ABS Fault !!!!!

[Ricky22buk]

My 2002 S8 (D2) is due its annual MOT but the ABS light and triangle light are on and I can't get them off. I'm a little confused to say the least and I'd very much appreciate anyone who has any knowledge to chip in.

My VDCS reads the fault as.......

00301 - ABS Return Flow Pump (V39), and the Ross Tech website suggests possible causes are fuse(s), wiring / connectors to the Return Flow Pump, or indeed the pump faulty itself.

My main reason I'm confused here is that I can reset the lights with my VDCS and while the car ticks over or even if I rev the car they won't ever come on, but the minute I start to crawl forward both lights come on again at about 10 mph without even touching the brake pedal. In my own mind the fact that I can reset the lights suggests to me that it isn't an electrical problem, as I assume they wouldn't go out if it was.

1. I have checked the 60A ABS fuse in the boot of the car, and I have also checked the two ABS fuses in the drivers side footwell, and both the 25A and 10A fuses are ok.

2. I have taken the plug off the ABS pump and the connections all look clean. There is a yellow wire with a red band which gets a permanent 12V when I try to start the car, so again, I'm assuming that the fuses and relays are all working fine to give me that.

3. I have checked the 4 wheel sensors and they seem to be functioning correctly.

Googling the fault people say the module attached to the Bosch ABS pump can give trouble, but again, why can I reset my lights if it had a fault ? I also think I read online somewhere that the ABS pump runs for a few seconds on start up just to allow the ABS module to confirm the pump is operational, but if this is true I don't think my pump is turning at all, and if it was the case why does the lights not come on until I start moving the car ?

Confused and not are what to do next. Can anyone enlighten me please ?

Thank you !

[Architex_mA8tey]

I've had a fairly major series of issues on a D3 I drive (which are now fully resolved I'm pleased to say) related to ABS pump and wiring issues.
The pumps themselves can suffer from being exposed to heat over many years from being close to the engine & manifold, which then causes the electronics in the unit to get dry joints and then you will find either intermittent or regular faults (often of many varieties) reported. The best remedy for that is to replace the ABS unit with either a new or secondhand one. If replacing with a second hand one then make sure the code numbers on your Old ABS unit are matched exactly by the incoming one, and don't separate the 2 parts of the unit, they should always remain together as hey are coded together in "pairs" that are specific so you can't mix and match.

I checked my abs sensors on each wheel and swapped them diagonally to see if the fault(s) moved but no change. Then myself and Mkoneman (James) stripped back each abs wire from the main Abs unit/ECU to each sensor, one at a time.

What we found was disturbing to say the least. Some of the cabling appeared brittle - the outer casing had turned hard and had cracked and in some places flaked away from the wire inside it, and because they abs wires are twisted pairs, this meant that wherever this happened, wires were occasionally touching and this then threw up a fault. In the end we replaced every abs wire from unit all the way to the sensor.

I have written to Audi as I am concerned about "dodgy or poor quality wiring" that perhaps was substandard having been used and wanted them to know in case this issue affects any other cars or braking systems. We also discovered that 2 sets of wires had been factory wired the wrong way around which could potentially be disasterous if the abs system engaged braking to the diagonally opposite wheel. We used the Audi wiring diagrams to ensure we had got the final solution correct and then the whole system tested ok and worked ok - I have also notified Audi of this at the same time but am not holding my breath for any action as the car is a 2006 early FL D3

Any ways all I can recommend from this experience is that you eliminate things like sensors by swapping them diagonally and then continuity test each run of abs wiring and if all that checks out ok then turn your attention to the abs pump & ECU combined unit, it may well be that the dry solder joint syndrome has hit your D2 as they are very similar, in which case you'll need to try and locate a reasonable second hand unit with the same coding, or send the original unit to BBA reman to see if they can fix it (they test and fix units and give them a lifetime warranty if they are fixable) but even that will cost you about £200 or so

[Ricky22buk]

Sounds like you have had your fair share of trouble to buddy. Thanks for your reply !

My mechanic plugged his snap on diagnostic reader into my car and made me drive the car slowly from standstill. He showed me the four graphs of the four speed sensors and they all looked identical, so I'm assuming that although that's what gave you the most trouble, I don't think that's where my fault lye's. When I turn my ignition on, the two lights in question light up as they should and go off again as they should. But when the car starts moving the come on permanently and have to be reset with the VCDS. So on that note :

1. Could the ABS pump and ecu module combined give my fault ? I assumed that because I could reset the fault lights and they didn't go on again until the car actually started moving that I could rule out an ecu module fault, and ABS pump failure....... I assumed that the lights wouldn't reset if I had those faults. In fact I thought for that very reason I could rule out all of the electrics?

2. Does anyone actually know if the ABS pump does run for a few seconds on start up to allow the ABS module to confirm the pump it's operational ?

