ABS unsolved mystery
 

Hello everybody. ABS problem on 850's are well known, as a volvo owner I have the same common problem with my ABS system. Let me give you some info about what I did on my 1996 850 during last couple of months this may help you to give me some advise to solve this nerve damaging cituation. ABS module replaced twice, wheel sensors checked with scope was fine, cleaned and reinstalled twice and last time I replaced the front sensors with new ones comlete brake job rotors and pads, ignition switch, and all possible vissual inspection but no luck still my ABS light comes on mostly when I'm driving on a stop and go situation and I need to stop the car turn the ignition off and start again drive for some distance and light goes off untill next time, I;m going to check brake pedal switch today and clean the abs connector with some WD40 to see if might help. My Q. is there any procidure to reset the ABS module? do I need to do that and how? Thanks all for your help and time.

I am thinking the brake pedal switch just because it is the only thing left to check. I have to ask, through all of this, did you check the codes in the ABS computer? It should tell you what the issue is.

Thank you for your respond, I have to say no I did not check the abs for any code stored because my obd code scaner don't work for that and the car is 1996 with obd scaner socket inside and no code reader ability like the 1995 and older in the engine compartment so I was able to check my wheel sensors by my osciloscope and find all four sensors ok with identical output waves I will chek asap to see my last resort, the pedal switch. is it possible to read the abs codes without dealers help by some diy procidure? and if possible how? Thanks again.
Art.

ABS unsolved mystery
 

[quote=fcpgroton;230453]I am thinking the brake pedal switch just because it is the only thing left to check. I have to ask, through all of this, did you check the codes in the ABS computer? It should tell you what the issue is.[/quote

Today I was able to remove the brake pedal switch and replace but before finish the job I was concern about the switch working condition and that was it, the switch was damaged when I checked with multimeter, so I'm really happy because finaly I found something wrong in the system, still worry but I'm sure that was my reall problem since started and took a long time and hard work to finish. By the way to make sure everything is OK I have to drive for couple of days and will post new finding if any. hope not. Thanks again'
Art.

I had my ABS system diagnosed and the Volvo tech found the brake light wiring to the trunk mounted spoiler was causing issues as with the brake pedal switch. After disconnecting the spoiler wiring and replacing the brake pedal switch with a brand new one, the ABS light stayed off for a while (maybe three weeks) then yesterday it came back on while braking over a speed bump. Im wondering if this could be due to the two connections on the brake pedal switch being plugged in backwards? I could not tell on the brake pedal switch if it mattered which side I plugged up to..