Noise and modulation on low speed stops

[Bimmerman325i]

Sorry for the bump, but my car decided to have this same problem on the way to work this morning. Did you ever solve the problem? It's never done this so I'm a bit confused; I didn't even know the ABS system worked until now, usually I can lock up a tire under braking. I've got a driver's school coming up soon and I definitely can't have this problem linger! Please Help!

[AndrewBird]

I was just remembering, back when we did all that work to your car in Portland, one of the connectors in the engine bay for one of the sensors got melted a bit because it hadn't gotten plugged back in. I wonder if it is shorting out? Have you checked all the wiring to and from the sensors yet?

We also should check the rear sensors. If the fronts were covered in stuff, the rears are likely to be the same way.

[Jand3rson]

I'll have to check those, because now it's back, and doing it worse than ever. Andrew and I are going to see if we can't track down the problem this weekend.

Autocross is in 2 weeks, and I can't race like this!

[DaveSmed]

So I can't say for certain, but I think I *might* have fixed it.

A month or so ago when my fuel pump took a shit, the first thing Crivvy told me to check was the fuel pump relay, one of those 3 in the block next to the strut tower. He also said to maybe try reversing them, and see if it does anything. Well, I think I left them reversed, and while I was just getting gas, I swapped them, and now the problem seems to be gone. One of them also wasn't even all the way seated, so who knows.

Interesting that one wasn't seated, but none of those are the ABS relay. On your car, it is located under the dash above the ABS module clipped on to the bracket the module mounts to.

Those three relays are the main relay, which powers the fuel pump relay, injectors, DME and ignition coil. (May vary slightly based on i vs e engines)
The fuel pump relay which powers the fuel pumps (imagine that.) And the O2 sensor heater relay.

[Jand3rson]

So I can't say for certain, but I think I *might* have fixed it.

A month or so ago when my fuel pump took a shit, the first thing Crivvy told me to check was the fuel pump relay, one of those 3 in the block next to the strut tower. He also said to maybe try reversing them, and see if it does anything. Well, I think I left them reversed, and while I was just getting gas, I swapped them, and now the problem seems to be gone. One of them also wasn't even all the way seated, so who knows.

[gearheadE30]

My car did this a bit but there was a fuel injector retaining clip stuck to one of the front ones that was causing it ;). I have no idea how that got there...

At any rate, I think that it is on the sensor end of the ABS system. Have you checked them with a scope yet? Is all of the wiring good, including all connections? It almost sounds like one of the sensors is failing and causing the sensor to get a flat reading.

[Bmjpv]

abs

I had this at low speed too. Fixed it by finding and replacing the ABS counter on the axle. It can only be the counter or senor for at the corners. I hope my repair helps with your hunt . Joe

[Jand3rson]

I also noticed something else about this problem today, it only seems to do it under very low speed light braking, such as in parking lots or rolling up slowly to a light. If I really jam on them, or if I'm braking hard around a corner or something, they're fine.

[PiercedE30]

I believe the three are the main, fuel pump, and abs (?). Not sure though. Either that or unplug the plug on the pump and try it.

[Jand3rson]

Is that one of the 3 big square ones under the hood, near the strut tower?

[PiercedE30]

Pull the ABS relay?

[Jand3rson]

I need to update this again, after finding some new things out. I went and talked to a couple of guys at German Master Tech, a local shop run by a couple of guys that are BMW Master Techs, and ran this issue by them. They told me that it's very unlikely that it's a stuck caliper, that wouldn't be causing the ABS to freak out.

What they reccomended was pulling the sensors and making sure there wasn't a bunch of crap all over them. When I pulled them, there was tons of stuff on them, the passenger side was so bad, I had to scrape it all off with a razor blade. I got everything back together, and it did it right when I got to the end of my street, and then several more times while I was out driving.

Has anyone else had this issue, and how did you fix it? I've checked most of the things suggested here, and I'm still not any closer to getting this fixed. I don't know much about brakes, please help!

[diegom6]

Once my ABS module arrive, I will try it and see what results give...so far it's still not working with the inspection of the module and clean up f the relay.

[PiercedE30]

Maybe try rebuilding the calipers. It may even just be a caliper piston that is gunked up.

[Jand3rson]

It started doing it again tonight. :(

So is it more likely that the sensors are bad/out of whack than the caliper being bad? I know I've never changed them (the sensors).