Greetings

On the morning commute today my brake failure light came on. Curious, brakes work as normal, brake fluid level is up, unchanged. I turned the engine off, started it again and light is on again. I'm assuming a wiring fault.

Any ideas?

1981 245 B21F K-Jet, M46

Thanks
Scott

Car not moving and not needing brakes to hold in place (not on a hill) and with engine running.

Step hard on brakes. Any change in warning light?

Step very lightly on brakes. Does the pedal sort of give way and allow you to push it slowly to floorward? If YES - the master cylinder is failing.

Light pedal pressure does not flare the piston seals strongly against the cylinder walls. Failing seals will then allow brake fluid to pass around the seal edges, and thus the pedal moves on down.

If one seal is failing worse that the other, that could create pressures in one circuit lower than in the other - and that would trigger the warning light.

Test and post back as another post in this thread.

Good Luck,

Bob

:>)

Firing up the car the light stays on. Push hard on the brake pedal, no change in status of light. Pedal is firm. Slowly push on brake pedal, pedal is firm at about 6 inches or so from floor, and when I release pedal, the light flicks off o so briefly then is on again. Just at the point of release from bottom of pedal stroke the light flicks off quickly then back on again, and only when pushed down gently.

I've had master cylinders fail on other cars before, so I know what that is all about, but I've not had a Volvo before, so I appreciate all the help I get here.

Thanks

Scott

The brake failure light detects an imbalance in the hydrolic fluid. DO NOT ASSUME A WIRING PROBLEM AS IT MAY BE SOMETHING ELSE! When the master cylinder starts to fail usually one seal fails before the other the system detects the imbalance in pressure and the warning light goes off. It's kind of hard to know if there is something wrong from the way the car brakes and even the pedal feel will be about the same. That's because it's a double default system that still brakes safely with half the system down, basically all that happens at first is that you lose the brakes on one rear wheel, which is pretty hard to tell.

Thanks Patrick

I was trying to feel a difference in pedal pressure but it's tough.

Tomorrow I'll do some detailed troubleshooting.

Thanks again

Scott