99 Ford Ranger / 4 cyl / Auto / Standard Cab / with RABS

Since I have had this truck there has been an issue with the amber ABS and the red brake light coming illuminating at random times (at least we thought it was random). The system fluid level is correct and the system is not losing any fluid externally. After a lot of effort the problem persists. The work done so far:

1) Changed fluid level switch
2) Changed rear diff sensor
3) Check RABS code (4 flashes)
4) Checked wiring specified in manual for 4 flashes
5) Changed RABS module (junk yard unit)

After all that both lights continue to illuminate, but while trying to figure this out we discover we can make both lights come on by doing the following. With the lights out and the truck stationary press and hold the brake pedal. The pedal is firm for a few seconds, but then it gets a little soft and if you continue to hold pressure on the brake pedal the pedal will drop a little and then both lights come on. It will do this every time it’s tried. When driving the brakes seem to operate fine but I guess we might not notice a small leak down when holding the brakes.

So that seemed like an internal system leak (no external leaks visible – no fluid loss) we changed the brake master cylinder. This made no change to the problem. The garage is stumped and waiting for it’s master mechanic to return from vacation.

My thought is that the only thing left is the ABS valves that modify (dump) the brake pressure when a skid is detected. I believe the assembly is called the proportioning valve switch assembly?

Any thoughts / input appreciated.

 

Posting an update on this issue in case someone else finds the info useful in the future.

The problem turned out to be caused by a faulty ABS valve. We installed one off a truck from the salvage yard ($15) and the problem was gone. Hurray!

The service manual does list this as the next step for 4 flashes error code if the ABS Module does not fix the problem.

 

Good info, thanks for the update. I disabled my abs when I did my 4x4 swap, wish we coulda helped u out