For some time now, I've had an intermittent ABS light on my 91 300D. Significantly, the light would come on while idling in the driveway. So that pointed me in the direction of the ABS module and/or relays. So I swapped those out with used, bench-tested (presumably) units.

What I've found is that, while the intermittency pattern has changed, the light still comes on at times. So while swapping the parts had an effect, it has not eliminated the problem.

Another data point: disconnecting the battery for a period of time seems temporarily to solve the problem.

I went the route that I went because the parts were fairly cheap and easy to replace.

My assumption (perhaps incorrect) is that dirty sensors are unlikely to be the issue since the light will come on with no wheel rotation. But, it terms of what to try next, should I just clean the sensors and see if there's any improvement?

The nuclear option is to change the registration of the car to classic so that the safety inspection will no longer be a state requirement.

__________________
14 E250 Bluetec 4Matic "Sinclair", Palladium Silver on Black, 157k miles
06 E320 CDI "Rutherford", Black on Tan, 175k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver on Tan, 144k mi, wastegate conversion, ALDA delete

19 Honda CR-V EX 70k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife

My 91 TE had the ABS light AND the SRS on, it was a bad voltage regulator.

__________________
"Rudeness is a weak man's imitation of strength" - Eric Hoffer

I'm pretty sure my voltage is good.

__________________
14 E250 Bluetec 4Matic "Sinclair", Palladium Silver on Black, 157k miles
06 E320 CDI "Rutherford", Black on Tan, 175k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver on Tan, 144k mi, wastegate conversion, ALDA delete

19 Honda CR-V EX 70k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife

I had the same issue with my 91. Turned out to be a failing OVP relay.

__________________
RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

99 W210 E300 Turbo Diesel, chipped, DPF/Converter Delete. Still needs EGR Delete, 232K

90 Dodge D250 5.9 Cummins/5 speed. 400K

Gone and still missed...1982 w123 300D, 1991 w124 300D

Does the abs actually work? Have you tried to make it go?

I do believe these Bosch systems can provide codes. Have you looked through the FSM?

Worse comes to worst, pull the bulb? How intermittent is is? Like routinely on and off or seldomly?

__________________
Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (116k)
1991 350SD (206k)
1991 300D (228k)
2008 ML320 CDI (199k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (267k)

Past Diesels:
1983 300D (228K), 1985 300D (233K), 1993 300D 2.5T (338k), 1993 300SD (291k)

Interestingly, a while back I had the ABS light accompanied by rough idle. So I knew that was the OVP relay. Amazingly, among the random odd lot of spare parts I found lying around, I had TWO used OVP relays. So I installed one of those and the rough idle problem went away. However, since it's an old used part, I don't know for certain if it's functioning flawlessly. So I just swapped it out for the other one and we'll see what happens. I'm not opposed to ordering a new one....they're fairly cheap.

__________________
14 E250 Bluetec 4Matic "Sinclair", Palladium Silver on Black, 157k miles
06 E320 CDI "Rutherford", Black on Tan, 175k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver on Tan, 144k mi, wastegate conversion, ALDA delete

19 Honda CR-V EX 70k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife

Not sure...haven't tried. I assume it works if the light is not on.

No ABS codes with my model...looked into that a while back.

I think pulling the bulb might get flagged by an observant inspector.

Literally every time I drive the car the light will come on and usually stay on.

__________________
14 E250 Bluetec 4Matic "Sinclair", Palladium Silver on Black, 157k miles
06 E320 CDI "Rutherford", Black on Tan, 175k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver on Tan, 144k mi, wastegate conversion, ALDA delete

19 Honda CR-V EX 70k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife

Update: just took it for a 30 minute drive and the light did not come on. My mistake in retrospect was assuming that the used OVP relay was good just because it solved the rough idle problem. If the problem emerges again I will buy a new OVP relay.

So now I have an extra ABS module for a rainy day! haha

__________________
14 E250 Bluetec 4Matic "Sinclair", Palladium Silver on Black, 157k miles
06 E320 CDI "Rutherford", Black on Tan, 175k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver on Tan, 144k mi, wastegate conversion, ALDA delete

19 Honda CR-V EX 70k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife