TRNW-2: 6t40 can bus diagnosing

[Justin Merritt]

Thanks for the replies. I did go to my dlc and tested across 6 and 14 for the dropping resistors. I had 120 ohms across 6 and 14. So I feel I’ve got a break somewhere. I know a few modules communicated and I know a few didn’t, the ecm and tcm was where I was concerned, so that is where I tried to start. In the morning I will get more info and post the vin, I will get a complete list on the modules that will communicate and the ones that will not. 

Justin 
Sent from my iPhone

> On Oct 19, 2025, at 5:38 PM, Fred Whitaker via trnw2 <trnw2 at trnw.net> wrote:
> 
> 
>  I think what I would do is get out my ohm meter, hook to pin 29 or 43 on ECM and just randomly check all the terminals on the TCM to see if any have continuity. If you do you proved the schematic is wrong. But if NONE of the wires have continuity I would be thinking about running jumper wires from TCM to ECM
> From: trnw2-bounces at trnw.net <trnw2-bounces at trnw.net> on behalf of Fred Whitaker via trnw2 <trnw2 at trnw.net>
> Sent: Sunday, October 19, 2025 5:07 PM
> To: Justin Merritt <justincmerritt5 at gmail.com>; Technical Discussion Forum <trnw2 at trnw.net>
> Subject: Re: TRNW-2: 6t40 can bus diagnosing
>  
>  Going by the way things "should be". The way I see it I agree a break in the 2 wires  according to the picture. But the odds of a break in just those 2 wires sure isn't very high.   I don't understand  the missing part about the wires going back to pins 6 and 8. I am also not understanding what Chris is saying about M8 and M9?
>  I would think the Bus on the Tehcm would use the same terminals no matter the rpo code,and something isn't adding up.
>  I also think you would have problems communicating with other modules if wires were open. Because the schematic clearly shows  terminal resistors in the engine control module.  Without the resistors there could be no communication in the other modules on the bus. If you go by that train of thought. The schematic is wrong,or we are misinterpreting it.
> 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 12:34 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
> 
> <image1.jpeg>
> 
> Sent from my iPhone
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