Intermittent Brake Warning Alarm

I'm having a strange issue with my '06. It started a few weeks back and has now happened three times. The red "BRAKE" warning light will flash. Accompanied by three beeps. It then shuts off. This is not the pad wear or ABS light. The same warning light that is tied to the hand brake. The light functions properly with the hand brake. The brake fluid level is fine. I've inspected all four corners and see no leaks or worn pads. Pedal feel is firm. There is nothing in VCDS indicating an issue. All three times have been at high elevation, in cold conditions, while climbing a mountain pass. Maybe the brake fluid level sensor is going out? Anybody have an idea of how to troubleshoot this?

How long since you flushed the brake fluid? Perhaps there is a little water in it if it's been a couple of years.

If you have the late master cylinder, replace the pressure switch on the bottom of it, and see if that fixes it. Assuming you are certain you have no leaks or loss of fluid anywhere.

Ditto on the brake fluid question. How is the tension on the E brake handle when down? Pull your rear calipers to ensure free movement & that the baring brake cable ends are properly engaged.

oilhammer said:

If you have the late master cylinder, replace the pressure switch on the bottom of it, and see if that fixes it. Assuming you are certain you have no leaks or loss of fluid anywhere.

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How do I tell the difference between early and late master cylinders? I will triple check for leaks. The reservoir is full, so it's not showing signs of leaking. Pedal feel is firm and hand brake function is solid. The brake fluid is old. I haven't touched the brakes in this car since I purchased it five years ago or so. New shocks and rubber went in a few months back. I took a good look at everything back then. I pulled each wheel and inspected everything again after the first time the alarm went off.

If it has the pressure sensor in the bottom, it is the one with the pressure sensor in the bottom.

Just take a peak. I think the FTE brake master cylinder has the sensor, the Ate/Teves system does not.

The sensor is to detect a difference in pressure in the two master cylinder circuits, and if it is off, it will send a signal to the cluster to turn the red light on.

*I think*, as I am going off of memory of the A5 platform. You may need to replace the master cylinder, but I think that sensor is available by itself and you can try that first if you want.

edit: the part number I get in ETKA is 5G0-698-459 "repair set for brake light sensor". Looks like a little MAP sensor stuck in the master cylinder body itself.

Thanks. Cheap enough to throw that part at it and see what happens.

Well. I have an earlier car. No such sensor on my master cylinder.