Ramjet

Hello guys .I have a 2007 tahoe 4x4 and I am having some problems with communication to the TCM being lost . if the truck is off with the key on I can scan the TCM and I get codes P-2544 and U0101 . but when you start the engine the data is lost to the TCM , the gear shift select indicator will jump around between gears and the door locks jumping up and down and then the indicator will go out completely when com is lost . I can communicate with the ECM and the BCM when running but not the TCM so only the TCM communication is lost when running. I have checked all the grounds including the G-110
I have also check for backed out pins . and checked wires for rub through by the park brake lever . I have checked for voltage drop in all the main battery cable but all are good ,even replaced some ends and soldered them on that tested well but did not look good . I checked the resistance at the ALDL and it is 60.9 ohms (I think between 6 and 14 pins).

I guess what I need now is a pin out for the TCM so I can check the power and ground circuits at the TCM to see if one of the circuit is failing when the demand on the circuit changes when running . does anyone have a pin out of the TCM for a 2007 tahoe .

just a hunch but does the TCM ground or main power T into any other circuits . if so locations of these junctions would be a great help .


thanks guys for any help .cheers Roger

01WS6/tamu

iTrader: (36)

Follow the diagnostic chart for the related code you need a scanner and the ability to flash the new TCM it comes unprogrammed.

Ramjet

thanks for the reply


just got the pin-outs today and checked all the power and ground circuits
to the TCM .

pin 32 batt good
pin 31 ignition good
pin 49 ground good

pin 37 GMLAM - good
pin 38 GMLAM + good

pin 6 GMLAM - no ground
pin 7 GMLAM + only get signal when using external ground

I do have a scanner and that's how I recovered the codes but it's not much good for testing GMLAM circuits . I tested them with my digital oscilloscope set to Hertz . testing between pin 37&38 I get a good reading ,but I can only get a reading from GMLAM pin 6 when using the chassis for a ground .

what I need now is a wiring diagram to show where pin 6 goes . I believe the GMLAM circuit going to pin 6 must have a high resistance connection somewhere .

cheers Roger

Ramjet

well it seems my module has failed , pin 6& 7 send the GMLAN signal to the ECM terminating resistor. funny as a little test, as the module only seem to fail after getting warm . I put the module in the freezer for a while and the truck will run like a champ for 15 min and then crap out again . after it craps out you can leave it for a hour and it will still not run correctly but put the module back in the freezer and she runs like a champ again for 15 min . so for sure the module is failing . my only concern is if something in the driver circuit is shorting and overheating the module.seems unlikely as the truck runs fine until the module acts up .