ABS lights

Car is a 2001 Passat and the ABS light is on and the brake light flashes. At first, I could not communicate with the ABS controller. New controller and we can communicate, and it's showing an open or short to plus on the Right front speed sensor. I unhooked it and checked resistance and it matches the other side. Beyond that, I don't know how to go about checking these. It's a two wire sensor, so can I watch voltage on the sensor while I spin the wheel?

I did a full scan and a few of the modules showed no communication with the ABS controller. Would the speed sensor cause this?

Lastly, would the Right REAR wheel bearing being bad loose cause this thing to wack out?

QuickTD said:

Sensor is a simple variable reluctance type (magnet with coil around it). It will produce a weak AC signal when the wheel is rotated. They sometimes get covered in rust/metal filings but can be hard to access for cleaning without destroying the sensor, they get rusted in there...

Check the coding of the replacement module, it has to be coded to match the other modules (trans/engine type etc.) or it will not communicate properly.

Any recent wheel/brake/hub repairs that may have lead up to this?

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I don't know how to check coding.

I have pulled the sensor (it came right out) and it looked fine.

The light was on before I did the CV boots, so that wouldn't have been it.

Or the reluctor wheel on the CV joint gets rusted to a point where it won't read correctly.

ABS sensors will generally throw one of two codes

Electrical (I think this is the one you have) where there is an open in the circuit that prevents the ABS ECU from reading anything from the sensor. Diagnose this kind of code by inspecting the connection, the wiring, and the resistance across the sensor compared to the others.

Mechanical - This kind of code will set when the car is in motion - the circuit checks out fine, but that wheel does not register a speed that jives with the other wheels - this will most likely start to occur when the car is coming to a stop - the bad wheel will drop to 0 ahead of the other three.

It sounds like you have the first kind of code - electrical - if you are good with the resistance of the sensor compared to the others, then the next thing I would check is the wiring - I would get ahold of the wiring diagram showing the 8 wiring colors and connector positions for the four sensors, and then ohm out each wire.

If the Sensor is in fact good, then you probably have a bad wire or terminal, or an off chance of a bad ABS ECU.

It sounds like you have the first kind of code - electrical - if you are good with the resistance of the sensor compared to the others, then the next thing I would check is the wiring - I would get ahold of the wiring diagram showing the 8 wiring colors and connector positions for the four sensors, and then ohm out each wire.

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I think this is where I need to go on this because it is an electrical code and the resistance matches the other side.

Again, confirm your coding is correct first.

Second, did you put a used or new ABS unit in?

I dont know how to confirm the coding is correct. Can I change it with VCDS? I think it was a used module.

So if I plug in the old controller and read it's coding, I can plug in the new one and change it to match? The car will be back Tuesday for the rear wheel bearing.

Thank you for your time helping me with this.

Crap. I think that is why we replaced it. Forgot that part.

So, assuming that it won't communicate, I checked Rosstech site and I didn't see anything specific about setting it up. Just general stuff on coding.

If you have the latest software and go to coding, as you hover your mouse over the code area your available coding options will show up. That is a good place to start.

Also, using a used ABS module could throw you off as I have seen some which will show a bad ABS sensor with no way to fix it. In other words could be a bad ABS module.

I'm so happy I could poo. We sent the original ABS controller off to BBA Reman in Taunton, Mass. and I have FINALLY gotten around to putting this controller back in. (No fault of BBA, just me being busy) I fired it up and immediately saw the ABS light wasn't on! I did a full scan and saw the codes then I hit "clear" and did another scan but the codes were still popping up.

UGH.

Then I remembered that I hit "clear" not "Clear all DTCs". Obviously I need to use my VCDS more often.

Cleared the codes, ran another scan and all is well. Drove it around the block and all is still well.

I'm so happy I could poo.