1995 850: Need help diagnosing ABS fault codes

[beckettloose]

Hello all,

I have a 1995 Volvo 850 Turbo Wagon (with TRACS) that has a persistent ABS warning, TRACS warning, and flashing service light. After clearing all the codes, the following re-appeared after a test drive:

4-2-3 TRACS Valve Circuit Open/Short
4-4-4 No Power Supply to Hydraulic Unit Valves

I already tried replacing the ABS combination relay with the one from my parts car, but it did not solve the issue. Would the next logical step be to swap the entire 'hydraulic modulator'? Unfortunately the engine and transmission are currently out of the car while I prepare everything for a manual swap, so I won't be able to test any fixes for a while. However, any advice would be greatly appreciated.

Thanks,
Beckett

[scot850]

That might point towards the power connector connections in the ABS unit have broken. Not an uncommon issue at this age. Once you get the car back up and running, try wedging some cardboard between the cable connector and the ABS module and see if this error goes away. If it does the ABS module needs resoldering. As always we suggest contacting Matt and Mid-West ABS. Check his website for trouble shooting.

Neil.

[jreed]

Agreed with above, and in addition I recommend checking the insulation on the wires leading to the ABS. At least on my 97 855, this cracks/crumbles and shorts against the metal body. I applied split loom insulation over the wires to fix.

[Vova585]

Those codes suggest circut issue.
I would obtain diagram for the unit(all data or vida). Carefully check all powers and grounds to the ABS module. I would use 2amp test light(any 24watt bulb laying) to make sure you are "loading" circut. If all powers and grounds are good-retest each of them but this time while doing "wiggle test" of the wiring harness close to the connector. Be careful with frontprobing-use proper small needle connectors. With backprobing use small t-pins. Good luck