Brake and ABS light on

[bobwalter]

OK, here is the story. I was running a wire from the front to the rear of my Class C. (1992 F-350 chassis) I disturbed the area over the left rear axle. When I went to move the unit back to the side yard the brake and ABS light were lit. I am thinking I knocked a wire loose. Anyone have info of what I should expect to see when I pull the duals off that side? I am thinking there is probably an ABS sensor on the axle??????? (Maybee) I have not had time to pull the wheels yet but I am doing it tomorrow afternoon. Any help would be great.

Thanks,

Bob

[Scooter]

You might not have to pull the wheels off. Perhaps the ABS sensor can be pushed back in (after cleaning).

[subford]

A bad wheel cylinder would be the only thing I can think of to pull the rear wheels. And that is if it is leaking. The only sensor back there is the one in the top of the rear in the center.

The Rear Anti-lock Brake System (RABS) continuously monitors rear wheel speed with a sensor mounted on the rear axle. When the teeth on an excitor ring (mounted on the ring gear) pass the sensor pole piece, an AC voltage with a frequency proportional to the average rear wheel speed is induced in the sensor circuit. In the event of an impending lockup condition during braking, the RABS modulates hydraulic pressure to the rear brakes. This inhibits rear wheel lockup.

When the brake pedal is applied, the Module senses the drop in rear wheel speed. If the rate of deceleration is too great, indicating an impending wheel lockup, the RABS Module activates the electro-hydraulic valve, causing the isolation valve to close. With the isolation valve closed, the rear wheel cylinders are isolated from the master cylinder and the rear brake pressure cannot increase. If the rate of deceleration is still too great, the RABS Module will energize the dump solenoid with a series of rapid pulses to bleed off rear wheel cylinder fluid into an accumulator built into the RABS valve. This will reduce the rear wheel cylinder pressure and allow the rear wheels to spin back up to vehicle speed. Continuing under RABS Module control, the dump and isolation solenoids will be pulsed to keep the rear wheels rotating while maintaining high levels of deceleration during braking.

At the end of the stop, when the operator releases the brake pedal, the isolation valve deenergizes and any fluid in the accumulator is returned to the master cylinder. Normal brake operation is resumed.

System Self-Test
The RABS has self-test capabilities much like those in other electronic control systems. Two warning lamps are located in the instrument panel to alert the driver to a system malfunction. The red BRAKE warning lamp indicates a low fluid level condition or parking brake ON.

The yellow ANTI-LOCK Indicator lights up for approximately 2 seconds when the Ignition Switch is initially moved to ON or START for circuit prove-out. The indicator also lights when the RABS Module detects a malfunction in the system.

The self-test feature contains thirteen codes to indicate the area of the malfunction. When a malfunction is detected, the control module will shut down the system and the yellow REAR ANTI-LOCK Indicator warning lamp will come on to permit normal braking. A code will be set in the system memory that can be retrieved by momentarily grounding the diagnostic pigtail and counting the flashes of the yellow light. If the key is turned off before the diagnostic test is performed, the code will be lost. The light will remain out until another malfunction is detected. If more than one fault exists, only the first code recorded will be displayed. Additional codes will output only after the first fault is corrected.

NOTE :A RABS malfunction will also cause the E4OD Transmission to malfunction.

IF YELLOW REAR ABS LIGHT IS ON AND RED BRAKE LIGHT IS ON THEN CHECK THESE:
1. LOW BRAKE FLUID
2. MASTER CYLINDER FLOAT
3. DIODE/RESISTOR ELEMENT PARKING BRAKE
4. ANTI-LOCK VALVE SWITCH
5. MASTER CYLINDER SWITCH
6. BRAKE LIGHT WIRING

[BFlinn181]

I don't see the need to start with pulling the duals. Check underneath for loose connectors or dislodged sensor for ABS system first.

[subford]

Originally Posted by subford

The only sensor back there is the one in the top of the rear in the center.

SORRY I left out the word "END."

It should have read:
The only sensor back there is the one in the top of the rear END in the center.

Here is an image.

[bobwalter]

Sorry I haven't gotten back sooner. The brake fluid was low. Glad I didn't pull the wheels first. Just shows: Look at the simple solution first. Thanks for the advice, all. Now to monitor it to see if it is losing brake fluid.

Thanks again,

Bob