Just to share with fellow bricksters. What started out as my Tracs and ABS lamps coming on for the first time in 11years, I got a code for "421" "rear inlet valve circuit, open/short circuit". After much troubleshooting by my mechanic and talking to other Volvo techs, all agreed that the Hydraulic Pump is faulty. This is the box that sits under the ABS module and has a number of solenoid operated valves that open and close electrically, hence providing you with the pumping action of ABS. If you have TRACS (I do) then their are extra valves. What's crazy is that this part is not known to fail, but the ABS module usually is the culprit. Anyway, it turns out that the pump is one of the most expensive parts on the car. I was quoted by two different Volvo parts departments, $2,200 Cdn or approx $1,500 American for just the part!!!!
You then have to add 4-6 hrs labour which includes a major bleeding of the system. Of course your "regular" brakes work, you just don't have ABS or TRACS.
I'm not sure what we will miss the most, ABS or TRACS, but I'm guessing I'll miss the TRACS function in the winter most. Needless to say, this $3,000 repair is not going to be done, given the age and mileage of the car. It has just brought my wife and I one step closer to purchasing a brand new S60 T-5 and keep the 850 as our "beater". Yes I will still purchase another Volvo, just hope that if you drive an 850, your Hydraulic Pump never fails....!
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'82 240DL Stock / Masters Class, '94 850 GLT Fully Loaded / Daily Driver, CVC / VCOA Member http://www.capcan.com/tonyg.htm