Test 34A - Antilock Warning Lamp Circuit (Code 89)

Test 34A: Repairing Code (89) Antilock Warning Lamp Circuit:

NOTE: When connecting or disconnecting connectors and inspecting connectors clean and repair as necessary.

NOTE: After completion of a repair or test then perform Verification Test. Verification Test VER-1A - ABS

NAME OF CODE:
Antilock Warning Lamp Circuit

SET CONDITION:
The following criteria must be met for this code to be detected.
1. Microprocessor control software not generating pulses for the external watchdog.
2. High feedback voltage from the low side of the ANTILOCK warning lamp.
3. Criteria 1 and 2 satisfied for 30 consecutive checks spaced 5 ms apart.

THEORY OF OPERATION:
Whenever the Controller Antilock Brake (CAB's) external watchdog circuit is not functioning, the ABS main relay should be de-energized and the pump motor feedback voltage should be low. If it is not and the problem persists long enough to rule out noise in the pump/motor feedback and to account for response delay in the external watchdog circuit, the (89) Antilock Warning Lamp Circuit Failure code is set.

POSSIBLE CAUSES:
- Anything that keeps ANTILOCK warning lamp feedback voltage high when the yellow ANTILOCK warning lamp is supposed to be turned on
- Shorted to vehicle battery voltage in the wiring between ANTILOCK
- warning lamp and the CAB
- 0pen ABS warning lamp driver circuit to relay
- Normally closed ABS warning lamp relay contacts Open
- 0pen ABS warning lamp relay ground circuit
- 0pen ABS warning lamp relay driver transistor in the CAB
- Short to high voltage in the lamp feedback path within the CAB

Power Distribution Center: