ASC + ABS Lights on

I'll try going in through the wheel-arch, then. While I'm at it I'll probably replace the plastic lining as it's cracked in a few places and no-doubt lets water spray through.

I'm also getting ABS and ASC lights on now. It started happening when the car hadn't been used for a while, so I suspected electrical gremlins. Then became more and more frequent, now they come back on most of the time within a few seconds of the lights going off after the ignition is switched on.

I had the system plugged into a BMW DIS computer, and here are the results (click to enlarge):

Does this seem familiar to any of you guys? I'm wary of the stuff about "pressure-acumulator", isn't that only fitted to the 850 (known as the brake bomb)? It doesn't specify any difference between 840 and 850, just "8 series cars". The part about the pump earth connection is interesting though.

Oh mine has the pink relays but I've already tried swapping those out.

Cheers
Paul.

Nice scan-tool. what is it? Ah, BMW DIS- Wish I had one.

Anyway, that's the fault I used to get intermittently, more so with cold weather and/or damp mornings. Being able to operate the ABS a few times on gravel etc seems to have cured it. So, perhaps it may have been ageing relay contacts or a sticky motor. However, now I get left wheel sensor showing up most of the time. It will usually go away after a long drive, though, but back the next time.

(I also hadn't used the car for a while).
However, I'm pretty sure it's not a permanent failure of any valve or motor, because, as I said, it was intermittent.

The ABS pump is activated as part of a built-in test as soon as the car's speed gets above 5mph. This is also when the system checks to see if it gets 4 wheel sensor readings, which are roughly the same. This is why, if there's a problem with these, the lights will come on as soon as you pick up speed. Other system tests, for open circuits on valve coils etc, are done on first power-up, and if the lights go off, after starting the engine, these check OK.

I think that the ABS unit is not located in the best of places and if the fault is intermittent, it most likely as a result of bad electrical contacts or dirty motor (see Tall Tony's pics). First check-point should be the two relays.

If all checks out, finally have a look at the ECU in the passenger sill, and again see Tony's former post on this.

The possible causes listed on your screen-shot are about right and should be checked.The fault you listed is not connected to the brake-bomb, which, incidentally, all 8-series have.

The wheel sensors also have a habit of going bad with intermittent operation. This is due to the thermal stresses they see on the wheel hub, near the brake discs, and also possible eventual ingress of water. These are similar to cam-shaft or flywheel position sensors, which also fail regularly.

Good luck!

Thanks for your input Arnie. I'll have a look at it the next time I get a chance.

Zitat von arnie

The ABS pump is activated as part of a built-in test as soon as the car's speed gets above 5mph. This is also when the system checks to see if it gets 4 wheel sensor readings, which are roughly the same. This is why, if there's a problem with these, the lights will come on as soon as you pick up speed. Other system tests, for open circuits on valve coils etc, are done on first power-up, and if the lights go off, after starting the engine, these check OK.

The strange thing is that the lights always come on for 5 seconds or so, then go off. But sometimes they come on again after a few seconds, before I have even released the handbrake. So it seems it's detecting some problem, not related to wheel rotation, after the self-check lights have gone off. Other times the lights will stay off until I start driving. Occasionally the lights will stay off and the ABS & ASC work as normal (i've tried them and they do work when the lights are off).

if the lights sometimes come on briefly again before driving-off, then it must be sensing some other non-latching fault. The voltage supply to the ABS system is continually monitored and is controlled through an over-voltage protection relay. Can't remember which number it is, but its in the main LHS fuse/relay box. This may be one more thing to check.

They don't come on briefly, what I mean is that they go off a few seconds after switching on the ignition (as they should), but then they come back on a few seconds later and stay on until the ignition is switched off. All this before moving off.

Before you spend too much time trying to resolve it have a look at the solution my local garage came up with...Couple of posts previous to this one. Sounds like my issue was slightly different as they were on all the time.

This might be barking up the wrong tree, but the ASC does link with the engine management, although one would presume this would only light up the ASC lamp in the case of such a fault.

Otherwise, it still could be a faulty OVP relay or low battery/alternator voltage (<8.5v).

However, I think your main "return pump" fault is related to the motor, its electrical connections or its drive relays. Most likely, if you sort this problem, the other may go away.

Finally got some time and nice weather to have a look at this. I took the ECU out and swapped it into another 840, and it works fine in that one. So I think it's safe to say the ECU itself isn't the fault in my case.

I removed the K94 relay and checked for the presence of 12V at pin 30 -- pass on that. Shorted the switched terminals of the relay, and no sound at all so it seems the pump has either failed, or there's a wiring fault between the relay and pump.

My next step is to check the wiring in the wheel arch, hopefully it's just abraded through as suggested by the diag tool. In that case I'll use the repair kit available for this, otherwise I'll check the voltage actually getting to the pump (including ground connection) and if that's good then it must be the pump itself.

The joys of E31 ownership

Following all the ABS/ASC lights that I'd been having, I was gong to check the ABS pump and its motor, but before getting round to doing that, the "fault" seems to have disappeared. Just driving the daily car for 2-3 weeks with the lights coming on seems to make it go away. I've had this fault appear now three times over two years, and each time was after not having used the car for a few months.

At first I thought these "faults" were related to damp, cold mornings, but now I suspect that was just coincidence. I am beginning to think it might be something like electrolytic capacitors in the controller, which might be failing, and which are being revived just enough, through regular use.

You may well know the method but might be worth having a gander at Terry's entry in the Tips and Tricks section. At least its worth a go!

My latest update is that I checked the wiring and all appears OK. So strongly suspecting the pump now -- was going to try removing it via the arch but no such luck as the torx bolts are pretty corroded.

Have refitted the arch lining for now and will probably try to source a known good pump before I go any further. They come up on ebay.de quite frequently but I'm waiting for one from a seller who accepts PayPal as doing an international bank transfer is a PITA.

Will update as and when I know more. No hurry though, as I'm not hugely concerned about having no ABS, and no ASC+T could be considered an upgrade

i seem to have a similar problem, although its just my asc light that comes on after around 3-5 mins of driving. i have changed the ecu for another and it is still does the same. BUT also my abs is not working, but the light does not come on, bulb is fine as it comes on with the ignition. any ideas anyone???

That is a strange one. Best first step is to get it hooked up to a diag machine to read the fault codes -- a GT1 or MoDiC is ideal, but even a more basic system like CarSoft should at least give some indication.

thanks for the advice, looks like its my final option!! will let you know the outcome, cheers

ASC light - fixed it?

Hello Smudge2031!

I have the exact same problem as you with the ASC-light. Not usre if my ABS is broken though, haven't pushed it that hard...

Did you read the fault codes and did you find the problem?

/Hannes

For what its worth, my #2 car has had an ASC light with a mind of its own for the past 3-4 years. Comes on whenever it feels like it. Sitting in my garage idling, on the road, at a stop, whenever. And it comes on, every time I drive the car.
This past weekend, on a whim, I changed both the filters in my ASC+T system. Sucked out most of the tired old Pentosin and replaced with new. Simple job overall. Now, two days later with many road trips, no more ASC light. Too early to say the filters and the grungy Pentosin caused the problem but am cautiously optimistic.
Worth a shot for those of you still experiencing the random ASC light problem.