My friends 91 F150 XLT Larait has had the RABS light on for awhile now. We found what looks to be a vaccuum tube and reconected it to the axle and it made the light go off for awhile. But it came back on. Mine doesnt even have the fitting on the axle to hook up the (vaccuum?) line and the RABS light isnt on. The chiltons book said this is an axle breather valve...what is that? and what could be causing that light? Will we need to pull codes?

 

Here's some info from my 96...dunno if it helps or not

RABS Valve

The rear anti-lock brake system (RABS) valve contains an accumulator, dump solenoid and isolation valve. When activated, the components of the RABS valve work together to control pressure to the rear wheel cylinder (2261), inhibiting rear wheel lockup.

here's a link to the rabs thing:


http://www.motorcraftservice.com/pub...1/STJ69A23.HTM

 

There is a way to determine what is wrong in general by the combinations of the RABS light and the BRAKE light illumination.

In addition, there is a test where the RABS light will flash a code to get more specific faults (I think there are about 16). However, my Chilton's book tells everything about the codes, but nothing on how to trigger the test.

Likely suspects are an inadequate fluid level in the master cylinder, a faulty level measurement of the master cylinder fluid level, or a failed sensor or differential ring in the rear axle.

Could be things like the RABS computer (different from the engine control computer), or the RABS actuator.

The sensor is the only thing on the differential that has wires to it. If you pull this out - can see the toothed ring that it senses. With the axle in the air, you can roll the tires and watch that this ring has a nice even rotation that the sensor can pick up. Missing teeth, etc., are not good.

The RABS control valve is mounted on the driver side frame rail, about under where the driver puts his feet. Don't hear of a lot of problems with this.

Without determining what the RABS computer is telling you, kind of shooting in the dark. But you can try stuff in reverse order of cost.

The vacuum tube you saw was a breather line for the axle - important to keep the outlet up high so that water won't get introduced into the axle via creek-wading or puddle splashing.

 

hmmm that water-axle thing probably has already happened we mudd ALOT sooo yeah probably already did! Thanks ill pass the info on and well go from there

 

now this is probably goin to sound rather weird but does the speedometer still work....i had this same problem in my 92 4x4 and after replacing the rabs and speed sensor in the rear diff (aprox. $20) i got to lookin underneath the truck and found that one of my wires goin to the plug had been cut (dont have a clue how but it was missing a nice little chunk) i simply reconnected the wire and the light went out and the speedo started working again. i located this wire where it splits off the main harness above the rear diff right in front of the rear tank

 

His is a 91 they don't have the electronic speedo/odo.

 

ours arent electric no...but thanks anyways still havent found the problem