Originally Posted by 850man

I just wanted to let everyone know that I finally figured out what was wrong with my 850’s speedometer (working sometimes and not working other times). A very smart Volvo mechanic finally told me it was the ABS unit. I thought he was pulling my leg, but I contacted WWW.AUTOECU.COM, and they verified that the ABS unit would definitely cause the speedometer to work erratically (speedometer sensor wiring runs through the ABS module). I removed the electronics portion of the ABS (also found out you can take this part off and drive fine – no brake fluid loss or anything – brakes still work, just no ABS – until it’s reinstalled) and sent it to WWW.AUTOECU.COM. They rebuilt the module, updated it, and fixed any potential problems. They were great. I had it back in a few days, and it fixed the problem just like they said it would. BTW – the electronics part of the ABS isn’t so bad to take off, but you do need a small reverse Torx socket to take out the 4 screw/bolts. The wiring just unplugs. If the screws were easier to get to it would be super easy. I did have to remove the air filter to get to these 4 module mounting screws. Anyway, just wanted to let anyone know that’s having erratic speedometer problems, it could be your ABS – especially on a 1997 Volvo 850. I searched for months, replaced parts, and couldn’t find any info on it anywhere on-line – certainly not this solution. Just thought someone should share the info!

Originally Posted by 850man

I have a 1997 850 GLT. The speedometer works erratically. Occasionally it works just fine, but most of the time – nothing. The odometer stops when the speedometer stops. I tried replacing the speedometer, and the sensor on the transmission. Neither changed its erratic ways. I also tried unplugging and plugging the connectors under the dash, below the fuse block. I even tried jacking it up, putting in gear and watching the speedometer while I moved and shook wires. Nothing made a difference. Any ideas? Where could I get a schematic or drawing to show me exactly how the wiring runs from the sensor to the speedometer? I may need to trace out every inch of wiring. Any help would be appreciated.