850 ABS

[mdwalker86]

I really need some help here. Even my favorite Volvo dealership mechanic is stumped by this one. I have a 1993 850 GLT Sedan, non-turbo automatic. The rear brakes quit working altogether. Both calipers are fine, but no fluid is getting back there. Even a pressure bleed did not get any fluid back there. During a DIY session at my local dealership, I found that only the right front brake works. Immediately I questioned the ABS but no major codes returned. Here are the codes I got:

A3– ABS

142 Faulty brake pedal switch, open or short
213 Left rear wheel sensor, no signal on moving off
214 Right rear wheel sensor, no signal on moving off

The mechanic did not want to write-off the ABS unit and oddly enough, it seems to function on my last remaining wheel (right front passenger) that still has any brake action at all.

So, meanwhile I use the emergency brake to get a little traction from the rear and rely on the right front wheel to do the rest.

Any thoughts before I spring for a new/rebuilt/junkyard ABS unit?

[Ozark Lee]

The brake lines do route through the modulator on the ABS system but I have not encountered one before that totally blocked the brake lines. That said, it certainly is possible.

I think I would start by loosening the lines that go into the modulator and see if you have brake fluid pressure there. If you don't have pressure then it would point to a problem with the master cylinder. If you do have pressure going into the modulator then check the brake lines that go out of the modulator to the calipers. If you don't have pressure there but do have pressure coming in then the modulator is shot.

The good news is that the ABS system on the older 850s (pre '96) rarely fail and, as such, they are cheap on eBay or junk yards. Make sure the numbers match if you do replace the system.

...Lee