PCM won't read without TCM connected

[waynehartwig]

Like it says, I've got a E38 PCM from an 07 Silverado that is going into a buggy with a manual trans, so there is no TCM module. But when I plug into it, I can't see teh PCM unless I hook up a TCM as well.

Thoughts?

[STATESMAN]

Are you trying Write entire?

[Chris@HPTuners]

Like it says, I've got a E38 PCM from an 07 Silverado that is going into a buggy with a manual trans, so there is no TCM module. But when I plug into it, I can't see teh PCM unless I hook up a TCM as well.

Thoughts?

sounds like the wiring harness you have is for an auto. The TCM sits before the ECM on the bus so if you remove the TCM there is no connection to the ECM, you can jumper the pins i believe.

[waynehartwig]

Are you trying Write entire?

Can't even read it...

sounds like the wiring harness you have is for an auto. The TCM sits before the ECM on the bus so if you remove the TCM there is no connection to the ECM, you can jumper the pins i believe.

Yes. Any ideas which pins? Or what I need to jumper?

[Chris@HPTuners]

i *think* it's pin 10 to 14 and 11 to 13.

[waynehartwig]

Thanks! I'll give it a try tomorrow. But one question, though. I'm looking at the T42 connector on a bench flash harness I have and I can't distinguish the pin #'s. So if you are looking at the pins, with the big contact on the bottom, where is pin 1? Top left? and then read left to right - ie 1, 2, 3, 4 on teh top row? I don't have a TCM in front of me right now to see if it's labeled on there....

[Chris@HPTuners]

oh i figured you were talking about a T43 6 speed auto. I don't think T42 needs pins bridged it's not pass thru like the T43 is. Anyway the CAN bus pins are 6 & 7 on the T42.

[waynehartwig]

oh i figured you were talking about a T43 6 speed auto. I don't think T42 needs pins bridged it's not pass thru like the T43 is. Anyway the CAN bus pins are 6 & 7 on the T42.

Ok, so I just need 6 and 7 on the T42 then?

Which ones are they?

[STATESMAN]

On the T42 connector the can wires are 37 -38 just bridge the and it will allow communicate

[waynehartwig]

Found a diagram for the connector: it's pins 6-7 and 37-38 for the GMLAN.

Also, if you have the connector laying sideways, with the large lug on your right, pin #1 is the top left and then you read across. So 1-12 is the top row; 37-48 is the bottom row, with the large pin being 49.

[waynehartwig]

Still no workie. There is nothing on pin 7 in the connector, but I shorted 37 to 38 and that wasn't it.

Anything else to try?

[PitchblackC3]

Ever figure this out?

[waynehartwig]

Ever figure this out?

Yes, like Chris said in the second? post, the harness was preventing it from working. Basically put, the OBDII port hits the TCM and PCM and makes a loop. No TCM, no loop.

Hooked it up to a flash harness and no issues!