Transmission transfer case swap 4L60e

COME ON MAN

MEMBER
1999 GMC YUKON
5.7L
V8
4WD
AUTOMATIC
200,000 MILES

I have the SUV listed above with 4L60e. The transmission was shot when I bought it and I knew that. I also have a 1998 Yukon identical in every way. I took transmission from 1998 which worked perfectly and put it in the 1999, since doing so I have no first or fourth gear. Obdll scan doesn't even recognize the transmission is missing the 1-2 shift only kicks a code for bad 2-3 shift which I have to do manually. I understand first and fourth are electronically controlled so I assumed electrical problem. Checked all fuses, checked #13 pin on TCM for voltage, ohm reading on A and B solenoid, ran and erased codes, replaced TCM plug with original one from the bad 1999 transmission including all solenoid wiring. I know there were some ignition issues causing shift problems during the period for GM I'm not getting the codes that indicate bad ignition though. I am completely out of ideas and I can't lay under this thing any longer or watch another YouTube video. I need help. I am no mechanic or claim to be, I paid a so called mechanic to put transmission in and I've been left to deal with this. I know I should've taken it to a reputable shop but I chose to save some money and earned a huge pain in the butt. It has now became personal! Does anyone have any suggestions as to what I should do? I've read that transmissions and TCM are VIN specific they can't be swapped without flashing the computer? Any advise will be greatly appreciated.

3 Replies

ASEMASTER6371

MECHANIC
52,797 POSTS

Good morning,

I would take this to a shop and have them flash or program the module for the transmission. There were differences between the years and the module needs to know the transmission.

A shop with the proper scan tool or the dealer will be your options.

Roy

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Saturday, March 16th, 2019 AT 5:21 AM

COME ON MAN

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2 POSTS

I am unable to get to top transmission sticker, passenger side behind behind heat shield first 4 are 0TAP. I cannot remember the rest of the sequence off the top of my head. The transmission it replaced was 9LUD. The 3 digit number in the glove box that indicates drive drain specs is M30 on both Yukon's. Which should mean both trucks are transmission compatible. That is not the case for me somehow. I called Kerry Chevrolet in Alexandria KY and was told by the lead GM tech there that a flash could not be done to let ECM accept transmission or vise versa. I disagreed with his answer and chose to go in a similar direction. I took the ECM out of the 1998 which already has the transmission stored in memory and sent it off to be programmed to my VIN. So now I will have a ECM with performance program installed that accepts the transmission already and a ECM that runs my engine at factory settings and transmission with the exception of manually forcing grounds to shift solenoids to get first and fourth. It may not be the mechanical victory I was looking for, a wins a win. Hopefully I chose a legitimate ECU programmer. Time will tell.

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Tuesday, March 19th, 2019 AT 12:27 AM

ASEMASTER6371