OK It's gettin' deep now!
Thread Starter
Staging Lane
Joined: Oct 2006
Posts: 70
Likes: 1
OK It's gettin' deep now! Been fighting a non-communication OBD II port issue for too long now.
Does anyone have the physical pinout for the TCM that that connects to an E38 ECU?
I have a diagram for the 2008 Silverado which should match mine but does not seem to. I have traced the CAN bus wires from the OBD II port to the TCM on what appears to be pins 47 and 48 and out to the ECU on pins 6 and 7. This is not what my diagram shows for these CAN bus lines.
The diagram shows them on pins 6 and 7 and 37 and 38? Also, I found battery power on what I think is pin 32 as expect but no power on pin 31 that should be IGN 1 pwr?
Any assistance would be appreciated!
Does anyone have the physical pinout for the TCM that that connects to an E38 ECU?
I have a diagram for the 2008 Silverado which should match mine but does not seem to. I have traced the CAN bus wires from the OBD II port to the TCM on what appears to be pins 47 and 48 and out to the ECU on pins 6 and 7. This is not what my diagram shows for these CAN bus lines.
The diagram shows them on pins 6 and 7 and 37 and 38? Also, I found battery power on what I think is pin 32 as expect but no power on pin 31 that should be IGN 1 pwr?
Any assistance would be appreciated!
Thread Starter
Staging Lane
Joined: Oct 2006
Posts: 70
Likes: 1
Well I finally found the problem quite on my own
so you can all stop searching for the answer.
It turns out that there are 2 power circuits to the TCM, one is B+ hot at all times which I found and the other is "IGN 1 volt" which I could not find but without a pinout diagram was just guessing anyway. Apparently this circuit is usually powered up by a relay in the fuse box called "Run Crank PCB Relay".
On my schematic this relay's output is called "AUX HVAC-IGN". Since I am not running HVAC I thought it would be a good choice to use to power my fuel pump since the fuel pump relay wire was missing from my factory loom?? I assumed that this "AUX HVAC-IGN" relay was there to cut off the AC during cranking but not so. The output (pink wire) is also supposed to go to power up "Trans IG1" (fuse 19) which apparantly provides a second 12v power source to the TCM for the CAN bus that passes thru to the ECU. The frustrating thing is I had continuity from the OBD II port thru the TCM all the way to the ECU but the CAN bus just would not talk to the ECU.
Long story short, I connected the pink output wire up to the switched ignition power on the "Run Crank" relay and viola, the OBD II scanner communicates perfectly!
My guess is the trans will start shifting properly now but I won't know until I can hot-lap it this weekend.
This was a self inflicted wound that took a ridiculous amount of time to troubleshoot that all comes down to vauge labeling on these schematics and non-existent pinout diagrams of certain connectors.
Time for a cold one!
so you can all stop searching for the answer.It turns out that there are 2 power circuits to the TCM, one is B+ hot at all times which I found and the other is "IGN 1 volt" which I could not find but without a pinout diagram was just guessing anyway. Apparently this circuit is usually powered up by a relay in the fuse box called "Run Crank PCB Relay".
On my schematic this relay's output is called "AUX HVAC-IGN". Since I am not running HVAC I thought it would be a good choice to use to power my fuel pump since the fuel pump relay wire was missing from my factory loom??
I assumed that this "AUX HVAC-IGN" relay was there to cut off the AC during cranking but not so. The output (pink wire) is also supposed to go to power up "Trans IG1" (fuse 19) which apparantly provides a second 12v power source to the TCM for the CAN bus that passes thru to the ECU. The frustrating thing is I had continuity from the OBD II port thru the TCM all the way to the ECU but the CAN bus just would not talk to the ECU.Long story short, I connected the pink output wire up to the switched ignition power on the "Run Crank" relay and viola, the OBD II scanner communicates perfectly!
My guess is the trans will start shifting properly now but I won't know until I can hot-lap it this weekend.This was a self inflicted wound that took a ridiculous amount of time to troubleshoot that all comes down to vauge labeling on these schematics and non-existent pinout diagrams of certain connectors.
Time for a cold one!
Last edited by markeheiden; Jul 9, 2010 at 12:31 AM.
