2009 GMC 1500 6.2L 4L60E to 4L80E Conversion

[[email protected]]

Has anyone ran into this problem?

Problem, Vehicle shows no codes but TCM will not command anything but 2nd Gear.

History, Customer has a 2009 GMC 1500 2WD with a Upgraded 6.2L. Customer shelled the 240k mile trans and decided to have a shop install a 4L80E. They got it installed and asked me to come by and help after a no crank no start symptom. Reviewed the schematics I found the original 4L60E transmission had an internal mode selector switch and the 4L80e of course has an external switch. I reviewed the 2009 GMC schematic and pulled the necessary pins from the Transmission Connecter and spliced them into an external harness wired IAW a 4L80E transmission and plugged that into a new external mode selector switch, the truck now starts and goes into gear. Also the instrument cluster position indicators work properly and all status data in HPtuners reflect properly. Used HPtuners to perform a segment swap from a 2009 Chevy Express Van which has a 4L80E and same TCM to the current TCM. Tested transmission and only gets 2nd gear, no codes. Continued reviewing the schematics and conversion adapter and identified the 4L60E for this 2009 year does not have an internal MPS, Manifold Pressure Switch assembly and wiring going to the TCM. I reviewd the 2009 Chevy Express 4L80E wiring schematic and it does utilize this switch and inputs. These are the only differences in the wiring between the two model vehicles I have identified.

My next TS step was to contact the MFG of the harness the customer bought, possibly they know of any known issues and could advise, the 4L60E to 4L80E adapter harness used is from ICT Billet. P/N WATRA31-18
I contacted ICT for tech support and they advised every time they had this problem it was caused by a improper segment swap. I brought up the missing MPS circuits and they said that most likely isnt the problem. I performed the segment swap again and still the same result, it will only command 2nd gear. Since I was getting the same result with HPtuners I decided to flash the TCM with my Snap-On PassThrough Pro with the Chevy Express 4L80e flash file and unfortunatly I get the same results. As far as I can tell, those three missing MPS circuits are the only difference between my current 4L80E installation and a factory Chevy Express Van.

If anyone knows if the MPS circuits are necessary or has any additonal information to add I would appreciate any feedback. Regardless, I have already ordered new pins to repin the TCM connector and run the missing circuits to the 4L80E. If this does fix the problem then I will provide an update just in case someone runs into this problem.

Thanks in advance.

[blindsquirrel]

Defaulting to 2nd gear is the typical result when you're missing power or ground at the trans 20-way connector. Real common for the wires to back out.

[Alvin]

I hate to just try to sell you something but we have a swap harness specifically for this that doesn't require any segment swaps and a version ready for the late 4l60-70's with internal mode switch.


Having only second gear doesn't sound related to not having a mode switch working. Stupid question.. It's got power on PIN E on transmission right?

[[email protected]]

Thank you for the replys and the input. Greatly appreciated. The 2nd gear only problem has been resolved and I would like to provide information as to what I found and corrected to get it working. I ended up following my gut and installed the three missing circuits from the Transmission Control Module which a stock 4L60E for year 2009 is not configured with. At the T42 connector these are Pin 24-Pressure Switch A. Pin 33-Pressure Switch C and Pin 44-Pressure Switch B. These circuits connect to N, P and R at the Transmission connector and are found on 4L80E's in 2009. As soon as I started the truck and placed it into D4 it commanded 1st gear. All other Drive range positions worked properly as well. The speedometer and final drive ratio's were configured as per the Chevy Express Vin I programmed it to so the speedometer and shift timing is way off but I call this a win for the moment until I can return and make some changes with HPTuners.

[blindsquirrel]

I think you accidentally restored a poor connection on the pink wire at the 20-way without realizing it when you went in there to add your other stuff.

[[email protected]]

It wasn't a poor connection I assure you. Those missing circuits are Inputs the TCM needs to monitor to determine the hydraulic functions of the transmission are working properly. The system was essentially in Limp mode.

[blindsquirrel]

I know you think that, I just still think you're mistaken. Possible causes of second gear start are missing voltage to the 1-2 solenoid, missing control to the 1-2 solenoid, or mechanical. And you didn't fix anything like a jammed center support piston or a cut o-ring.

[[email protected]]

What troubleshooting steps would you suggest I complete to verify/prove if I am mistaken?

[Fast4.7]

You need the MPS functioning or the 4L80E will default to limp home mode.