[doit659]

I own a 2011 328i Coupe with 128,000 miles that has been relatively trouble-free.

I brought it into a dealer to do a recall on the Vanos bolts, which they did for free but I decided to get some other stuff done out of laziness, such as a brake fluid change, coolant flush, and oil flush, since I was planning to do a brake pad and rotor job myself the next weekend (which I did without issue.)

I had an A/C issue (which I had fixed my self on my previous 2001 325i but didn't feel like doing it myself this time.) So, they added dye, and recharged it and it's also fine.

During their service, they fried the FRM (Footwell Module). After my independent research, I realize the FRM is a weak point with E90/92's but also realize it usually corrupts its EEPROM when the battery is disconnected BEFORE the modules "go to sleep". I suspect that is why it got corrupted.

In any event, although my car was outside of warranty, they replaced it free of charge, which was nice since it is a dealer $1300 charge.

HERE IS THE PROBLEM:
By chance, a couple weeks ago, I used my Foxwell scanner to test the car, as I routinely do.

I am now getting a persistent D904 K-CAN Line Fault on the CAS module (Car Access System) that will NOT clear.

Also, (related or not?), I get an intermittent D104 K-Can line fault on my RDC (Tire Pressure Monitor) that comes and goes randomly, which I CAN clear but pops up quite randomly.

As far as I can test, everything on the car functions properly with NO issues.

Now, I know the FRM module is physically close to the CAS module and that is the last place any electrical work was done on the car by the dealer. But (as far as I know) they didn't touch the CAS module.

I also know the K-CAN circuit on these cars is all running on the same circuit essentially for the 3 modules in question.

I want to figure this out because my understanding is that losing one K-CAN line will allow my car to still function, but if I lose BOTH K-CAN the car is DOA.

Also, I don't want to go back to the dealer and spend $300 an hour to trace stuff and then tell me I need to spend another $2000 to get entire wiring harnesses replaced, which is basically their approach.

I also know these cars are prone to corrosion on the harnesses and/or modules, although I have no obvious signs of water leakages.

QUESTION:

What would you recommend as a troubleshooting procedure?

1. Obviously, I will check the fuses but doubt this is the issue, since everything works.
2. I could disconnect the RDC (Tire pressure monitor) and see if the CAS D904 error clears.
3. I could open up the work they did under the steering column and see if there is something obvious with the wiring, like a connector that isn't seated or has a bad terminal.

Any thoughts? I appreciate any of you who read through this entire message that I wrote to be as thorough as possible.

Thanks,

Robert

[3PedalJake]

Sorry I don't have any specific tips, I'm new to figuring out canbus. I just had to splice a wire into it and watched this video first so as to have a better understanding of how it works. It's not specific to BMW, it's a generic tutorial but I found it helpful in understanding the basics of how the network works and the implications of various faults and troubleshooting procedures to isolate them.

[doit659]

THANK YOU VERY MUCH in helping me.