mcollinstn

Okay, daughter has 2013 C250 Sport.
Great car. Bought used out of Texas.
Has had zero problems since we've had it (bout 8 months).

Started hearing whining about low tire messages, which made sense cause we just hit our first cold snap. Wife ran an errand in the car, and noticed the COMAND screen would occasionally "turn off" while driving. She asked daughter who said it had been doing that for a while.
Then they hollered at me.

So I shrugged it off and said I'd bring it to my shop and check it out - probably needs a reset..

So this morning, I drove it in to work. Tires showed 26 psi. No surprises there, also no reason for hysteria. About halfway to work, I had not seen the display go dark, so I called and asked exactly what makes it go on and off. I heard all sorts of guesses, but nothing tangible.
So, at the next stoplight I noticed the COMAND display was dark. Totally dark, black. The radio was playing, I could change stations, etc. Display remained black. I let off the brake and accelerated from the stop, and the display came back on. I wondered if there was a connection that accelerating "helped", but I was in morning traffic. I got off the main road and pulled into a secondary street that I knew had bumpy places. I was going to try to shake it real good to see if it did anything. I applied the brakes and the display went out. I let off the brakes and the display came back on. Brakes off, display on - brakes on, display off. Repeatable. I stopped the car, (display turned off while braking) and put the car in neutral and let off the brakes. Display came on when I let off the brakes. So I went ahead and drove thru bumpy pavement - display stayed on. I stopped the car (display turned off), put it in reverse - rear camera popped up on the display just like it is supposed to. Brakes on, brakes off, while in reverse the backup camera remained lit up on the display properly. I put the car in D and started moving, display went to the radio screen. Brakes, display turns off, No brakes, display is on. Same thing in NAV screen. Seems clear that the COMAND video output is going black (as opposed to the display unit itself bugging out).

When I got to my shop, I pulled the COMAND fuse and went on in to work. After a while I put the fuse back in, hooked my SOLUS scantool up, read all the system codes (no engine or trans codes, a low voltage ABS code, a handfull of central control module codes, etc, no COMAND related codes). I logged the codes and cleared them all - twice.

The low voltage codes I saw did not have a "date code" with them (my Audi software will allow me to see WHEN the code was initially flagged), so I have no idea when those codes were stored. I shrugged it off and figured they might be old codes from sometime in the distant past (body control module codes don't vanish on their own - you have to clear them or let the memory die). So I cleared them all.

No change - the fuse reset didn't help. The code clearing didn't affect the weird brake pedal triggered display issue.

I'm dropping this on here to see if ANYBODY has any clue what could be tying the brake light or brake pedal or brake pressure or ABS pressure sensor TO the COMAND video output.......

Clues?
Ideas?

Mike C

Vcool

Hi, I am driving a w204 C250. And I am having the exact same problem. When I apply brake, reverse camera screen appeared. When I release brake, it went normal. Did you manage to solve it? I was thinking if it has anything to do with ECU? As recently my ECU is having issue and just got it repaired.

mcollinstn

Crap no.
A year later, same issue. It definitely looks like the screen "swaps to" a different video input when brakes are applied, then swaps back to "comand" when brake is released. Backup cam only shows in reverse, so I'm not sure if the screen is swapping to the backup cam with the brakes, but the cam is "off" or if it is a 3rd input.. But the car works 100% perfectly aside from that, and the comand knob continues to functioneven when the screen blacks out (changing radio stations, etc).

Its very weird. I don't like it. I wish it was fixed.

Daughter has basically accepted it as normal behavior.

mcollinstn

okay, first off I found out that this cat has the AUDIO 20 info system, and not the COMAND. The AUDIO 20 system has no built in capability or input or menu structure to support a backup cam. The backup cam in the car was installed "after the fact".
Nothing in the info system was changed. A video switcher was inserted between the info system and the dash display.
there is a trigger wire that is used to swap the video signal to the display from A (info system) to B (camera feed).
This trigger wire is supposed to be to a REVERSE SIGNAL
There are several spurces for a reverse signal, but on this car a wire was run all the way to the taillight and tied into the backup light hot wire.
so far, so good.
But moisture and corrosion had formed around the GROUND wire pins in the connector and the ground was "weak". So when the brake lights were sent power, the weak ground created a feedback loop that was "looking" for a better ground. The sensing circuit in the video switcher provided a pathway to ground for the brake lights and it exceeded the se sing threshold and triggered the video swap.
cleaning the pin and socket for the ground on the taillight connector solved the immediate issue, but I went ahead and soldered in a 3 amp diode at the "bulb end" of the reverse light wire to prevent any future feedback regardless of corrosion, etc.
Solved

Odd Piggy

Outstanding level of diagnosis, remedy, and preventative intervention.