Glow plug light flashing/ESP/ABS light on...


Registered User
Hi everyone. I've been a long time reader here but I finally managed to get myself into a mess that I can't get myself out of. I have an '03 Audi A6 C5 Avant 2.5TDI Quattro. Here's the issue with what I did and what happened:

A week ago I decided to order the P21 Osram LED bulbs to make my reverse lights look "cooler." They came, I removed the regular bulbs, put them in and nothing. They didn't work. Disappointed, I put the old regular bulbs for the reverse back on and everything was back to normal. And THEN...

My brake lights stopped working when I would hit the brake. Not even the one on the tailgate worked. Shortly after, my glow plug light started flashing and the ABS and ESP lights came on. I saw this thread here: so I figured something happened with my P21 bulbs for the tail lights/brake lights. I bought two brand new ones (the correct ones) and put them in. They work when I turn on the lights, but still no brake lights when I press the brake pedal and the one on the tailgate doesn't work as well. So I then replaced the brake pedal switch. I bought one as they're cheap and fitted it today. It didn't fix a thing. Still no brake lights.

My car doesn't have a loss of power. Everything is normal bar for the lights that are on the dash and the lack of any lights in the back working when I hit the brake pedal. What could it possibly be? Any help would be appreciated.


Registered User

I found a friend who has the VCDS. I scanned and got the following two codes:

-Code 00526 when I went into Engine Control Module: Brake Light Switch Implausible Signal Intermittent.
-Code 00741 when I went to to the ABS Control Module: Brake Pedal Monitoring Implausible Signal.

So, I didn't know what to do. I went back and checked the bulbs. They were fine. I bought yet ANOTHER break light switch and replaced it. Nothing again! So finally I did a bit of research and people were saying that it might be the brake light/switch fuse. But nobody ever said which one it was. So which one was it?! It wasn't listed in the diagram for my fuse box or owner's manual. So I found it online. It was fuse #13 in the side fuse panel that's easy to access. It's a mini red 10 amp fuse and lo and behold, it was blown. D'oh!

So if you ever get the following problem, my advice is to do the following:

1. If you obviously have any rear tail light bulbs out, replace them. Replace them in pairs since they're cheap, and make sure you not only get the right ones but also install them properly (make sure they click into place, etc). Especially the brake light bulbs which have the ba15d fitting unlike the others. If that doesn't work...
2. Check the fuse for the brake lights/brake switch! Mine was fuse #13, but in your model it may be a different fuse located elsewhere. Find it and check it and obviously replace it. If that doesn't work...
3. Replace the brake pedal switch. It's about a 30 minute to a one hour job and a little fiddly because of access, but it's not difficult at all. This should fix your problem once and for all.

If you had the same problem as me, these three things will probably get you home and dry 95% of the time. If you do these things and you're still don't have working brake lights and abs/esp lights illuminated on the dash, then you'll need to go to a professional shop or mechanic where they'll just have to do some further digging and look for the problem, which will inevitably be more expensive than the quick fixes I pointed out above.

I hope that helps anyone who runs into this! I may have unnecessarily bought a few extra bulbs and two new brake switches which probably cost me around $50, but at least I learned my lesson.