Problem with ABS light
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 itís 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 Ė no fluid loss) we changed the brake master cylinder. This made no change to the problem. The garage is stumped and waiting for itís 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.