I just cant get my head round this, and don't want to spend money unnecessarily until I can satisfy myself I'm working in the right area.

[Architex_mA8tey]

Originally Posted by Ricky22buk

He showed me the four graphs of the four speed sensors and they all looked identical, so I'm assuming that although that's what gave you the most trouble, I don't think that's where my fault lye's. When I turn my ignition on, the two lights in question light up as they should and go off again as they should. But when the car starts moving the come on permanently and have to be reset with the VCDS. So on that note :

1. Could the ABS pump and ecu module combined give my fault ? I assumed that because I could reset the fault lights and they didn't go on again until the car actually started moving that I could rule out an ecu module fault, and ABS pump failure....... I assumed that the lights wouldn't reset if I had those faults. In fact I thought for that very reason I could rule out all of the electrics?

2. Does anyone actually know if the ABS pump does run for a few seconds on start up to allow the ABS module to confirm the pump it's operational ?

I just cant get my head round this, and don't want to spend money unnecessarily until I can satisfy myself I'm working in the right area.

No mine wasn't any of the abs sensors themselves, it was a combination of the wiring issue and the abs ecu which i ended up changing. the replacement is now heat shielded to hopefully prevent any future issues from heat damaging the soldering in the ecu.

It really does sound to me like you would need to replace the ecu/abs unit, because if the sensors are reading correctly and the wiring is ok (I would still test continuity in case of the issue I highlighted) then it only leaves the pump and ecu combo which may need a speed signal from the wiring and sensors before it shows up the fault that may be inherent in the ecu.

I would get the ecu off the car and send to BBA reman and see if they can test it and fix it personally otherwise you'll be going around in that same circles that I did

[IT]

I had to change an ABS pump on a D2 once, and only once. Its a fairly rare occurrence to be fair.

The ABS sensors all connect to the ABS ECU in the plenum chamber. I would be checking this for any dampness as matter of routine as any damp in there and you'll never get anything consistent.

The pump itself is slave to the ECU, and relatively dumb, but does contain a little bit of circuitry. If this isn't giving the expected readings / outputs it could be the cause of your issues. It doesn't surprise me at all that you have to get moving before the ABS systems wakes up and does its checks fully as most of its input are from wheel sensors and steering wheel which are all idle at standstill.

I wish I could confirm my symptoms at the time matched yours, but I can't be that confident.

Its worth noting there is a basic settings for the ABS system. It's likely documented by ross tech and involves jacking the car up, and having each wheel be rotated while the ABS pump locks each one up in turn. Running that process might give you more clues as to what is actually at fault, but it might render the car more undrivable....

Changing either the ABS ecu or ABS pump are relatively simple tasks if you can find an exact part match. Changing the pump will require a brake fluid change/bleed though.

Mine was a 2000 year S8 that I had to change for reference....

[moltuae]

Had to have a new ABS pump on my (2002) S8 a few years ago. My symptoms were a little different I think though. I would randomly get the ABS warning light, usually after driving for a good 20 minutes or more. I could immediately reset it (by turning the ignition off-on) and it would usually stay off for another 20mins or so. If I recall correctly, it would also behave like there was a sensor issue, occasionally triggering the ABS under light braking. The fault become more frequent, putting the ABS light on even on short trips, at which point I booked it into the garage, where they diagnosed an ABS pump.

[I am a daisy]

http://forum.a8parts.co.uk/showthread.php?t=11278

[Mossyboy1978]

Originally Posted by moltuae

Had to have a new ABS pump on my (2002) S8 a few years ago. My symptoms were a little different I think though. I would randomly get the ABS warning light, usually after driving for a good 20 minutes or more. I could immediately reset it (by turning the ignition off-on) and it would usually stay off for another 20mins or so. If I recall correctly, it would also behave like there was a sensor issue, occasionally triggering the ABS under light braking. The fault become more frequent, putting the ABS light on even on short trips, at which point I booked it into the garage, where they diagnosed an ABS pump.

Hi there - I'm getting the same problem as Moltuae - could you advise how much it cost to replace the ABS pump as this may need to be looked at.

Thanks

[moltuae]

Originally Posted by Mossyboy1978

Hi there - I'm getting the same problem as Moltuae - could you advise how much it cost to replace the ABS pump as this may need to be looked at.

I really can't remember to be honest. It was a few years ago now and I don't seem to have an invoice for it (the garage is a customer of mine, so I think the job was probably done as part payment for what they owed me). I do remember it was fairly expensive but not eye-poppingly expensive. Probably in the region of £400-500 (+ labour) if I had to guess.

[donp38]

Interesting reading.

I have a squelch noise form the ABS pump when depressing the brake peddle.
Have bled/changed the fluid today.
No air in system at the wheels but wonder if there is an VCDS ABS system bleed procedure?

Squelch sound is still present at ABS pump.

Anyone?