ABS ASC Lights On

The ABS unit is in the same place in the 850i / csi. I find that removing the headlamp provides easy access. it's just one screw for the cover and four 17mm bolts. Only takes 5 mins and then you have lots of access space to get to the ABS pump. After lots of experimenting, about a month ago, I found the connector to the pump to be a good culprit for intermittent ABS and ASC lights.

Zitat von arnie;82996

The ABS unit is in the same place in the 850i / csi. I find that removing the headlamp provides easy access. it's just one screw for the cover and four 17mm bolts. Only takes 5 mins and then you have lots of access space to get to the ABS pump. After lots of experimenting, about a month ago, I found the connector to the pump to be a good culprit for intermittent ABS and ASC lights.

Removing it completely or just removing the back bolts and flipping it over/forward? I ask as I know the lower front headlamp adjuster nut will be siezed in place and forcing it off will break the plastic loop off the headlamp base (happened on the otherside).

Therefore completely removing the headlamp is the last thing I want to try.

I meant the whole headlight assembly, including its carrier and lift motor. This attaches to the front frame by 4 x 17mm nuts. You need to raise the headlight to access the front two nuts. You'll need a ratchet and a 17mm socket on a medium extension. You can leave the wiring harness connected and just move the assemby out of the way to rest on the wing, making sure you don't drop it. Else, disconnect the wiring plug as well and place the headlight assembly somewhere safe, whilst you do the work.

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Yes, I'm sure it's the ASC actuator! The other actuator is for the cruise control which acts on the main throttle body. I don't have cruise, so I only have the ASC actuator. The ASC system has its own secondary throttle body which is used to reduce engine power.

Ah! I see you have deleted the post I've answered, that will be a bit confusing!

Zitat von Timm;83007

Yes, I'm sure it's the ASC actuator! The other actuator is for the cruise control which acts on the main throttle body. I don't have cruise, so I only have the ASC actuator. The ASC system has its own secondary throttle body which is used to reduce engine power.

Ah! I see you have deleted the post I've answered, that will be a bit confusing!

Tim, sorry, I'd deleted it because I noticed I'd read the part wrong on the EPC.

However, do have any more info on this ADS actuator? Occasionally, I do get the ASC light just on its own. I see that there is about 11 volts on the two pins of the plug that connects to the actuator, but is doesn't appear to move.

I'm even more confused now, from your posts above, I thought you had an 850i/ci/csi! Only the 840i/ci has the ADS (auxiliary throttle position motor or ASC actuator).

If you do have an 840i/ci, then the ADS is a simple motor and gearbox that pulls on a Bowden cable, which in turn moves the auxiliary throttle butterfly. Just like the other servos (cruise control etc), it also contains a potentiometer that reads the position of the Bowden cable (being connected to the final gear).

Normally, the motor is stalled against the end-stop by applying 12V to it, the secondary throttle butterfly is fully open. When power is disconnected, the Bowden-cable return-spring pulls the throttle butterfly towards the closed position, in turn rotating the actuator motor and moving the potentiometer. When the desired throttle position is reached the motor is energised and the closing movement stopped. The motor is then controlled to servo the throttle butterfly to that position.

The usual failure is not of the motor, but of the potentiometer which fails to show the correct servo position. The actuator is checked at switch-on, it will close and then open the throttle butterfly and an expected change in potentiometer resistance is expected.

Fairly different on an 850CSi

Ok I took the headlamp out, then had to take a rubber boot (part of the intake going into, not from, the airbox) out. What I found underneath looks nothing at all like the images above, different pump, different connector and 2 relay's. I have had 2 failed relays on this car already, Im hopeful that these ABS pump relays are the the root cause of my current failure. Took some photos will put them up later.

I cleaned everything and used silicone grease on the connector, but my Carsoft cannot read the OBD1 850 (but works fine on a OBD1 740) so cannot reset the code. Lights were still there on the dash.

The ABS/ASC fault light should reset itself once the fault is fixed. May take a few starts.

Zitat von Timm;83017

I'm even more confused now, from your posts above, I thought you had an 850i/ci/csi! Only the 840i/ci has the ADS (auxiliary throttle position motor or ASC actuator)....

Yes, I have a Csi, which has been off the road for a year or so. I now (after my 728 was written-off) also have 1999 840ci, with lots of problems.

Ah! That explains that then, an E38 man as well........

Zitat von Timm;83017

....Normally, the motor is stalled against the end-stop by applying 12V to it, the secondary throttle butterfly is fully open. When power is disconnected, the Bowden-cable return-spring pulls the throttle butterfly towards the closed position, in turn rotating the actuator motor and moving the potentiometer. When the desired throttle position is reached the motor is energised and the closing movement stopped. The motor is then controlled to servo the throttle butterfly to that position.

