VW Passat brake warnings

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Sat 6 Nov 2004 10:07
VW Passat brake warnings - Morris Ox
One for thos of you who know how brake warning systems/fault code readers work.

Have a 98R Passat 20V which has occasionally been displaying warning lights/sounding buzzers for the ABS (orange light) and the whole brake system (red light).

I've had the ABS and the brakes emergency checked and there's no problem (that was obvious from driving - no increase in pedal effort, no reduction in ABS sensitivity). Local spannerman thought it might be dirty sensors and cleaned them, but the fault returned. Independent VW garage ran a fault code reader but couldn't find any fault with the warning system.

These warnings sound regularly and while the ABS warning will go with a simple dab of the brakes, the main brake warning keeps coming back unless you pull over, switch off and then start again.

Anyone got any idea what the problem might be and what the (cost effective) solution is? I've just spent useful sums of money having both the cambelt and the head gasket changed (it's a 20 valver!) so I'm not looking for another big bill.
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Sat 6 Nov 2004 20:44
VW Passat brake warnings - Aprilia
If you are handy with a digital multimeter then I can e-mail some data on speed sensor resistances and output voltages etc. Also pump motor resistance etc. etc.
The only way to fix it is to carefully diagnose the problem - 'poke and hope' is expensive!
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Sat 6 Nov 2004 21:55
VW Passat brake warnings - Morris Ox
My worry (and experience) is that a VAG dealer won't carefully diagnose the problem. They'll do a couple of routine checks, which won't locate the problem, and then take the easy and expensive way out by replacing the parent system rather than subsidiary components where the problem might be.
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Fri 25 Nov 2005 18:24
VW Passat brake warnings - old man
Aprilia,

I realise this post was made quite a while ago, but I wonder if you still have the data for speed sensor resistances etc?
My 97R Passat TDI has an ABS fault which exhibits itself at very low speeds and light brake pedal pressure, which involves a 'twang' from the front of the car and slight feedback through the pedal (pedal resistance momentarily decreases, as if the ABS is working). No braking system faults were registered when the car was connected to vag.com, and no warning lights are showing. I suspect it may be a fault with one of the front sensors but have checked the condition and cleanliness of these and they appear to be OK. I would appreciate any technical information you may be able to provide.
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Sat 26 Nov 2005 02:07
VW Passat brake warnings - Alec
You can use the VAGCOM to read the output from the ABS sensors while rolling slowly back and forth.
That's how I found a dirty one that was causing the ABS to operate as the car came to a standstill.
Rgds
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Sat 26 Nov 2005 11:04
VW Passat brake warnings - Aprilia
Front and rear sensor resistances should fall in the range 400-2300 Ohms. Best to check this by unplugging the ECU connector and checking at the connector terminals (in case of wiring fault).

Spin the wheel at 60rpm (i.e. one turn per second, approx) - you should have a signal of 1V a.c. from front sensor and about 0.4V a.c. from rear.
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Tue 6 Dec 2005 12:29
VW Passat brake warnings - old man
Thanks for this information. Having found the connection for the ABS sensor (just behind the rubber grommet in the wheelarches) tested both sides with the meter and found no voltage output from the nearside front.

After removing the sensor and cleaning off the accumulated crud, problem solved.

Cheers.
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