ABS light
Lead Driver
Joined: Nov 2002
Posts: 9,557
Likes: 44
From: Concord, NC
The ABS system will do a self test, but it is not the same test as the engine computer. I don't know for sure on a 94, but on my 87 there is a black wire with an orange tracer down near the parking brake pedal with an open connector on the end. If you momentarily ground that wire while the ABS light is lit, it should signal the ABS computer to blink codes on the ABS light. I don't know code definitions or if the wire is in the same place on your truck as mine, but I know that it is possible to get codes one way or another.
Mountain Pass
Joined: Feb 2007
Posts: 121
Likes: 0
From: Central Georgia
Click here to do the self-test for the ABS: http://www1.autozone.com/az/cds/en_u...rInfoPages.htm
If the MC is full and the pedal is firm, I'd bet you've got a bad sensor. I've personally known 5 F-150s in this body era and everyone needed a new RABS sensor in their lifetime. I just replaced mine last week. It's cheap and easy to fix. $15 for the sensor at Advanced and 5 minutes by the rear differential and you're done. See here for how to do it: http://www1.autozone.com/az/cds/en_u...rInfoPages.htm
If the MC is full and the pedal is firm, I'd bet you've got a bad sensor. I've personally known 5 F-150s in this body era and everyone needed a new RABS sensor in their lifetime. I just replaced mine last week. It's cheap and easy to fix. $15 for the sensor at Advanced and 5 minutes by the rear differential and you're done. See here for how to do it: http://www1.autozone.com/az/cds/en_u...rInfoPages.htm
Mountain Pass
Joined: Feb 2007
Posts: 121
Likes: 0
From: Central Georgia
Originally Posted by EPNCSU2006
You mean the wheelspeed sensor on the rear end? It's probably fine if there are not issues with the speedometer....
The RABS sensor is different form the Rear Wheel Speed Sensor found on 4-Wheel ABS vehicles (93-96 Bronocs and F Super Duties).
Senior User
Joined: Dec 2007
Posts: 128
Likes: 0
From: Florida
RABS : Rear Anti-Lock Braking System
There are 2 lights that can come on, the one on the right of the wheel and the other is a dimly lit parking brake light (even if the brake is dis enguaged)
Most of the time it is 1 of 2 components,
1 (the parking Light) will be the rabs pump itself (in the frame, driverside, around the pedals section.) The valve in the pump gets stuck open internally, sorry but they are not servicable and quite expensive unless you find a boneyard with one. Try tapping them with a hammer to disloged the valve , you will need to bleed the system, there is a bleeder valve on the pump also.
The other is the ring gear sensor in the differential ( driver side , on top of the rear chunk.)
Pull it out and wipe it clean, it has a magnetic feild to it and picks up gear particals somtime causing it to malfunction.
If both of these are good , then It could be the RABs computer it self (under the kick pannel above the gas pedal, just to the left of the radio)
Most of the time it is 1 of 2 components,
1 (the parking Light) will be the rabs pump itself (in the frame, driverside, around the pedals section.) The valve in the pump gets stuck open internally, sorry but they are not servicable and quite expensive unless you find a boneyard with one. Try tapping them with a hammer to disloged the valve , you will need to bleed the system, there is a bleeder valve on the pump also.
The other is the ring gear sensor in the differential ( driver side , on top of the rear chunk.)
Pull it out and wipe it clean, it has a magnetic feild to it and picks up gear particals somtime causing it to malfunction.
If both of these are good , then It could be the RABs computer it self (under the kick pannel above the gas pedal, just to the left of the radio)
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Lead Driver
Joined: Nov 2002
Posts: 9,557
Likes: 44
From: Concord, NC
On 92-96 trucks, the same speed sensor feeds the RABS, the PSOM (speedometer/odometer) and the engine computer. The older 87-91 trucks had two separate wheelspeed sensors, one for the RABS, and one for the engine computer in-line with the speedometer cable.
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Mountain Pass
Joined: Feb 2007
Posts: 121
Likes: 0
From: Central Georgia
Originally Posted by EPNCSU2006
On 92-96 trucks, the same speed sensor feeds the RABS, the PSOM (speedometer/odometer) and the engine computer. The older 87-91 trucks had two separate wheelspeed sensors, one for the RABS, and one for the engine computer in-line with the speedometer cable.
Still, the ABS light in my 93 and my brother's 96 were both on as a result of a bad RABS sensor in the rear differential. Neither truck were having any problems with the speedometer. Pulled the sensor in mine just two weeks back and had to replace. No problem whatsoever with the speedo, just the ABS.
If I could just understand what exactly logic was... 
New User
Joined: Mar 2008
Posts: 16
Likes: 0
From: Springfield, MO
When I bought my 92 F250 4x4 the ABS light was on all the time, along with the Parking brake light... I disconnected the battery to work on something else which I assume reset something with the computer.. the ABS light is no longer on, however the parking break light is... Just haven't looked into that yet.
Post Fiend
Joined: Mar 2002
Posts: 19,402
Likes: 38
From: Bonita Springs FL
I doubt any of the RABS sensors actually needed to be replaced. They are so simplistic it's hard for anything to fail. It's just a magnet with two wires coming off it. Sometimes metal filings will collect on the magnet sensor and that will confuse it enough to throw a light. Most of the time the fix is to just wipe it off with a rag.
New User
Joined: Apr 2004
Posts: 18
Likes: 0
From: Charlotte, NC
The ABS system will do a self test, but it is not the same test as the engine computer. I don't know for sure on a 94, but on my 87 there is a black wire with an orange tracer down near the parking brake pedal with an open connector on the end. If you momentarily ground that wire while the ABS light is lit, it should signal the ABS computer to blink codes on the ABS light. I don't know code definitions or if the wire is in the same place on your truck as mine, but I know that it is possible to get codes one way or another.
Lead Driver
Joined: Nov 2002
Posts: 9,557
Likes: 44
From: Concord, NC
Check the wiring connection at the master cylinder. The pins had pushed out of the plastic connector on the wiring harness on my truck. I had an ABS light and could not get codes either, then I found the issue with the master cylinder connector.