ABS Troubleshooting

[davintosh]

My daughter got herself into a tight spot on a road trip last week and had to hit the brakes pretty hard. The car stopped without hitting the vehicle in front of her, so no body damage, but the front wheels locked up flat-spotting the front right tire and tearing a chunk of tread out of the front left, making for a nasty shimmy on the front end. We swapped tires front-to-back and it was able to make the last three hours to home ok, but it left me wondering why the ABS didn't keep the wheels from locking up. I'm reasonably sure the car has ABS; I can see what looks like the ABS hydraulic unit in front of and below the brake master cylinder, and I'm pretty sure these cars had ABS as standard equipment. I drove the car last Saturday and there are no warnings or other indications that there is trouble with the ABS system.

My daughter is back at school now, so the car is an hour away from me, but I'm looking to get my ducks in a row to do some troubleshooting when she's back at home in a weekend or two. What would be the first things to look for to figure out what went wrong?

[Uber E30]

Check to see if maybe the PO disabled the ASC and ABS

[davintosh]

Originally Posted by Uber E30

Check to see if maybe the PO disabled the ASC and ABS

What would be done to disable them? Pulling fuses, disconnecting modules, or... ?

[1996 328ti]

No warning lights on?
Odd. Maybe no bulb?

I just replaced an ABS sensor in my Mini.

[spidertri]

If you brake hard on a gravel road/surface does the abs kick on?

[davintosh]

Originally Posted by spidertri

If you brake hard on a gravel road/surface does the abs kick on?

I haven't tried that, and won't be able to for a while. Will contact my daughter & have her give that a try. And yes, there are no warning lights. Most of the other lights in the cluster are out also, and replacing them is on my list of things to do. Will check that bulb when I've got the cluster out.

[Uber E30]

Originally Posted by davintosh

What would be done to disable them? Pulling fuses, disconnecting modules, or... ?

Well my only experience with it is on an m52 but the throttle body boot gets replaced and you disconnect a plug, however if someone didnt know what they were doing its possible that they disabled ABS with it.



Yellow circle is the ABS plug, red is the ASC. What year is the car?

[spidertri]

I can confirm that if you unhook the ASC+T module from the engine bay both the ASC+T and ABS lights will turn on in the cluster. If you only remove the ASC+T throttle body, only the ASC+T light turns on in the dash.

[Uber E30]

Originally Posted by spidertri

I can confirm that if you unhook the ASC+T module from the engine bay both the ASC+T and ABS lights will turn on in the cluster. If you only remove the ASC+T throttle body, only the ASC+T light turns on in the dash.

For sure, but he isnt getting any warning lights at all, and he knows some other lights dont work as well. Im guessing most people that do the ASC disable will pop the light out of the cluster, if they disabled ABS then they could have easily take that out as well.

Regardless ABS didnt work, OP has ABS, so either the unit is disabled, not getting signal, or not getting power.

[davintosh]

Daughter was home for a short while tonight, so got the chance to check a few things...

Originally Posted by spidertri

If you brake hard on a gravel road/surface does the abs kick on?

Tried that; locked up. Top speed when hitting the brakes was ~25mph. No discernable pulse or other feedback from the brake pedal, just tires pushing gravel.

Originally Posted by Uber E30

Well my only experience with it is on an m52 but the throttle body boot gets replaced and you disconnect a plug, however if someone didnt know what they were doing its possible that they disabled ABS with it.



Yellow circle is the ABS plug, red is the ASC. What year is the car?

The car is a '98. Looking under the hood I can see the connector for the ABS pump, and it appears to be connected. I don't see anything that looks like the ASC plug you have circled though. The only thing going to that area of the fuse box looks to be the lighting wire harness.

When turning the key on there is no ABS light on the dash. Unfortunately, we've got severe thunderstorms rolling through right now (looks like it's midnight outside, and the sun doesn't go down for another ten minutes) and I have zero available garage space right now, so wasn't able to pull the cluster to check to see if the light bulb was there. Further troubleshooting will have to wait until she comes back in a week or two. :sigh:

[Uber E30]

If the ABS module is plugged in then my next step would be to take a voltmeter to the plug. If that checks out ok then I would buy new sensors.

[tiFreak]

if the ABS light isn't coming on I'd have the codes scanned since the light is probably commanded on. you'll have to either go to the dealer or an independent BMW mechanic though, they'll need to use the BMW-specific scan tool to check the ABS codes

[Rusky]

iv got a similar problem iv no lights on dash that's is no abs or asc come on but im sure the abs isnt working as iv tried the braking hard test the wheels just lock and there no o pedal pump to indicate abs is working and im guessing without abs there is no asc as on the e39 5 series

[Rusky]

checked sensor cable seems fine but couldn't remove sensor from wheel

[drummond07]

I just had the same problem with one of my front sensors (driver side). I used some spray oil to lubricate and finally got it out with vise grip pliers. I let the lube sit for about a week and continued to oil it everyone other day or so. The right one (passenger side) came out very easily. This didn't solve the problem (I don't think) since I can't get the code to clear. I read on bimmerforums that if the ASC/ABS lights come on and stay on, there is more than likely a problem with one of the control modules (if not both). I also read that these codes MUST be cleared with special code readers at BMW shop. I'm going to BMW shop and have them scan the code and tell me what's wrong. The local shop here (MPLS, MN) is having a special to read and clear codes for $40. I'll let you know what I find out. Good Luck!