Undiagnosed Limp Mode Issues. So I have been told?

Tiny
STAG1215
  • 2008 GMC SIERRA
  • 37,000 MILES

I have had my vehicle to 3 different dealers to diagnose the problem for a fix. No error codes are being stored is one issue and the service engine light is not on. Here is what happens, while drving at any speed, the truck seems to feel like it stalls. All indicator dash lights come on, (service engine, ABS, etc as well as park assist). After a brief second or so, all clears and truck resumes. I was told it is going into limp mode briefly but they cannot diagnose since there are no codes and the service engne light does not stay on. Acts like a huge hiccup. Lose everything. At high speeds, the truck will just roll through it and only the dash lights alert you it happened. Slower speeds can really be felt. I am afraid this could become a safety issue. Does anyone have any idea where to begin. I would think someone would know at the places I have been. Come back when the light stays on is what I am told. Maybe someone here can provide some input. Please

Do you
have the same problem?
Yes
No
Thursday, June 28th, 2012 AT 5:39 PM

5 Replies

Tiny
CARADIODOC
  • EXPERT
  • 26,033 POSTS

Check the positive battery cable where it bolts to the under-hood fuse box to be sure it's tight. I don't recommend removing it to clean it, (same with the battery cables), unless you use some type of "memory saver". GM has a lot of things designed in to lock up and need to be reprogrammed at the dealer when the battery is disconnected. Some of their vehicles don't do that but it's not worth risking an expensive repair bill over doing something so insignificant.

Also check the smaller negative battery wire where it bolts to the body.

Was this
answer
helpful?
Yes
No
Thursday, June 28th, 2012 AT 6:29 PM
Tiny
STAG1215
  • MEMBER

Thank You.I will check. I will advise if anything changes to keep you hopping. Supposedly, they had the truck apart and checked all connections but you never know.

Was this
answer
helpful?
Yes
No
Thursday, June 28th, 2012 AT 6:55 PM
Tiny
CARADIODOC
  • EXPERT
  • 26,033 POSTS

Another thing that might help for this is to connect a scanner with "record" capabilities, or a type of flight recorder that you control. When the problem occurs, you press the "record" button, then the mechanic can play it back slowly later to see what changed. Because that data passes through the scanner's memory, the recording actually starts a few seconds before you pressed the button.

That is fairly effective with intermittent running problems on older vehicles but for electrical problems it could also affect the power source the vehicle supplies to the scanner. Losing scanner power could erase anything it memorized or recorded. On newer vehicles from the last five to eight years, there are so much electronics and computer controls interconnected, that seemingly unrelated computers can cause the problem you described. Diagnosis of those things can be easier in some cases thanks to all the computers, but when no codes are being set, finding the cause can be real frustrating, as you're finding out.

Was this
answer
helpful?
Yes
No
Thursday, June 28th, 2012 AT 8:11 PM
Tiny
STAG1215
  • MEMBER

All cables seem to be very tight and secure. I gave them another twist and we had the same thing again this morning. I suppose that wasn't it. I will see what I can do about getting a scanner with record capabilites. This is going to be a real pain I think.

Thanks

Was this
answer
helpful?
Yes
No
Friday, June 29th, 2012 AT 11:22 AM
Tiny
CARADIODOC
  • EXPERT
  • 26,033 POSTS

Welcome to our world.

Was this
answer
helpful?
Yes
No
Friday, June 29th, 2012 AT 7:05 PM

Please login or register to post a reply.

Other Engine Computer PCM Limp Mode Questions