is electronic. The tach signal originates at the ignition control module (ICM) and then to the PCM module. From there to the rpm gauge at the IP Cluster.

Have you had the gauge cluster out for any reason? If so, check your connections, if not, I would look into getting a replacement from a salvage yard, or I have seen them for sale on eBay.

No I have never had the cluster gage out for any reason. It just simply goes out sometimes. The low traction comes on too when it does go out though. Thanks though for at least trying

when the guage drops off, does the car run any different? If it does maybe suspect a bad crank position sensor. If the car runs the same as it always would, its got to be instrumentation problem.

Well it dosen't drive differently at all. So it must be in the cluster then.

I wouldn't count on it and that may be an invalid assumption especially with the accompamying TRAC light. A bad cluster does not cause that. Most likely the PCM module has detected an abnomally related to the 18X and 3X pulses at the ICM module which originate from the crank position sensor (CKPS). The CKPS is two sensors in one.

but if one of the two sensors in the crank sensor drops out, the pcm would pick up on that and trip the SES, wouldnt it? And the track off light would be lit for the brief second.

The PCM does pickup on it and goes to internal calculations of last known position (fail safe mode), however, in many cases no DTC will set hence no SES/CEL Mil light.

One classic symptom of a flaky CKPS is getting the trac light and seeing the tach drop off. There may or may not be a stall. As it gets worse it may stall.

Before replacing the CKPS I would control substitute the ICM module with a known good one, double check the CKPS electrical connector and the electrical connector to include wiring harness at the side of the ICM module. If all the foregoing check outs then replace the CKPS.

This is an old issue discussed for many years on this forum and 99% of the time the CKPS resolves the issue. :grinyes: