94 Ranger, 4.0L, Standard Cab / Standard Bed, 5 speed, 214,000 miles.

ABS light stays on all the time, BRAKE light comes on once brakes are applied for first time and also stays on for remainder of time till truck is turned off.

Had to take the bed off to put new fuel pump on, so I went ahead and replaced the ABS sensor that goes into the rear diff while I was already there, hoping that would maybe fix the abs issue, but it did not.

Just wondering what to try next. How many more abs sensors are there on the truck and which of them should I try replacing next?

Thanks.

 

Seeing as how the Brake Warning light is also coming & staying on, check the brake master cylinder fluid level, kinda sounds like it may be low.
If the pads or shoes are worn, the fluid level in the brake master cyl reservoir will drop as they wear, of course if you have a system leak it'll drop, so pull the hood & have a look at the fluid level. If thats ok, thump the reservoir to see if it may be a sticking float, or acting out electrical connection to it.

If you have 4 wheel ABS, check the front wheels ABS sensors, wiring & rotor sensor reluctor vanes for debris, or metal fluff that might be corrupting the front ABS sensors output.

Some thoughts for your suspect list, let us know what you find.

 

Are there any actual sensors on the front wheels? If so, where? Can't seem to find them anywhere. Replaced the one on the rear diff but ABS light still stays on and fronts will definitely lock up whereas they wouldn't before.

 

i could be wrong, but i think a '94 has only rear abs, i know my '93 is that way.

 

You have rear abs (RABS). I just went through a similar problem with my '91 Ranger, the same waring indications. Turned out the problem was the ABS Hydralic unit whic is the pump that produces the pulsing of the rear brakes. I found the unit at O'Reilly's for a much lower price than Ford. Installed it, bled the brakes, the light are out and all is fine.

A auto parts store should be able to read the ABS trouble codes sine both the ABS and the Brake warning lights are lit. Use them as your guide.

Let us know how you make out.

 

First of all, the Ford Ranger RABS system does not have a pump. It has a valve module which has 2 valves in it to perform the following functions:
1. Block the hydraulic line from the master cylinder to the rear brakes to limit pressure in the event of an impending lockup.
2. A dump valve that bleeds pressure off if the wheels have locked up.
It is the cycling of these two valves that you feel as pulsing in the brake pedal.

71FoMoCo, if you can pull the ABS trouble codes I can help diagnose the problem. Pull the codes by folling the instructions here:
Ford Ranger RABS Light And DTCs

Also, do the checks they list there. Does the red brake light illuminate when the key is in the start position? If not, it might be a problem with the 3 wire connection at the master cylinder.

A few other things I've learned about this system.

1. The red brake light illuminates for the following reasons only.
a. key in start to test the lamp circuit and bulb.
b. parking brake depressed.
c. low brake fluid.
It does NOT illuminate for a failed brake hydraulic circuit as it did/does on other cars you might be familiar with.

2. These vehicles do not have a 'proportioning valve' or 'combination valve' as Ford calls it. And the function is not built into the master cylinder. The RABS valve provides the function of proportioning the pressure to the rear brakes.

3. The RABS system is actually a simple system. There's just not enough information/experience out there for most people to feel comfortable with it.

4. The system likes to be CLEAN. Flush/exchange the brake fluid at least every 2 years or when it turns dark. When you flush it out, moisture/dirt is expelled which can corrode the components of the system and lead to a failure.