Tach quits trac off light comes on.

[twi119]

I have a 99 GP GT 3.80 82,000 miles. When driving the tach will quit and the trac off light will come on. It seems like the transmission may jerk a bit when this happens but the car keeps running OK. When you turn off the car and restart the problem disappears. It only happens inter-mintently. We have installed a new enigne brain box because it was putting out strange codes etc but this did not correct the problem. Have also run tests on ABS system seems OK. Any help would be appreciated. Thanks

[BNaylor]

Your symptoms is classic of a crankshaft position sensor (CKPS) going bad. Another thing you can do is remove the electrical connector at the CKPS and see if there is any corrosion on the contacts. The CKPS is located behind the crankshaft harmonic balancer on the passenger side of the engine. CKPS DTC error codes show up primarily as GM manufacturer specific emissions codes such as P13XX, etc. Good luck!






Thrasher CAI, DHP v1.0 PCM, SLP Headers,
3.25 SC pulley, CAIT GMAF, 2.5 DP/Hi-Flow CAT,
u-bend delete, 160 TS, ZZP Stage 1 72mm TB,
TB spacer, MSD 8.5mm wires, Autolite 103,
Goodyear Gatorback Serp. & SC Belt,
Nitto NT555R Drag Radials
1/4 ET: 13.210 sec. @ 104.490 mph
0 - 60 ft: 1.945 sec.

[BigBL87]

Originally Posted by bnaylor3400

Your symptoms is classic of a crankshaft position sensor (CKPS) going bad. Another thing you can do is remove the electrical connector at the CKPS and see if there is any corrosion on the contacts. The CKPS is located behind the crankshaft harmonic balancer on the passenger side of the engine. CKPS DTC error codes show up primarily as GM manufacturer specific emissions codes such as P13XX, etc. Good luck!

Thats probably what the problem is if its happened repeatedly. In my experience I had it happen once right after I'd had some engine work done, actually when I was on the way to have them run a diagnostic. It happened right as I was starting to park. I talked to the mechanic and he said to drive it for a while, and if it happened again to bring it in. It never happened again, and he said most likely it was the PCM just relearning the car and it happened to throw a wrong code. Just my .

[BNaylor]

Here's a link where we helped a gal with a GP that had a similar problem this past week:

http://www.automotiveforums.com/vbul...d.php?t=451777

When the PCM (brain box) was replaced was a crankcase variation learn (case learn) run? If not it may throw false misfire codes, store them in the PCM freeze frame data and possibly cause a fuel trim situation to the fuel injectors and driveability problems.

BTW - The PCM does not re-learn crankshaft position minimum and maximum and angle settings. They must be programmed in with a Tech II machine during a case learn. Otherwise, it's just using the old settings which may not be valid. If the case learn is required due to an absence of data the PCM will tell you by generating a P1336 DTC error code.





Thrasher CAI, DHP v1.0 PCM, SLP Headers,
3.25 SC pulley, CAIT GMAF, 2.5 DP/Hi-Flow CAT,
u-bend delete, 160 TS, ZZP Stage 1 72mm TB,
TB spacer, MSD 8.5mm wires, Autolite 103,
Goodyear Gatorback Serp. & SC Belt,
Nitto NT555R Drag Radials
1/4 ET: 13.210 sec. @ 104.490 mph
0 - 60 ft: 1.945 sec.