a4avant99

Did not bother to read the code. The switch is $9.XX including tax.

Part number 3B0-945-511 changes to a 1K2-945-511-RDW which I stock and it runs $8.75.

The length appear to be not adjustable. Looks tougher.

The car is a 2004 3.0L quattro. I bought it in summer. The Engine light came up a few weeks ago. The code is P0421, supposed to be passenger side catalytic converter or a spark plug. I cleaned the code a few times, and it just came out a week later. I went ahead to replace the spark plugs yesterday. Evidently, the last time the spark plugs were replaced (when doing timing belt), only the driver side spark plugs are replaced. Car has ~125K, and its passenger side spark plugs are still the original! I suppose that is the cause for the engine code. But today, the ABS and ESP lights are on.

The ABS and ESP lights do not appear when car starts (just come up and go away as normal). They come up the same time I release brake pedal after engaging transmission (both R or D). Could it be something I messed up yesterday while doing the spark plugs? While doing the spark plug, I took off the coolant tank that is above the ABS unit. I checked today. The only thing that I may damage is a wire plug to the ABS unit just aside the coolant sensor plug. I did not find anything abnormal. Any input? Thanks.

SloopJohnB@mac.com

Anything is possible but you need a vag-com to check out the abs module, the electronic bit that attaches to the abs pump. Chances are it's simply coincidence and you need a new module.

Prices have gone up for repairing an abs module, used to be $45, now it's $100 or so.

http://www.autoecu.com

The above repaired my 2K4.2A6Q ABS module...however their website now doesn't even list it.
Give them a call...all you do is remove your module and send it in.


See here:
http://www.autoecu.com/asi-AUDI-PASS...FU1x5QodsisYDQ

Which indicates autoecu.com DOES repair ABS units. Just contact them.

PS: I removed and replaced the ABS ECU on my 2K4.2A6Q in about three hours...had to remove left wheel and fender liner and a couple bolts were tricky...if I had to do it again I might be able to do it in an hour or so. IT was plug and play; I didn't need to reset anything with VAG-COM. VAG-COM was only used to diagnose the issue.

4Driver4

Agreed...or he bumped the module when doing the plugs. Once the wires break a wiggle or jiggle and turn the ABS light on and off.

a4avant99

Last time using wag-com was 4-5 years ago for my A4 B5 ABS light, resulting in an ABS rebuild. Never bothered me later to hook a computer on (a generic code reader just did all engine light related job fine). I will check the code next weekend. But would the code be there before starting the car? I do not have the lights before releasing the brake pedal after engage transmission.

I will first unplug and plug all the wires around the coolant tank beforehand to make sure there is no broken wire. I tend to believe (hope) I just damaged a wire.

Likely the philosophy is that, while the brake pedal is released, the ECU begin to communicate with the ABS/ESP system. The light are on due to a mission signal. If it is the ABS unit like the case for my A4 B5, the ABS and brake light would blink. This time, there is no brake light. If the ABS/ESP lights are not related to my spark plug job, I tend to believe one of the speed sensor is broken (so light come up before moving). But when the functionality of the sensors are checked? Does the ECU check them before cranking the car, or the ECU does not check the sensors at all, and just begin to read them while the car begin to move?

Thanks

4Driver4

Check the codes first.

bigdadi

A simple $12 fix ... brake pedal light switch

https://www.audiworld.com/forums/sho...ighlight=meaty

For P0421 CEL : check out www.bigdaddiesgarage.com

SloopJohnB@mac.com

U lucked out...it was new abs module for me.

a4avant99

I will go ahead to replace the brake switch ---- brake light is intermittent.

First, I went to press the brake pedal without starting the car. The brake lights are OK.

I then started the car. Once I press and release the the brake pedal, the ABS/ESP lights came up, and then no brake light when I press the brake pedal.

I then turned the car off, and still no brake light when I pressed the brake pedal.

Brake switch problem confirmed?

a4avant99

Fixed by replacing brake light switch