93 gmc Rebuilt 4l60e stuck in "limp mode"

**SledFreak** · 05-28-2012, 10:06 PM

I have a 93 GMC k1500 (4x4 w/ 350). Long story short i picked up a rebuilt '94 4l60e from a friend that he had bought for a different project a few years ago and never got around to it. Lost the pump in my old trans and everything worked fine before.

With the rebuilt 4l60e and new torque converter in, its stuck in limp mode (third gear when in drive/ odrive, reverse works, and 1 and 2 both are 2nd )
I've checked my wiring and the plug on the trans and transfer case and everything appears to be good. Unplug the main plug from the trans and no difference. Check the main plug for voltage and it has ~12 V in some of the wires. No check engine lights are on and motor runs good. Speedometer works.

What i'm stuck on is where to start trouble shooting. Its either an electrical problem with my truck, electrical in trans, or hydraulic problem in trans. I'm ruling more towards and electrical problem with the trans itself but don't want to leave anything else out. So how do i go about troubleshooting the transmission with out pulling it out? Is there resistance checks that can be done from the main plug?

**JBecker** · 05-29-2012, 05:52 AM

Did a reputable shop do the rebuild? I would say it is in the trans if your truck drove fine beforehand.

**JBecker** · 05-29-2012, 05:55 AM

I sold a 4l60e to a guy a while back that was sitting for years, once he put it in he realized the pump was bad from sitting because it

**96Z71Siverado** · 05-29-2012, 07:00 AM

Its lost communication with the PCM somewhere or there is a software missmatch

**SledFreak** · 05-29-2012, 09:17 PM

Pretty sure it hasn't lost connection with the pcm. If the pcm is putting the trans in limp mode, would there be a check engine light on? Not sure how there could be a software mismatch.

**SledFreak** · 05-30-2012, 10:16 PM

Update: Check for any codes and there are no codes stored on OBD. I've pretty much decided to pull it out and tear it down my self.

**96Z71Siverado** · 05-31-2012, 08:53 AM

Originally Posted by SledFreak

Pretty sure it hasn't lost connection with the pcm. If the pcm is putting the trans in limp mode, would there be a check engine light on? Not sure how there could be a software mismatch.

Then there is a mechanical issue within the trans causing the problem..I deal with far newer vehicles on a daily manner , and when the CAN network goes down or a we have a pin push out the trans goes into 3rd gear default, but then again Im dealling with 2014 MY and above..so its a far cry from the 90's versions