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RWAL Diagnostics
As we said earlier, the self-diagnostic capability of the Kelsey-Hayes RABS and RWAL systems are limited and can store only one fault code at a time. When a fault is detected, the amber ABS warning light on Ford and Dodge applications, or the red brake light on GM applications, will come on and the ABS function will be disabled. The red brake warning light may also come on if a hydraulic failure occurs in the brake system, or the parking brake has been set.
In GM applications, the brake warning light will be brightest when grounded by the parking brake, a little dimmer when grounded by the hydraulic system and dimmest when grounded by the ABS controller.
To determine the cause of a red brake warning light in a GM application:
Set the parking brake. If the light gets brighter, the problem is not the parking brake.
Unplug the connector from the combination valve by the master cylinder. If the light remains on, the fault is in the ABS system and further diagnosis is required.
ABS Fault Code Access
On GM vehicles, fault codes can be retrieved manually (flash codes) by jumping terminals "A" and "H" (or grounding terminal "H") on the diagnostic connector, or you can use a scan tool such as a Tech 1 or Tech 2. On Ford and Dodge trucks, fault codes can be accessed manually by grounding the diagnostic pigtail connector on the ABS control module.
The flash code sequence for Ford, GM, Dodge and import trucks with the Kelsey-Hayes rear-wheel ABS system are the same, but the flash codes are slightly different. If you're reading flash codes, start counting from the first long flash. Then add the short flashes that follow. The total of the long flash plus any short flashes that follow equals the number of the code.
Because the system can only do one code at a time, the first code must be read out, diagnosed and repaired before the system can generate any additional codes.
Beginning in August 1990, a software change was made in the ABS controller on all General Motors RWAL equipped vehicles. The change transforms codes 6, 9 and 10 into "soft" (non-latching) codes that only illuminate the warming light as long as the fault is present. If the fault is intermittent and no longer exists, the light will go out with the next ignition cycle. The conditions under which the codes are set remains the same, as do the basic diagnostic procedures.
A scan tool must be used on the newer GM applications to read any soft (non-latching) codes that might be present because grounding the "H" terminal on the ALDL connector erases soft codes.
RWAL Fault codes
Codes for Dodge RWAL, Ford RABS and GM RWAL applications are similar but have a few differences:
- Should not occur (replace the controller if it does)
- Open isolation valve circuit or defective ABS module
- Open dump valve circuit or defective ABS module
- Grounded or closed RABS or RWAL valve switch
- Excessive actuations of dump valve during ABS braking
- Erratic speed sensor signal
- Shorted isolation valve or defective ABS module
- Shorter dump valve or defective ABS module
- High resistance or open speed sensor circuit (resistance should be 1000 to 2500 ohms)
- Low speed sensor resistance (Dodge & Ford only)
- Open speed sensor circuit (GM only)
- Stop lamp switch circuit (Dodge & Ford)
- ABS module speed processor (Dodge & Ford only)
- ABS module program (Dodge & Ford only)
- ABS module RAM memory failure (Dodge & Ford)
To manually clear a stored fault code on GM and some Dodge trucks with RWAL, remove the ABS fuse or disconnect the battery for 5 seconds. Ford RABS codes will automatically clear when the ignition is turned to the off position.
False codes
Kelsey-Hayes RWAL and RABS systems are vulnerable to a number of false codes. If terminal "H" on the ALDL connector is grounded when the warning light is not on, it will set a code 9. Nothing is really wrong with the system and the code can be cleared.
On 1989-90 GM "S" and "T" series trucks, and 1988-90 "C" and "K" series trucks with manual transmissions, a false code 7 can be set if the blower motor is set on high, and the ignition is turned off while the brakes are applied and the truck is still moving. This "glitch" was eliminated on 1991 models when a change was made in the ABS module.
Another false code problem has been noted on some 1988 and '89 "C" and "K" series GM trucks. A code 10 may be set when the vehicle is traveling over 37 miles-per-hour and the ABS controller sees an open circuit or no voltage in the stop lamp switch circuit. Later models have a revised brake pedal switch that eliminates the problem.
