Electrical gremlins cause phantom brake warning, help please !

Hi there,

I've a bit of a strange one here, just recently my 58 A3 1.9 TDI has begun showing the 'brake fault, drive carefully to nearest workshop' warning on cold starts. When it does this the engine won't start. Turning the key a couple of times clears the error and the car drives perfectly.

The car has just been serviced (in fact the first time it did this was when I was driving to he dealer for the service !) they've checked the brakes and all is well, although all pads need replacing soon-ish, and they say that there are 'numerous faults stored in memory concerning Voltage Supply -no comms'. They've said that they suspect that the voltage supply relay might be on its way out but can't be sure.

Unfortunately they haven't given me any specific fault codes to investigate further.

So, before I get hit with a long investigation, costing a fortune, is there anything I can check for myself to try and narrow things down ?

Could it be something as simple as the battery being past its best ?

Is there anywhere in particular I should look for loose or corroded connectors ?

Where does the Voltage Supply Relay live and is it expensive to replace ?

Thanks in advance for any help you can offer, sometimes these beasts are just too clever for their own good !

Richard

Get the car scanned for faults with vcds.

We needs to know what the exact problem is and where it originates from, especially with electrics it's better to pinpoint the source.


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Ok, so I caved and gave in to the main dealer as I don't have access to VAGcom.

They investigated and found two relays T15 and T30 which were misbehaving. Apparently they must have been arcing for some time as they seemed 'quite burned'.

All-in cost me £250 which, while not exactly cheap, is a heck if a lot less than a new ECU or ABS unit would have been so I feel I got off lightly.

Maybe this info will help someone else !

curious though, what do the T15 and T30 relays actually do ?

Answers on a postcard !

Terminals 15/30 basically are the electrical circuits for most if not all the modules etc, so are fairly important, tbh they should of just scratched the relay contact pins which usually fixes the issues.