Weird problem

[jcurry05]

So I started my GP today and my TRAC OFF light was on and It wouldnt go off and as I started driving I noticed that my rmp meter wasat zero no matter what rmp I was at its was frickin weird. After I parked I restarted it and the trac light was off and the rpms worked. It woks fine now but I still want to know what it was all about and if it could be a signal for a bigger problem.
Does anybody know what this is about?

[BNaylor]

You have the classic symptoms of a failing crank position sensor (CKPS). When it gets real bad the engine will probably start randomly stalling out. The PCM module detects the loss and goes into fail safe mode and disables traction control. And it does give off any SES/CEL light in most cases.

We have a tech procedure for replacement of the CKPS at our Tips & Maintenance subforum.

[jcurry05]

Thanks BNaylor. I would buy one and replace it myself but I am at college right now and dont have the time or resources to do it myself here. I have seen them for around thirty dollars but how much do you think it would cost to get it installed. Is it very labor intensive/time consuming?

[BNaylor]

You're welcome. You have to be careful and get a few quotes. You can be subject to dealer or mechanic rip off. Actually it is no more than a 2.0 hour job but special tools are required like the harmonic balancer puller and special bolts. Around no more than $200 rings a bell including the part. Most of us DIY it but you have to have time available to do that and the right tools.

[troy1]

A case learn should be done also. That way you don't get misfire DTC's set

[jcurry05]

Case Learn?

[BNaylor]

For now I wouldn't worry about a crank variation learn aka case learn when replacing a crank position sensor. Although recommended it is optional. I've never done it. Problem is you will have to take it to a GM dealer where they most likely will charge you anywheres from $40 to $100. A GM Tech II scan tool is required.

Technically all a case learn does is reprogram the PCM module with high and low rpm thresholds to prevent false misfire DTCs. Or in other words, used to calculate reference period errors caused by slight tolerance variations in the crankshaft, the crankshaft balancer interrupter rings (harmonic balancer) , and the crankshaft position sensor Hall Effect switches. The calculated error allows the PCM to accurately compensate for reference period variations enhancing the ability of the PCM to detect misfire events over a wider range of engine speed and load. The CKPS is in a fixed, non-adjustable position on a SII 3800 engine so the chances of having any variance is very slim or nil, especially after replacement.

[jcurry05]

Oh ok. Does anybody know what the code is for the bad crank position sensor?

[BNaylor]

A bad crank sensor doesn't always give off a diagnostic trouble code (DTC) or set the SES/CEL light.

Codes vary. You have generic and GM extended. For generic for example DTC P0335 through P0339.

[jcurry05]

The SES light definently came on right after the rmps stoped working and the trac off light came on. So I assume I should expect a code of DTC P0335 through P0339?

[BNaylor]

Hopefully. Best to hookup the old scanner and see what it says. Keep us posted.