The usual failure is not of the motor, but of the potentiometer which fails to show the correct servo position. The actuator is checked at switch-on, it will close and then open the throttle butterfly and an expected change in potentiometer resistance is expected.

Tim, Thanks for the explanation. I see that there is 11v to the motor, but I see no movement when connecting or disconnecting the connector plug. The ADS throttle seems open, and the bowden cable not very tight, There's also a position switch or sensor on the throttle itself. The motor unit only has 2 connections, so its potentiometer must be for "internal-use-only"?

Will need to investigate futher. It's now also put my ABS out of action. I must have nudged something when replacing the spark-plugs, since I can no longer even communicate with the Bosch ABS controller (Carsoft thinks it's now a Teeves unit!) But this was after erasing the original stored error codes.

However, with new Bosch FR78x plugs the engine runs brilliantly now, compared to before. The hesitation has gone and the starting is quicker. I did follow your guide and found some oil leakage into the spark-plug bores and also a number of plugs were hardly hand-tight, so I think some oil was comming out the other way too. One coil was loose with its nuts not fully screwed down. The last people to look at that was a main dealer. The vibrtion is still there, though at exactly 1150 rpm with a very narrow window of +/- 50 rpm, but at every other speed it's very smooth, so I've not yet figured that one out. Idling, too, seems perfet now, at exactly 700rpm.

The rocker covers are made of magnesium and the paint is flaking off, leaving a dark-grey powdery surface. Seems like the paint starts out brilliant silver and then yellows with heat and age. I need to see how to repaint them when I change the seals.

Yes, the potentiometer is separate from the actuator (being on the throttle butterfly), I was getting confused with CC actuator for a moment there! When I get a chance, I'll see what the actuator on mine does when I unplug it......

Just to note that after cleaning all the contacts and soaking the relays in WD40, the day after I did it and since (ok just 2 days) all lights are out and everything is working correctly with many starts and drives.

Now that I have said that, I would almost bet that tomorrow all the lights will be back on again.

That's good news!

It is worth saying that a number of these type of problems can be due to low battery voltage (although not in your case). Where the battery voltage is low, certain motors will just fail to work correctly (especially in this cold weather). This includes pumps (ABS, windscreen washer etc), actuators (door locks, ASC). Especially where a car has sat for a month or two, a good, charged battery is a must.

I have so much sympathy for anyone dealing with this problem; what hasn't been mentioned so far in these two parallel threads is the possibility that the fault lies in the ECU itself. It's a bugger, but it has to be faced in some cases.

I wasn't the first (nor will I be the last) to ignore the ECU. Naturally, we all want to find another cause due to the cost involved in a new replacement; somewhere on here is a detailed account of how to isolate the fault in this unit on the 840Ci. It's definitely worth a read if you've got the time and are at that stage where you are pulling your hair out because you've just changed something (a relay, wheel sensors, cleaning the contacts... etc) and it looks like "the" fix, only for this moment of euphoria to be followed within minutes by the dreaded "oh, no"....

The car will run OK without the unit if you decide to disconnect it. There's a great company in Kent who know how it works and will fix any faults for a reasonable price, re-seal it and send it back with a 2-year guarantee. Usually the problem is internal condensation and associated corrosion of the contacts on the circuit board. My part was sent to them in October 2007 and it hasn't put a foot wrong since then:
Bosch ABS/ASC ECU Version 5.0, Part No. 0 265 109 022. The total cost then was £108.50 plus VAT.

They are at www.bba-reman.com.

I had a faulty ABS unit and BBA -Reman couldn't repair it - fortunately a helpful colleague on this website from Germany had a second-hand unit and this did the trick - Just to underline how supportive this website community is!

Yes, the pictures I've seen of 840ci ABS ECUs show that the circuit boards arre not "conformally coated" (lacquered) against moisture (unlike the engine ecus). Additionally, the electrolytic capacitors usually reach their lifespan after about 10 years and some of these control the voltage supplies. Not difficult to replace these and as long as the CPU is not fried, then the ecu can usually be cleaned and repaired.

The 740i facelift models also suffer from ABS/DSC failures due to the control module. In this case they are bolted onto the ABS/DSC hydraulics:







Unfortunately, BBA-Reman has failed to repair either of mine, nor have they managed to repair other members units on the 7-Series board. They cost £500 plus coding from BMW!

Zitat von Timm;83067

That's good news!

As suspected the first start and the first 15min of driving today (after 3days no use) and both lights on. However once they went off when the car was restarted, stayed off all day and systems worked correctly.

Definitely looks like the relays are seizing up and road use/heat frees the again.