Intermittent brake warning on start up.

[Audi Gav]

Now that the colder weather is here if I start the car and it doesn't catch immediately I get the red brake warning light up. As soon as the engine starts running the alarm disappears and if I press the 'Check' button everything cycles though to "OK".
This only ever happens when starting the engine from cold and then only once in about every 8 to 10 starts and always when the engine hasn't caught immediately.
When the alarm is up pressing the 'Check' button points to a fault in the ABS system. I tried heavy braking on ice the other day and ABS seems to be fine. I assume anyway that a genuine ABS fault wouldn't just clear.
I seem to remember a similar thread (which I can't now find) that suggests a common problem in the diesels that the drop in volts when cranking can cause a spurious alarm. Certainly ties in with the symptoms I have but wouldn't mind some confirmation from members. Original battery and car now 3yrs old with 44k on clock.
I would assume not urgent to get it fixed either if it is the voltage drop causing it.

[kite]

A8 tech is the man in the know, your correct about a voltage spike, I think there was a relay fitted to stop this or a wire moved from around the master cylinder
You could check to see if your battery is low.

[vma99r]

Hello,
I had the same thing happen to mine last year, (2005 2.5 tdi)
It turned out that Audi did a modification to fix the problem but the original owner did not bother to get it fixed under warranty, so I had to pay the bill ---- £198.78 ---- Before that I was told that if I changed the battery that may solve it but no good. From memory it is to do with voltage drop when the car has been standing for a while. In the end it was driving me mad so I had to get it done.
If it helps I could give you a list of the parts as they listed them on my invoice.
Cheers Pete.

[a8 tech]

http://www.vwaudiforum.co.uk/forum/showthread.php?t=56355

[Audi Gav]

Thanks guys. Only query I have A8Tech is that thread you pointed to mentions low fluid level. My symptoms are identical with the exception that pressing the check button indicates an ABS problem. It seems a bit much of a coincidence not to be a voltage glitch though.

[a8 tech]

Well I would check the cold cranking voltage as this is when the fault occurs, it will appear to crank ok but just a slight cranking rpm drop will pull the voltage down sufficiently for the spike so by bypassing the X relief circuit to the dash the problem is resolved.
The repair kit including the relay is easy enough to fit and takes no more than 1 hour.If you need the part number pm me your email and I will send them to you with the instructions

[Audi Gav]

OK. Thanks again a8tech for your help. May just live with problem at the moment and sort it out when I get time or it gets more persistent. One last request, can you post the link again (attachment 4556). The link is no longer valid in the thread you sent me. Cheers.

[Codestud]

I also had this problem on my S Line 170 Avant, which started during the cold weathers in January.

The fix, as mentioned is a relay because it's something to do with an electrical glitch.

Fix cost me about £160 from an independent VW/Audi specialist.

[Kaysvay]

yes, I have the same issue on my tdi blb in hot or cold weather. Battery is perfect.
At least I know it's just a voltage spike. No worries.