Removal & Installation
- Remove any instrument panel covers to gain access to the module.
- Disconnect the wiring harness to the module.
- Remove the retaining screws and remove the module.
- Place the module in position against the under dash crossmember. Install and tighten the retaining bolts.
- Connect the wiring harness to the module.
- Install any instrument panels which were removed.
- Check the system for proper operation.
Diagnosis & Testing
System Self Test
The RABS module performs system tests and self-tests during startup and normal operation. The valve, sensor and fluid level circuits are monitored for proper operation. If a fault is found, the RABS will be deactivated and the ABS light will be lit until the ignition is turned OFF. When the light is lit, the diagnostic flashout code may be obtained. Under normal operation, the light will stay on for about 2 seconds while the ignition switch is in the ON position and will go out shortly after. A flash code may be obtained only when the light is ON. Before reading the code, drive the vehicle to a level area and place the shift lever in the PARK or NEUTRAL position. Keep the vehicle ignition ON.
All vehicles use the RABS II system. The major difference between the two systems is the addition of keep alive memory (codes are stored, even if ignition is turned off), and a code 16 can be set which means the system is operating properly.
In the case of more than one malfunction, only the first trouble code will appear. The next code will appear only after the first one has been corrected.
TO OBTAIN THE FLASH CODE:
Locate the RABS diagnostic connector and attach a jumper wire to it and momentarily (1 to 2 seconds) ground it to the chassis. The RABS diagnostic connector can be found in the following locations:
1994 B Series Pick-up: under the instrument panel on the driver's side (Black connector-Black/Orange wire)
- Quickly remove the ground. When the ground is made and then removed, the RABS light will begin to flash.
- The code consists of a number of short flashes and ends with a long flash. Count the short flashes and include the following long flash in the count to obtain the code number. Example 3 short flashes and one long flash indicated Code No. 4. The code will continue until the ignition is turned OFF . Refer to the flashcode diagnosis charts for further instructions.
To clear the codes, perform the following steps:
- Unplug the test connector.
- Turn the ignition switch to the OFF position.
- Plug in the test connector.
The ring is located on the differential case inside the axle housing. Once it is pressed off the case it cannot be reused. This job should be left to a qualified service technician as it requires the rear differential to be disassembled.
The rear wheel anti-lock system continually monitors rear wheel speed with a sensor mounted on the rear axle. When the teeth on an excitor ring, mounted on the differential ring gear, pass the sensor pole piece, an AC voltage is induced in the sensor circuit with a frequency proportional to the average rear wheel speed. In the event of an impending lockup condition during braking, the anti-lock system modulates hydraulic pressure to the rear brakes inhibiting rear wheel lockup.
When the brake pedal is applied, a control module senses the drop in rear wheel speed. If the rate of deceleration is too great, indicating that wheel lockup is going to occur, the module activates the electro-hydraulic valve causing the isolation valve to close. With the isolation 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 module will energize the dump solenoid with a series of rapid pulses to bleed off rear cylinder fluid into an accumulator built into the electro-hydraulic valve. This will reduce the rear wheel cylinder pressure and allow the rear wheels to spin back to the vehicle speed. Continuing under module control, the dump and isolation solenoids will be pulsed in a manner that will keep the rear wheels rotating while still maintaining high levels of deceleration during braking.
At the end of the stop, when the operator releases the brake pedal, the isolation valve de-energizes and any fluid in the accumulator is returned to the master cylinder. Normal brake operation is resumed.
Removal & Installation
Hydraulic Control Unit
- Disconnect the brake lines from the valve and plug the lines.
- Disconnect the wiring harness at the valve.
- Remove the 3 nuts retaining the valve to the frame rail and lift out the valve.
- Installation is the reverse of removal. Don't overtighten the brake lines. Bleed the brakes.
Removal & Installation
- Thoroughly clean the axle housing around the sensor.
- Disconnect the electrical harness plug from the sensor.
- Remove the sensor hold-down bolt.
- Remove the sensor by pulling it straight out of the axle housing.
- Ensure that the axle surface is and that no dirt can enter the housing.
- If a new sensor is being installed, lubricate the O-ring with clean engine oil. If the old sensor is being installed, clean it thoroughly and install a new O-ring coated with clean engine oil. Carefully push the sensor into the housing aligning the mounting flange hole with the threaded hole in the housing.
- Tighten the hold-down bolt to 25-30 ft. lbs. (34-40 Nm) for the B Series Pick-up and 12-16 ft. lbs. (16-22 Nm) for the MPV.
- Remove the RABS sensor from the axle housing.
- Connect a Digital Volt/Ohm Meter (DVOM) across the two sensor terminals and record the reading.
- The reading should be between 0.9 and 2.5k Ohms.
- If not, replace the sensor.