Rich98MRoadster
Newbie
- Joined
- Jun 17, 2026
- Points
- 3
Hi,
First of all, I'm a newbie to this forum (and any forum for that matter) so please forgive me if I appear unsure of what to say and where to post it.
The reason for this post is that I've been going around in circles for some time now with the ABS issue(s) on my May '98 built M Roadster and I'm hoping that someone out there can help get me off this roundabout!
When the dreaded light came on after a period of being laid up, I plugged in the OBD reader and got codes 51, B1 and B8, seeming to point to a hydraulic valve fault.
Not wanting to change the pump unless necessary I checked all the wheel speed sensors just in case the codes were wrong. No problems found with the sensors.
I then elected to try changing the ABS control module (5WK8 405) as they're cheap and commonly available on Ebay. So I've tried 2 different ones and both give the same errors.
I then bought a used (but supposedly tested and working) pump - it's the yellow label one for my car so a bit pricey but still a lot cheaper than a "new" one (no longer available on some BMW databases). I plugged it in, without connecting it to the actual brake lines, just to see whether the codes changed. They didn't!
I've since tried all sorts of combinations, disconnecting wheel sensors etc... and even disconnecting the battery between each change just in case the ECU is "remembering" the codes but nothing changes the codes.
So, I've come to the conclusion that either all 3 ABS controllers are faulty or there's a wiring fault.
I'm not sure what to try next. I've printed off the pin-out for the ABS controller connector - thank you to whoever put it on the resource pages, so I'm going to attempt to check the wiring.
I'm also tempted to open up one of the control modules too.
Am I missing something (apart from a few marbles - as I feel this is frying my brain)?
Thanks for taking the time to read this. Any pointers would be appreciated.
Richard
First of all, I'm a newbie to this forum (and any forum for that matter) so please forgive me if I appear unsure of what to say and where to post it.
The reason for this post is that I've been going around in circles for some time now with the ABS issue(s) on my May '98 built M Roadster and I'm hoping that someone out there can help get me off this roundabout!
When the dreaded light came on after a period of being laid up, I plugged in the OBD reader and got codes 51, B1 and B8, seeming to point to a hydraulic valve fault.
Not wanting to change the pump unless necessary I checked all the wheel speed sensors just in case the codes were wrong. No problems found with the sensors.
I then elected to try changing the ABS control module (5WK8 405) as they're cheap and commonly available on Ebay. So I've tried 2 different ones and both give the same errors.
I then bought a used (but supposedly tested and working) pump - it's the yellow label one for my car so a bit pricey but still a lot cheaper than a "new" one (no longer available on some BMW databases). I plugged it in, without connecting it to the actual brake lines, just to see whether the codes changed. They didn't!
I've since tried all sorts of combinations, disconnecting wheel sensors etc... and even disconnecting the battery between each change just in case the ECU is "remembering" the codes but nothing changes the codes.
So, I've come to the conclusion that either all 3 ABS controllers are faulty or there's a wiring fault.
I'm not sure what to try next. I've printed off the pin-out for the ABS controller connector - thank you to whoever put it on the resource pages, so I'm going to attempt to check the wiring.
I'm also tempted to open up one of the control modules too.
Am I missing something (apart from a few marbles - as I feel this is frying my brain)?
Thanks for taking the time to read this. Any pointers would be appreciated.
Richard
