TRNW-2: 6t40 can bus diagnosing

[Dan Hogan]

Justin,

The MF3/MZ0 are the RPO codes for the manual transmission equipped vehicles and it's trying show the HS CAN bus doens't connect to the TECHM module since it's not present for this RPO code.

MH8/MH9 indicates the 6T40 trans and since yours is auto equipped 6T40 assumed, this is the wiring path you should use.  Ignore the MF3/MZ0 as its not present.

This is how GM does schematics and RPOs in their diagrams.

As shown, the High Speed CAN bus travels through the TCM (TECHM) and the ECM is the last module in the bus and includes termination for the end of the bus (60 ohms - 60 ohms = 120 ohms).   If you are measuring no continuity in the bus wires connecting between the two modules, I think you found your issue.  This would leave the bus unterminated and the TCM communication would also be affected.

If you post the VIN for the vehicle, I'll be glad to look over the full schematic to help you diagnose.


---


Dan Hogan

Buster's Transmission Service

https://busterstransmission.com

704.847.5321

________________________________
From: trnw2-bounces at trnw.net <trnw2-bounces at trnw.net> on behalf of Justin Merritt via trnw2 <trnw2 at trnw.net>
Sent: Sunday, October 19, 2025 1:34 PM
To: trnw2 at trnw.net <trnw2 at trnw.net>
Subject: TRNW-2: 6t40 can bus diagnosing

Hello all,
I am working on a 14 Chevy Cruze 1.8 engine. I am chasing a loss of communication of both the transmission and engine control module. I struggle when it comes to testing wiring on the can bus lines, I just don’t have enough experience with it. I’m determine to figure this one of for a learning experience. I have included a diagram of some wiring I am testing, and I have continuity between pin 29 and 6 and 43 and 14, but I do not have continuity between 29 and 7 and 43 and 8. The diagram cuts off, but the mf3/mz0 squares just loop around the tcm and back into the wires 6 and 8 of the tcm.  Would I be thinking right that I have a break in the 2 bus wires 29 and 7, and 43 and 8 that is causing my no communication?
Thanks for any help.
Justin

[cid:2bcc003d-9b28-430c-a726-8969535e3274 at namprd17.prod.outlook.com]

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