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BMW 840 Car Repair Questions and Answers

Question: 1994 BMW 840Ci mileage: 83,000. Hi, I'm the unfortunate owner of a BMW 840Ci, with an ABS problem. On starting the engine the ABS carries out its usual test and both the traction control and ABS lights go out. As the vehicle accelerates away and reaches above 5mph, both lights immediately illuminate and stay on. The fault can sometimes be cleared by switching off the engine, restarting the engine and then counting to 30 before engaging reverse, then reverse the car with full left hand lock on the steering wheel! The car will then drive away normally without either of the ABS lights illuminating. If however either of the rear wheels are spun, i.e. on gravel, then both lights will immediately illuminate and stay on. The car has been into the local BMW dealership for diagnostic checking, where they informed me that the pump relay was faulty. This has been replaced to no avail (and also the memory reset). They are now talking of requiring to test the car further for up to a day, at $85 per hour, just to find the fault! Prior to sending in the car initially, I removed all four wheel sensors and checked each of their resistances, which were all comparable. Although one on the left rear was found slightly bent due to stone damage, it was easily straightened. All four wheel segment rings were also cleaned up and in good condition. Any positive advice of tests that I could carry out would be greatly appreciated, before breaking the bank. Thanks in anticipation.

Answer: Your problem probably lies in one of the four wheel sensors for the ABS. There is a better test than the resistance check you tried. Unplug each of the wheel sensors. Spin the wheel segment rings and check for AC voltage at the sensors. You should have between 1 to 3 volts AC if the system is operating properly. Also check to see if you have a slightly loose wheel bearing that is allowing the segment ring to contact the wheel sensor.

Question:1998 BMW 840Ci mileage: 89,000. I have been experiencing problems with my check engine light. I have had the engine codes looked at and it was diagnosed as the 02 sensor. So, I have replaced it. Since then, I have also replaced all of my spark plug wires and my breather tube. I am currently at a loss. The light comes on about every other day and when it does come on the engine loses acceleration power and shutters lightly. It is drivable but the problem is very noticeable. It seems to me when it all goes wrong the fuel mixture is off so the engine over compensates and is either letting too much air in or it is letting too much fuel in. Any Suggestions? What do you think is the next best step?

Answer: Rescan the computer for fault codes. If no trouble codes appear and it still has the same symptoms the computer or ECM could be malfunctioning sending the wrong mixture to the injectors.

Question: 1999 BMW 840Ci mileage: 87,000. I have a question regarding my driver side power window system. About two months ago, the window started acting up. The symptoms are: 1. Whenever I tried to close the window, it always stopped in the middle. I have to try to press the power window button several times in order to fully close my window. What caused this problem? Is it the switch going bad, the control module or the motor? 2. There are also times when I could not even open or close the window. I have to wait several minutes in order to do anything with that window. 3. Where should I start to diagnose the problem?

Answer: From what you describe, it sounds like you have a control module that is going bad.

Model / BMW / 840

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