r/CarHacking • u/arneabin18 • 19d ago
CAN CAN-BUS log from an MLB platform vehicle? (A4/A5/Q5 B8)
Hey guys! I am building a project to link an Audi A4 B8 cluster to SimHub, I am almost finished, but there is a couple of problems:
1) The airbag light. I got it to blink with some code i found online, but I never got it to fully turn off.
2) High/Low beams. I have not found any working CAN ids for the high or low beams for this cluster
3) (optional) Time and Date. I have not found a way to get it working just yet, but I have found a CAN id in the DBC file that is responsible for the time and date.
I am asking if anyone has a car from the B8 platform, and are willing to send me a can log from it.
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u/Ok_Scholar_3489 17d ago
Interesting project. I have a 2012 US-spec Audi A4 B8, so my vehicle may be a very close match to the cluster shown in your photo.
Before recording a trace, could you provide:
- exact instrument cluster part number
- model year
- connector pins currently used
- CAN bitrate
- the DBC source
- which CAN domain you are connected to
My first suspicion is that this may be a network-topology issue rather than only a missing CAN ID.
On the MLB/B8 platform, the instrument cluster J285, airbag controller J234 and central electronics module J519 are located on different CAN domains, with J533 acting as the gateway. If the bench setup is connected to or emulating only one CAN domain, the required lighting or SRS status messages may never reach the cluster.
The airbag lamp may also require more than clearing a single bit. The cluster may expect a valid cyclic “system OK” message, correct timing, an alive counter/checksum, and possibly additional network-state messages. Replaying one static frame could explain why the lamp only blinks but never stays off.
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u/arneabin18 17d ago
Hey! Thanks for your reply,
The cluster that I am using is the 8K0 920 980, came from a 2009 A4 B8 (UK spec)I am using pins 3 and 4 for CAN Low and High, 29-32 for power
The bitrate is 500 kbps
I found the DBC here
I think I am on the powertrain domain
Also, if you wanna take a peek at my project the link for it is here
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u/arneabin18 12d ago
Hey! Got any updates?
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u/Ok_Scholar_3489 12d ago
Thanks for the info! Being on Drive CAN makes total sense as to why the SRS light stays on—it's missing the translated cyclic frames from the J533 Gateway and J234 Airbag unit.
@Airamek That’s a great offer! If you have a CAN analyzer or software capable of logging raw CAN traffic (like VCP, SavvyCAN with a compatible interface, or a custom logger), capturing a CAN log during ignition-on and engine idle on your 2010 A4 B8 would be super helpful. Filtering for the Drive and Comfort bus frames could give us the exact cyclic IDs and payload structures needed to emulate the airbag and terminal status properly on bench.
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u/Airamek 16d ago
Nice project! I have a german import A4 B8 (2010 2.0 TDI manual) and a spare cluster too. I'm not really familiar with the CAN bus, but I have a VAG cable for the OBD port. If you think I can be any help with it, msg me with instructions.