We test drove our 2011 GMC Sierra Dually Diesel Crew Cab with 117,224 miles on it and immediately got a check engine light. Upon inspection, it was determined that the catalytic converter was bad.

The dealer offered us one of these options:

1) our deposit back

2) a price reduction

3) a catalytic converter bypass kit.

We opted for #3. While pulling our 44' 5th wheel from Knoxville to Atlanta, after driving about 175 miles, the Reduced Power Warning Light came on and the power was reduced dramatically. I pulled into an AutoZone and turned off the truck. The AutoZone guy hooked up his computer and had me fire up the truck, but the problem was no longer apparent and there were no codes.

This has happened a number of times, but there are never any codes. One time the check engine light stayed on for about 50 miles but that went off and also left no residual codes. The problem occurs when I am accelerating hard while going uphill in order to maintain my speed. The truck is rated to tow 21,100 lbs and the fifth wheel, fully loaded, is just under 20,000 lbs. GMC seems to be at a loss as to why this is happening. Any ideas?

  • 1
    Go for option 1...
    – Solar Mike
    Commented Mar 20, 2018 at 7:34

1 Answer 1


I can not comment as I am too new to the site:

I would suggest getting an affordable OBD Adapter/Reader to have with you in the event that you're driving and the vehicle sets a code. Something like a BAFX Adapter and an Android/iOS App, or any basic stand-alone OBD Reader. They're worth the small investment to have, regardless of this situation.

Here's the monkey in the gear; I feel like it's a transmission issue, and those generic readers will generally not read Transmission Codes.

Limp-Mode can be triggered by any number of issues.

  • I'd do a full inspection of all wiring. I'd start troubleshooting like this:
  • Remove, clean, and re-tighten all battery terminals and grounds.
  • Re-seat all visible connectors.
  • Look for puddling/Staining/efflorescence at/around connectors and electrical components.
  • Check the condition of the Transmission Fluid.
  • Full basic maintenance checks are obligatory. Check All Fluids.

I hope this helps.

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