ABS light is on

A while ago I removed both front struts in my iX to replace the upper strut mounts. (These are different from regular E30 struts, but the basic principles are the same.) After putting it all back together, I began having a problem with the ABS, where the ABS would engage at very low speeds, like when coming to a stop. Since the only thing I had changed since before the problem started was the front struts, I figured it was one of the front wheel speed sensors not getting a good signal at low speeds.

So today I pulled the connectors for both front sensors and tested the resistance. They were the same, which makes sense since they both were fine before I messed with the struts. I suspected something in the teeth of the hub that the sensors read. I cleaned out all the teeth and pulled some greasy gunk out of the right side. I also cleaned off the sensors.

After putting everything back together, sure enough, no more ABS pulsing, which is great. But now my ABS light is on. Any ideas what could be causing this? I'm suspecting something with the sensors rather than the computer, unless the computer just happened to act up at the moment that I was working on the sensors.
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Dave
'91 325iX

If you turned on the ignition while the sensors were unplugged, for sure the computer set the warning light. That light may be difficult to reset. There is a special tool that plugs into the 20 pin connector and has some buttons on it to connect various pins and an internal circuit, and the ignition switch is involved in the process. It took two different techs and about half an hour to get mine to reset. They had to dig out the instruction book for the tool and repeat the process a couple of times.

Bob in Lake Havasu

Are you sure the wiring isn't broken internally? On my E46 I had the pad wear light on intermittently, flickering at times. The pads were pretty new, so no contact there. Checked the connector, nothing to see there either. Turned out to be the wiring broken, nothing to see at the insulation. Cut out a piece, soldered it together and it's still holding, no lights so far.



Edited 1 time(s). Last edit at 10/24/2013 03:26AM by Michiel 318iS.

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Bob in Everett
If you turned on the ignition while the sensors were unplugged, for sure the computer set the warning light. That light may be difficult to reset. There is a special tool that plugs into the 20 pin connector and has some buttons on it to connect various pins and an internal circuit.

Thanks. I actually have a SIL reset tool, but I don't think it does the ABS light. Anyway, I'm pretty sure I didn't turn on the ignition while the sensors were unplugged. Besides, I've confirmed that the ABS is in fact not working (did a skid test on my gravel driveway ), i.e. it's the system, not the light.

I'm actually fine with not having ABS, but I would like to know what's broken. (BTW, the iX uses a different ABS computer than the regular E30, and it's one of the least intrusive ABS systems I've run across.)

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Dave
'91 325iX

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Michiel 318iS
Are you sure the wiring isn't broken internally? On my E46 I had the pad wear light on intermittently, flickering at times.

I'm pretty sure, based on the resistance test I did at the connector. The sensors have a fairly long wire, so the connector is quite a distance away from the sensor. The resistance was < infinity, indicating a connection, and was the same on both sides.

My pad wear light is on all the time. Those stupid wires are always breaking!

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Dave
'91 325iX

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Dave_G

I'm pretty sure, based on the resistance test I did at the connector. The sensors have a fairly long wire, so the connector is quite a distance away from the sensor. The resistance was < infinity, indicating a connection, and was the same on both sides.

My pad wear light is on all the time. Those stupid wires are always breaking!

I'm not sure if the resistance indicated is the sole thing to consider here.
There may be wiring problems, the computer can't get usable data and shuts off with the dash light on.
If all of those check OK, perhaps new sensors are needed, or you will learn to live without ABS from now on.

Checking the '90 iX electric scheme, I figured out the E30 is not using Hall sensors, but magnetic coils (so no need for a power supply when testing). Have you tried reading the signal when rotating the wheel? Best would be to use a scope, but a DVM should read something as well (though not accurate) in the AC range.

The ABS on the iX E30's is one of the better I've ever had on that age of cars (both my E30's were non-ABS, true sports cars).

I have the same problem. Where was the break? How did you find it? I would like to fix it.

Bob in Lake Havasu

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Michiel 318iS
Checking the '90 iX electric scheme, I figured out the E30 is not using Hall sensors, but magnetic coils (so no need for a power supply when testing). Have you tried reading the signal when rotating the wheel? Best would be to use a scope, but a DVM should read something as well (though not accurate) in the AC range.

I haven't had a chance to check that yet (busy weekend!). I'm hoping to find some time to do that test this week.

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Dave
'91 325iX

Well, that was weird.

I tested all four sensors, found the one in the front right that was different, and confirmed by spinning the wheel that the resistance on that one wasn't changing. OK, bad sensor, and I ordered a new one. The next day I got a call back from the vendor saying that ABS sensors for the iX are pure unobtanium. Even BMW in Germany doesn't have them -- they needed to order some from their supplier, which could take months. But the vendor said they would charge me the same price, and I wasn't in a hurry, so I said fine, let me know if/when you get one in.

Not 5 minutes later I got in my car drive home, and the ABS light was magically out! (It was on when I parked the car.) I tested it on wet leaves in my gravel driveway, and sure enough, the ABS is working again. It's been 24 hours now, and it's still working. I guess I'll just leave it alone and see how long this lasts!

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Dave
'91 325iX

I didn't know the iX sensors would be different, only thing I know of is a low surface grip sensor and different software for the ABS. As the sensors are magnetic, I'd measure AC voltage when spinning the wheel.