Not another ABS Thread


Want to apologize for the long winded essay, just want to give as much background info as possible. I’ve posted this to other bmw/e30 forums and haven’t had much luck. Technically this isn’t for a spece30 car ('88 ix) but after reading some other ABS threads on this forum I’m hoping someone here has some knowledge that could point me in the right direction. Just going to copy/paste below.

Been struggling with this ABS issue on/off now for about a year, I’ve read many ABS troubleshooting forum posts/e30 electrical troubleshooting guide/asked local e30 mechanics and can’t seem to figure out the issue, so if anyone can share some insight I’d greatly appreciate it!

I’ve got a 1988 325ix (production date 11/87) with roughly 180k miles on it, bought it cheap, sight unseen, from someone who didn’t know what he had. Seemed pretty honest about the condition of the car…wish I wasn’t so trusting of people.

Anyways, it all started with the pesky e30 odometer gears being all worn out so I took the cluster out to repair them, upon putting them back in, I had noticed that as well as the 3 harnesses (Blue/White/Yellow) there were 2 sets of wires going to bulb harnesses not attached to the cluster. Got some new bulbs and of course my ABS light was on.

I know that for these cars there are 3 simple diagnostics with the ABS Lights; mine being “ABS Light comes on with ignition, goes out upon starting and comes back on at idle” meaning there is a wiring problem, bad ECU, or bad ABS relay or weak/bad alternator.

I started by pulling the overvoltage protection relay out of the car, the relay was bad (the internal fuse was blown) so I DIY’D a fix for it and checked to make sure it was working correctly - it was. Buttoned everything back up and the light popped on.

I knew power was passing through the relay so my next step was to make sure power was getting to the ECU. After digging around a bit in manuals/forums I found that on the wiring harness to the ECU (thanks to someone from this forum!)

Pins 10, 20 and 34 should be Ground
Pins 15 and 25 should read 14V
Pin 29 should read .69V

Everything checked out except pin 15 was reading at 1.5V. According to the schematics, Pin 15 is being provided voltage from the Alternator. Took my voltmeter to the back of my alternator and found that it was only outputting 1.5V. Pulled it, got it bench tested and determined I needed a new voltage regulator. Popped a new one in and it was outputting the correct 14V. Went back to Pin 15 on the wiring harness and that too was outputting the 14V.

Once again, buttoned everything back up, went to start the car and…light still came on.

At this point I went to the pump. Pulled both relays out and checked to see if they worked with the “click” test (aka hooked them up to my battery and heard it audibly clicking) as well as checking the diode in the valve relay. everything seemed to check out so I’m ruling those as functional. I thought maybe the pump itself was bad so I sourced a used one off ebay from someone who promised me it worked when it was in their car. (did this twice so I actually have 3 ABS Pumps and 2 valve relays and 2 pump relays…).

I’ve replaced all 4 wheel speed sensors on the car because I just love throwing money at this thing and wanted to eliminate those as a problem, two of them I knew for sure were bad.

ABS ECU was the next thing I had not looked at, after checking continuity between all the pins (34) on the harness with the position they landed on, grounds going to the correct place and voltage coming into the pins that were constant or did not rely on the ecu, I confirmed that the wiring in the car seemed to be correct.

My car came with a black label ABS ECU (Bosch 0265105011), Ive tried two other black labels which did not work, an orange label (Bosch 0265103012) and finally a green label (Bosch 0265105019)

According to realoem the green label ecu should be compatible with my car and the car idles for a good 40-50 seconds before the light turns on, while all the other ECUs turn on within 10-15 seconds or just stay on upon start up. The only reason why I tried the orange label was because the pump I have installed came from a car with an orange label, the previous owner suggested I try that. The pump part number matched with what realoem had for my car.

I feel like i’ve exhausted all of my options, or I’ve been so wrapped up with all this troubleshooting I’m missing something so simple.

Any help would be greatly appreciated!



be sure the fronts sensors are installed correctly, they are left and right. check inside the big abs plug going into the computer, I found a broken wire inside one once.


Bought them new from fcpeuro, they both had the same part number but physically looked different. Any way to tell the difference, they seemed to really only fit one way. Also would that cause the light to turn back on even when the car isn’t in motion, I thought bad sensors only trigger the light while moving.

I’ve checked every pin on the ecu harness for continuity, they all checked out.