Every morning when i start the car the ABS and ASC lights is on. I dont need to drive for more than a minute, stopp the engine, and start up again, the light are gone. Sometimes they come on while driving, but that is very rare. I have measured the ABS sensors , they are fine. The valves in the ABS pump was stukk , so i change the ABS pump. What more can i check?
ABS and ASC ligts comes and goes
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You might wish to check that the ABS controller in the left-hand door sill is dry. (I had a badly replaced windscreen that was letting water in and which flooded the controller. It started with intermittent faults, but by the time I found the cause, I had to buy a new controller.)
Also, in some cases, the internal (electrolytic) capacitors - there are three - can leak due to age and cause problems. They can be replaced if caught early enough before the printed-circuit board tracks become erroded.
One other thing could be battery voltage. If it drops below 8.5v, the controller will show a fault. Check the batteries, of course, but also check the connectors and ground wiring to the controller. A light spray of contact cleaner may help on the contacts of the large, 86-way connector on the controller. -
Zitat von TERMINATOR;93412
I had my windscreen replaced a few years ago, so i need to check this controller. Where do i exactly locate it ?
Check the ETM. One of the last pages has a module placement drawing.
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I've had a similar issue once on my first E24///M635CSi. Above 120km/h a small bump regularly set off the ABS light. It turned out to be a dirty ABS ring on one hub. So a purely mechanical issue actually. You may want to check if those are all ok. Dirt of heavy corrosion can cause the system to malfunction.
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Yes, if you haven't already done so, remove the wheel sensors and give them a clean. You'll most certainly find that they will have collected a lot of iron particles and this may hamper their performance. This would cause an ABS and ASC error whilst driving.
The sensors have stainless-steel bodies but the retaining screws and the mounting hole may be somewhat rusty, so a penetrating lubricant spray and some patience may be required to ease them out.
Check also the castellated sensor ring to see if it's clean, but it is hidden beneath the brake shield plates and these cannot be removed without first taking off the wheel bearing assembly. However, there are some slots where you can see through. A powerful torch light is a good idea.
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I have checked and cleaned the sensor rings , but the ABS and ASC lights still comes and goes....
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Mabe the ABS pump is shot.
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When exactly do the light scome on. When you turn the ignition key? ...or after you start the engine?... or after driving?
Some diagnostics would really help here.
It is possible that the ABS pump has a problem. This could be either with a valve or the motor unit.... but you say you've already changed that? -
Do you know which wheel is causing the issue?
What about the sensor itself? I had it on my wife's E39-523i.
Broken cable with intermittent contact has been the cause of it.
I have several used spare sensors available. -
Have you had your car read?
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My very similar problem was caused by dirty Pentosin filters. Because I have ASC+T I have a filter in the reservoir (replace this one) and one in a brass enclosure below the rad, This one is stainess steel and can be cleaned. Cheap fix if it works, maintenance if it doesnt.
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Zitat von Wuffer;93746
My very similar problem was caused by dirty Pentosin filters. Because I have ASC+T I have a filter in the reservoir (replace this one) and one in a brass enclosure below the rad, This one is stainess steel and can be cleaned. Cheap fix if it works, maintenance if it doesnt.
[INDENT]Good point, but that is not relevant to the 840Ci as the ABS/ASC-T is a self-contained, inetgrated unit that does not require the auxiliary hydraulic system (Pentosin fluid) to power the ASC, as on the 850i.
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If the problem is intermittent, it may be a wiring or bad-contact issue. However, I've always found that in reality, bad wiring or bad contacts usually tend to occur a lot less frequently than I imagined and often it's a real hardware fault. Therefore, I wouldn't completely discount the Control Unit. Once I had some starnge intermittent issues with another car and eventually found that the problem was due to a failed capacitor on the ECU.
New sensors, as you've seen are extremely costly. if you can borrow a Control Unit from someone then perhaps you can discount that completely.
However, with the ASC ligt comming on first, it could be an issue with the ASC valve circuit, as otherwise, the ABS light would come on at the same time, if it were a sensor fault.
It would really be useful to read some error codes, if you can.
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