Apologies if this resolution has been posted before.
I recently had a safety inspection performed on a new-to-me 96 C4S. After the inspection the ABS/ABD lights began to come on intermittently and I called the shop to ask if anything had been unplugged in testing the braking system and they said that the only testing involved scanning the ECU. Initially, the lights came on randomly and then came on virtually all the time. I have a Durametric scanner and found the fault was localized to the LF sensor. Since I suspected that something had been messed with during the inspection I tried removing and reconnecting the sensor connector and the warning lights went away - but did come back on after a short period. I then just jiggled the wire near to the connector and got the warning lights to go out. I purchased a new sensor, installed it and the issue is now resolved. I have tested the old sensor for continuity by moving the cable at the connector and jiggling it will cause a break in the connection. It may just be the age of the car but clearly the wiring at the connector end of the cable can be the source of ABS/ABD warning lamp issues.
Also, there is a TSB warning to replace wheel speed sensors in pairs for cars produced before late Nov/95.
Last edited by brendanm; 06-24-2017 at 08:44 AM.