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Apologies in advance for the long post.
I plowed through hundreds of ABS/Tracs light issues in the archives but did not locate any information on what to look for next when a replacement ABS module did not do the trick of extinguishing the ABS/Trac lights on the dash of my wife's '96 850 Turbo Wagon, 120K.
My wife's '96 850 has had isolated ABS/Tracs light on issues since I purchased it two and a half years ago. Typically the lights would come on during a long, hard, summer run, then go off with the next restart, perhaps twice in the first year, increasing somewhat in the second year, but still rare and always going off after a restart. In winter the ABS and Traction performed beautifully. I did not drive the car much last spring or summer so I don't know of the frequency of the lights coming on before catastrophic ABS module failure last summer, in 100 degree heat, at which time we lost the speedometer too.
After researching the issue on Brickboard, I removed and sent my ABS module to Victor Roca (Vitor on Brickboard) in California. The lower 1/4th of my internal ABS board, however, was seriously fried beyond repair (I can send a jpeg image if anyone is interested), so I had to wait a few weeks for Victor get a rebuildable one and send it to me.
When the lights stayed on during the first test drive I discovered the fuse I had removed as per instructions was blown. With subsequence test drives, however, the lights would go off after starting but come back on after it reached 15 mph or so when the ABS unit checks all the solenoids, etc. I did about 6 or so test drives around the block to determine if was indeed speed related (not engine rpm, etc) and then pulled the wires to the pump (but not to the ABS module, so all the speedometer/trip functions are now as they were before) and have been driving it with the pump wires disconnected for three months since.
In subsequent correspondence with Victor, he suggested that the fried area of the board indicated that it a frozen pump or shorted wires to the pump had blasted the ABS module. I lined up a used ABS pump in Florida but thought I had better check mine first, as someone on the Brickboard had said that the pump works under power applied or it does not. I hooked up a 12 V battery source to the pump and it whirred away with each contact. I have not been able to make a comparison test with another vehicle, but I presume the vibrating, high-speed ratcheting sound from the pump is its normal operation. If the operation of the pump is supposed to be nearly silent, with no high-speed pulsation, then I guess perhaps the pump is going. The parts person at Volvo Houston said the only pump failures they have seen are leaking seals. And a mechanic on the Brickboard said he has seen only one pump failure in five years.
So if it's not the module, and it's not the pump, what is next? A friend who has been reading on Brickboard arm-twisted me into ordering the two rear wheel sensors, which arrived today, but it seems like a $110.00 gamble. Why rear and not front? Should I clean all of them first? Part of my problem is that I live (Wyoming) 300 miles from the nearest dealer (Billings, MT or Denver, CO). Would a shop with a generic code reader be able to pull all the appropriate codes to give an idea of where the trouble lies? Or do I need to go to Volvo for that? And will these fault codes show up at idle or does the wagon need to be driven to 18mph to trip the code errors? I have experienced none of the intermittent ABS/Tracs light and other erratic issues associated with ignition switch problems, so I don't think that is the issue. I have read of the pedal-height sensor issue (141 code) and that is a possibility, but it would seem a bizarre coincidence. But the overriding issue still remains: what fried the board on the ABS module (a rare happening, Victor says)? Anyone make an intelligent guess as to what my next step should be?
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