Brake light warning on, but nothing showing on a scan. Any ideas?

[Phutters]

2004 allroad BAU.

I had a problem with an intermittently dicky wiper relay - sometimes too many sweeps on wash/wipe accompanied by a chattering from the relay, sometimes too few and occasionally one errant sweep when turning the ignition on.

I got a replacement from a breaker - identical part from another allroad, relay 603, part no 4B0 955 531E and fitted it this afternoon. The wipers now function as intended, but I have a different problem that I wasn't anticipating.

The first time I turned the ignition on with the replacement relay in, the yellow brake light bulb failure warning popped up in the DIS. It does this every time the ignition is turned on irrespective of whether I've got the old relay in, the replacement relay or no relay at all.

A scan at the local specialist shows bugger all. Everything is absolutely clear. All three brake lights work properly. I've re-seated the brake light bulbs and even swapped them for new ones. No change. The wiring to the brake light switch is undisturbed, as is all the wiring adjacent to relay 603's socket.

As a last resort prior to I don't really know what, I've disconnected the battery temporarily in the forlorn hope that the car will come to its senses and stop messing about when I reconnect it.

Has anyone got any bright ideas as to what might be causing this blasted light to come on?

Thanks

Pete

[Phutters]

Bumping your own post with a reply of your own is a bit lame, but for anyone furiously trying to help, disconnecting and reconnecting the battery after about fifteen minutes didn't change anything.

At all.

[zollaf]

sounds like an Audi being a blooming Audi then. my s4 beeps randomly telling me there is a bulb out, but not which one. they all work, all been cleaned, yet it beeps relentlessly.

[Phutters]

sounds like an Audi being a blooming Audi then. my s4 beeps randomly telling me there is a bulb out, but not which one. they all work, all been cleaned, yet it beeps relentlessly.

Thanks, Mr Z.

I can't see how replacing that wiper relay and this warning light and beeper can be anything other than an infuriating coincidence. Apparently the light also comes on if there's a problem with the brake light switch. If the switch had decided to act up, I'm assuming that a) the brake lights wouldn't work, and b) the fault in it would be picked up by a scan.

Are they reasonable assumptions, given that the brake light switch affects more than just the bulbs?

[zollaf]

yes, the switch will be a 4 pole switch, it switches the lights on and tells the ecu you are braking. but, if its the brake warning light showing i would check the fluid level first and be certain you dont need some brake pads.

[Phutters]

Sorted. Red faces all round. I'd dislodged the light control relay (no 393) and that was causing the problem.

Thanks, and I'm sorry I wasted your time.

[zollaf]