ABS pump started to run all of the time, ABS stopped working

[Aaron]

I took my 1991 BMW 525i out in the snow to play, as it is one of the most balanced and fun to drive cars I've ever driven in the snow. Well after a few runs where the ABS was working fine, the ABS light came on and it stopped working. I get home, turn the car off, and the ABS pump won't stop running (Which it's never done before). I let it go for an hour before I finally unplug the battery. I plug it in again a few days later and the ABS pump immediately starts running again.

Any ideas?

I'm going to check the brake fluid level and clean the ABS wheel sensors (common E34 problem), but I fear this won't fix it but should be done anyways.

[Emc209i]

When I was a kid, my folks had a minivan that had an ABS module under the van near the catalytic converter. It would go wonkers whenever driving it in wet weather or snow. The pigtail o-ring had rotted out and was allowing water into the metripack which in turn led to a short inside the connector. I have no idea why Ford would have thought it was a good idea to put the module down there. Anyway, water alone won't short a connector, you need salt to disassociate in it to form a strong electrolyte. Snow, salty roads, driving hard... I'd check the connector at the pump. If it continues to act up, you could unplug the connector there instead of disconnecting the battery - until you find the problem and hopefully fix it. You can drive with that module unplugged, you just won't have emergency braking - which you don't have now if it won't shut off.

Obviously the module thinks that one or more wheel(s) is losing traction continuously.

[Aaron]

I actually did just that, disconnected the plug, and have been driving it that way. The plug/modulator are in the engine bay, secluded, and then covered, so it was extremely clean and corrosion-free. I'll probably clean the wheel sensors this afternoon, hopefully that helps.

[Aaron]

I just got done cleaning the sensors and checking brake fluid (Which was good). Not too difficult, although the rears required moving the calipers out of the way. I didn't think they were that dirty, though the left sides were dirtier than the right front and rear. Surprisingly everything in the wheel wells was fairly clean, corrosion free, and appeared to be in good shape. Surprising for a 262,000 mile car that gets zero maintenance aside from oil changes every 10,000 miles.

Plugged the module back in, and to my amazement it didn't kick on. I started the car and everything was good again. Since the rear wheels were in the air I spun them up to 85mph or so then got on the brakes, and I felt the modulator modulating like it should.

My brake pads looked brand new, amazing considering I've put 20,000 miles on them since checking them last, and the brake linings warning is on constant. I decided to look into that, and found the PO decided to just cut the wires of the front sensor instead of removing it properly. He of course cut them right at the sensor, so no room to solder them back together. I ordered a new sensor, $8.99, and that'll be in tomorrow. I jumped the leads together and sure enough the brake linings warning went out. Sweet!

[Aaron]

Less than 2 months later, I pull out of a dry parking lot and the ABS light comes on, and upon turning the car off the pump stays running. Crap.

In a week or two I'll clean the sensors again, although I doubt that's it this time, and I think a sensor is going bad. The weather hadn't been that bad, but it's worth the shot to clean them.

[The Dark Side of Will]

Have you tried reseating the wheel sensor connectors at the module?

A friend of my g/f's had a 2004 Hyundai with a rear O2 sensor code (NOT a catalyst efficiency code). It wouldn't pass inspection with the CEL on. I did nothing but reseat the O2 sensor connector and the ECM connectors and the code went away.