Desperate for help on Transmission and CAN-BUS communication

[menko]

Hi everyone,

2003 Eurovan VR6. While on my last trip, the transmission gear selector display started malfunctioning. It has been a while, but I believe it first didn't light up what gear it was in, but was quickly followed by all the gears light up together now.

When I start the car, I hear a loud click from under the shifter cover and that's when the display goes from just highlighting P to lighting all of them at the same time. The van shifts still, and hasn't gotten stuck in gear. My radio has a backup camera connected, and the camera will stay on all the time which should only happen when a signal is coming from the reverse switch.

I started with replacing the the gear range switch on the transmission, and cleaned those contacts. I reset the CEL and it immediately sets again from the transmission.

I have seen many older references to the Bobby Green solution the involves something related to pins that maybe are collapsing on some sensor being the culprit, but all the links to the procedure seem to be on dead forums. Trying to piece that together it sounds like it involves cleaning the pins on the sensor I've already replaced (https://www.thesamba.com/vw/forum/viewtopic.php?p=8827052)

Now you ask why I haven't used VCDS to troubleshoot further. That's where my bigger electrical problem comes into play. I can only communicate with the Engine controller (01). All other controllers are not responding. Several years ago I had to create a new K line that went from the OBD to the ECU directly.

I suspect based on this post (https://www.thesamba.com/vw/forum/viewtopic.php?t=735155) that perhaps I have some issues on the CAN BUS bridge. I just can't figure out what wires are actually the ones I need to look at.

Does someone have a picture of where this actually is? This was my best guess looking for 4 pairs of wires under the dash behind the fuses.

Any help on how to move forward here would be super appreciated. Electrical is not my strong suite but I can follow directions

Thanks in advance!

MJ

[Endopotential]

I'm following this with interest.

After my ECU fried last summer, I also had a similar but smaller glitch where my reverse lights and backup camera were always on. But the dash still displayed the correct gear, and the car drives fine.

https://www.thesamba.com/vw/forum/viewtopic.php?t=795730&highlight=

I replaced both the PNP switch (or I guess more accurately called the MultiFunction Transmission Range Switch MFTRS) down by the transmission, and also the 175 relay in the center console. Neither of this solved the problem.

Menko, you're also in the SF Bay Area as well? Valley Wagon Works in San Rafael is a very knowledgeable shop that finally fixed my ECU. He didn't spend much time troubleshooting my reverse light issue, but couldn't come up with a simple answer either.

[menko]

Thanks, yep I'm in Redwood City, so not too far away. I believe I checked the 175 relay when this first happened, I saw the youtube bypass video.

I will check my reverse lights, I'm sure they must be on. My guess is there's another transmission switch in the gear selector housing that is unhappy too.

I really need to find the CAN BUS junction so I can try and get VCDS to atleast get a connector to the transmission controller to give a little more info.

[trunnion]

The TCM communicates with a scan tool using K-line, not CAN. Check that your aftermarket radio is not shorting the K-line.
https://www.ross-tech.com/vag-com/aftermarket-radio.php

CAN bus junction is on the fuse panel relay position 5 (exactly what you have pictured).

[Endopotential]

Thanks for that useful bit of info Trunnion! You're definitely a great wealth of EV knowledge, and nice to know you're in the SF Bay Area.

Can you think of any reason why my rear backup lights stay on, and aftermarket Sony always has backup camera on after my ECU fried?
Van otherwise drives fine, and I've replaced that PNP switch down at the transmission as well as the 175 relay without any luck.

[trunnion]

[menko]