4L80E locked in second gear

mojo2013

New member
3
0
1
Location
Kansas City
I recently acquired an M1123 with a rebuilt GM transmission dated 9/10.

Truck originally shifted fine but is now struck in safe mode-second gear.

Fluid is in good shape, connections are together. Speedo is off by about 10mph (faster) than actual. Transfer case works well.



Any suggestions on where to start?

Thanks


Sent from my iPhone using Tapatalk
 
Last edited by a moderator:

papakb

Well-known member
1,671
227
63
Location
San Jose, Ca
Check the relay that provides +12v to the transmission control unit as a start. If you lose it the truck goes into limp mode. After that it's all the usual suspects.
 

AAVP7

Member
77
17
8
Location
Dortmund, Germany
Did you read out trouble codes from the transmission ?

As said above, there´s an amazing 4L80 troubleshooting manual out there, which is a very detailed reference and includes step-by-step instructions.

The tranny might default to safe mode if one of several sensors gives unplausible results. The manual will guide you how check them all.
 
Top
AdBlock Detected

We get it, advertisements are annoying!

Sure, ad-blocking software does a great job at blocking ads, but it also blocks useful features of our website like our supporting vendors. Their ads help keep Steel Soldiers going. Please consider disabling your ad blockers for the site. Thanks!

I've Disabled AdBlock
No Thanks