Help with ABS problem please

[gunman]

My S2 has been layed up now from May. I drove it last night for the first time since that. The brakes seemed very spongey and the ABS light stayed on. This evening I hooked the car up to VAG-COM but I'm getting no response from controller on the ABS Unit. I can scan the engine and Airbag systems fine. I'm fairly sure that any time I ran a scan in the past that the ABS unit was fine. I have checked fuse 31 which was fine but I replaced anyway, also took the plastic over off the ABS pump and replaced both relays. Started the car and the ABS light went out but every time after that it stayed on. Still cant communicate. I can hear a ticking sound when I try which seems to be coming from behind the stereo area.

My wife has told me that the last time she drove it back in May that the ABS light came on after a couple of miles, stopping and restarting put it out again for another couple.

Anyone any ideas where to start with it?

Sorry, nearly forgot, car is a 95 ABY avant.

Cheers.

[Cottis]

Had this with an old CQ a few years back. From memory I think the actual ABS switch was sticking. Oh hang on, is yours an ABY? Don't think they have switchable ABS. Sorry, ignore that then.

[Mikes2]

Normally, if the lamp isn't coming on until you've started moving, there will be a sensor fault.

Other components like the ecu, pump or relays will trigger the lamp before you start to move

[gunman]

Light comes on with ignition, never goes out.

[ManiacuV6]

What's the version of VAG COM ? I can connect to ABS unit and I have the same unit on my 94 Competition.

[gunman]

Not sure about version but its genuine Ross tech. Updated couple months back, don't think vagcom is at fault, I think whatever's wrong with abs is stopping comms.

[ManiacuV6]

Is not a easy task but you can measure the K and L wires from the connector ( 2+2) to ABS's ECU ( under the rear seat).

[sidrick]

With those symptoms my first check would be the fuse on the abs relay under the dash.

[gunman]

where would that be? I changed the relays at the pump, didnt know theres one under the dash. It did go out once, if it were a fuse could this have happened?

Does anyone know if an abs ecu from an 80 tdi would be the same as the S2?

Cheers

[Mikes2]

later cars didn't have that relay. I'd reckon it will likely be the ecu under the rear seat or fuse 31

[twoqu]

Some modules seem to be more sensitive to low voltage than other. Did you charge the battery up prior to starting it after the lay up? If not, try charging the battery to see if it has an effect.

[chezz]

From my extensive nightmares with ABS, I would advise you to totally rule out the sensors first...components such as the ABS pumps etc., rarely fail.

[fzr phil]

what about the diff lock switch, any problem there?
that will/ should switch off the abs and cause the ABS light to come on when activated. can't remember if it should reset when ign is switched off/ on though.
Good luck sorting it
Phil

[gunman]

It's not the fuse, I checked and replaced that. I thought the ABS ECU was in the right panel in the boot on the avant, is it not just the diff lock under the seat?

I would have thought that if it were a sensor that I could still connect to the ecu with vagcom?

[chiefmechanic]

Abs

I would bleed each wheel. Only needs a couple of pumps on each one. Check the relay with a fuse on the top of it in the auxiliary relay rack(if you have one).
Electric valves in the abs may have a little moisture on the seat and could have rusted or debris from brake system ( rubber) that's stopping it close tightly. Bleeding might move it. Any of the discs getting hot may indicate which circuit is at fault.
I would change the abs as a last resort.
Brian