Brake, ABS, and DSC lights come on randomly

I have a 2000 323i and from time to time the Brake, ABS, and DSC lights come on but, then when I cut the car off and get back in the DSC and ABS light will be on but they disappear after about 20 seconds. This has been happening since I bought the car in april. I haven't had any problems with stopping the car but if I slam on brakes really hard all 3 lights will come on. I looked in the owners manual and it says if the ABS, DSC, and brake light come on then the car has a brake system failure. I have noticed that the car does need brake pads, and the steering wheel shakes when slowing down(which may mean it needs new rotors also). What do you think?

I'm not sure what you expect to hear. If your oil light was on and there was a low level on the dipstick, would you ask if you needed something other than replacing the oil? Your car is telling you that something is wrong with the braking system, and shot pads/rotors would definitely account for that. You'll still be able to stop the car as long as the rotors and what's left of your pads can make contact, but if you put off replacing them then soon it'll be metal on metal and you'll warp your calipers as well, which will significantly increase your repair costs. Keep ignoring it and you'll lose your brakes altogether. Since you need properly functioning brakes to safely drive the car, get it done asap. The wiki has a few links for mail order parts (~$300 for four sets of rotors/pads/sensors), or you can try your local indy or stealership.

This could be something as simple as a wheel speed sensor causing the problem. The problem is determining which one. If one of the wheel speed sensors quits reading the stability control system and anti-lock system can't function. That's why you get the warning lights. The shaking steering wheel COULD be rotors but it could as be an issue with a tire or worn suspension bushings or loose wheel bearings, etc. Do you feel pulsation in the brake pedal? Sometimes warped rotors will cause the pedal to pulsate as the brake pads are pushed back and forth. The question is somewhat irrelevant since BMW recommends replacing the rotors every time you replace the pads. However, I don't always do that. You just need see how bad the rotors are worn before you decide. I doubt the lights are being triggered by the pads and even the rotors are not likely. It's much more likely to be an electronics problem (wheel speed sensor, abs computer/pump, etc.). I think BMW dealers can check to see what triggered the lights but I am not sure if the independent repair shops have access to the necessary equipment. I'd pull each wheel and check the sensors to make sure there is nothing obvious (gunk on the sensors, loosely mounted sensor, etc.). You DO need to find out why it's vibrating too. None of the conditions that could cause it to vibrate are good in terms of safety. Good luck.

Todd

Mine have randomly turned on and as described by H. Desmond, turn off when I shut the car off, or they will turn off about 20 sec. after operation. It seems worse after rainstorms, but I could be mistaken. My mechanic had changed my brakes and rotors about a year ago, and checked them recently to find nothing wrong with them. Did you find out what caused this?
Thanks,
DW

has either of you disconnected the battery lately? i put my terminal back on snug-ish, but not tight, and it caused weird electrical issues.

No I have not touched the battery since it was replaced ~ 3 years ago.

Yup this is classic. You may have a faulty speed sensor, but the trifecta usually means your abs module is shot. Unless you are under warranty, DO NOT go to the stealer for this. There are many places online where you can buy a repaired unit with core exchange. This happens somewhat frequently on the aging e39 which seems to use a similar abs module.

Originally Posted by la528it

Yup this is classic. You may have a faulty speed sensor, but the trifecta usually means your abs module is shot. Unless you are under warranty, DO NOT go to the stealer for this. There are many places online where you can buy a repaired unit with core exchange. This happens somewhat frequently on the aging e39 which seems to use a similar abs module.

It's much more common for it to be a wheel speed sensor than the ABS module on the E46.

Originally Posted by KrisL

It's much more common for it to be a wheel speed sensor than the ABS module on the E46.

Does that result in all three lights firing up christmas style though?

I have heard nothing but good about these authorized bosche repair facility with lifetime warranty:

http://www.bba-reman.com/

or you can repair them yourself, some guidance for a similar module is here:

http://www.volvoforums.org.uk/showthread.php?t=7414

basically the solder cracks and needs touching up

Originally Posted by la528it

Does that result in all three lights firing up christmas style though?

Yes.

Originally Posted by KrisL

Yes.

Fair enough. If you have a code reader, you could figure out which one it is, or you can follow the bare knuckle DIY path:

http://forums.bimmerforums.com/forum...d.php?t=600452

For us it is typically the front right that fails. Often you can see the small unit busted open with debris inside.


hope this all helps!

Originally Posted by la528it

Fair enough. If you have a code reader, you could figure out which one it is, or you can follow the bare knuckle DIY path:

http://forums.bimmerforums.com/forum...d.php?t=600452

For us it is typically the front right that fails. Often you can see the small unit busted open with debris inside.


hope this all helps!

All of that info is in the E46 Wiki, by the way .
http://www.bimmerfest.com/wiki/index.php?title=BMW_E46

This has happened to me before, and I used some some electrical connector spray to clean a wheel speed sensor. That worked that time. While I have not got around to checking anything yet[ will do that when I get home from work], I am bothered that the brake light is red like when I have the e-brake on. I think, but am not sure, that this was the case last time. I have read that when all three lights come on that they are all yellow. Am I in trouble here?

Originally Posted by KrisL

All of that info is in the E46 Wiki, by the way
http://www.bimmerfest.com/wiki/index.php?title=BMW_E46

Unfortunately, the wiki doesn't give the pinout for the E46 (which is slightly different than the E39 apparently), so to flesh out the solution for the E46 owners, I just opened this thread today:
E46 ABS control module harness wheel sensor pinout for the ABS/BRAKE/DSC bi trifecta

I bought a 04 325 xi with 121.500 on it last week. I test dove it for an hour around san francisco and had no problems. I then take it skiing last sunday and got a horrible vibration during acceleration under load. I also got a hard pull to right when i hit the brakes at speed. This pull was hardly noticeable during test ride yet i practically jumped laned when i hit hard at 75mph. I took the rig to my local Performance car shop Wednesday and they aligned the wheels and balanced the tires. Vibration gone and pull gone. Then last night, i get the ABS System fail light. I had noticed something weird a couple times with the right front. It seems to lock up and let go a couple times in the snow. Crossing fingers its that sensor. ps i am new here to this forum guys. Love it thank you!

Originally Posted by rawbspear

Crossing fingers its that sensor

The quick test for the hall effect sensors takes only about five or ten minutes, and you don't even have to lift the car or unbolt anything.

All you do is disconnect the harness and test the four sets of holes, one set for each connector.

For the E46 pinout, look here:
E46 ABS control module harness wheel sensor pinout for the ABS/BRAKE/DSC bi trifecta

The test procedure is here:
- How to diagnose the BMW ABS BRAKE DSC/ASC trifecta (1)