Dgohwanger wrote: Aug 15, 2022 1:33 PM
I installed mine this weekend. It looks great! Thanks, cek for the troubleshooting help!
This morning I noticed my anti-lock brake light was on...has anyone had this issue after the retrofit installation? Maybe it's just a bad sensor and timing coincidence...?
Likely a coincidence, but let's dive in and find out...
Using the '85 E28 ETM since you have a 1985 535i:
ABS itself runs directly from the battery (ABS ECU gets its power from the Ignition switch in RUN position, and the ABS Pump gets power directly from the battery). Fuse 12 does go to the brake switch, and when the pedal is pushed, 12V goes to Pin 25 of the ABS ECU.
I cannot find any more info on the ABS Warning Indicator on the diagrams for the instrument cluster. Never noticed this before. I checked the '88 ETM and it's not there either. Odd (maybe I'm not seeing it?).
Anyway, from the above pages, it appears the ABS Indicator light gets 12V from the ignition switch when in "RUN" via the .75 GN wire that also powers the ABS ECU (Pin 1) ("M").
The ABS Indicator light ALSO gets 12V from two other sources:
- Pin 1 from the ABS Hydrauluc unit (.75 GY/RD).
- Pin 29 BK/GY on the ABS ECU) if it detects a bad sensor amongst other things.
I don't think it's possible for that light to come on unless EITHER Pin 29 of the ECU or Pin 1 of the ABS unit is hot.
Further, I don't see any wires in the fuse box itself that deal directly with the ABS system (other than Fuse 12. See xls here:
https://kindel-my.sharepoint.com/:x:/p/ ... i7Jg-h-2kg
Thus I think this is a coincidence and either
- An ABS sensor has failed (a common thing)
- The ABS pump has failed (uncommon IIRC)
- The ABS ECU has failed (uncommon IIRC)
Your best bet now is to read one of the many threads on testing the ABS sensors...