Test Description
Anti-Lock Warning Lamp
The amber Anti-lock warning lamp is located in the instrument panel cluster. This lamp will illuminate when the EBCM detects a malfunction in the anti-lock brake system. The warning lamp is intended only to warn the driver that a condition has been detected which results in partial or total reduction of the anti-lock brake system. Under this condition full operation of the standard hydraulic braking system is available. If both the red Brake and the amber Anti-Lock brake lights are illuminated, there may be something wrong with the hydraulic brake system, limiting all braking functions.
ABS System Self-Diagnosis Description
In the process of controlling the anti-lock brake system, the Electronic Brake Control Module (EBCM) continually monitors operating conditions for possible malfunctions. By comparing system conditions against standard operating limits, certain circuit and component malfunctions can be detected. A four-digit numerical trouble code is stored in computer memory when a problem is detected by this self-diagnostic system. The trouble codes can later be accessed with a bi-directional scan tool.
To access trouble codes, connect a bi-directional scan tool to the Assembly Line Diagnostic Link (ALDL) connector, then follow manufacturer's instruction for use of the tool. After code have been read, proceed to DIAGNOSTIC CHARTS/ABS CODE DIAGNOSIS GUIDE, if the ABS Functional Test has been performed. After repairs have been made, clear all codes, using the scan tool.
History & Current ABS Codes
The ABS trouble codes which may be stored by the EBCM are not specifically designated as Current or History codes. The Anti-lock lamp may be used to differentiate between Current and History codes.
If the Anti-lock lamp is illuminated prior to entering the ABS diagnostic mode, at least one of the stored codes is current. If the Anti-lock lamp is not illuminated prior to entering the ABS diagnostic mode, none of the stored codes are current.
If more than one code is stored and the Anti-lock lamp was illuminated prior to entering the diagnostic mode, it is impossible to determine which code is Current or History.
Note On Intermittents
Intermittent failures in the anti-lock brake system may be difficult to accurately diagnose. The ABS trouble codes which may be stored by the EBCM are not designated as Current or History codes. These codes can be helpful in diagnosing intermittent conditions.
If an intermittent condition is being diagnosed, the ABS system can be used in the following manner to help isolate the suspected circuit.
1. Display, then clear any ABS trouble codes present in the EBCM.
2. Test Drive Vehicle, attempting to repeat failure condition. A description of driving conditions under which the last failure occurred can be helpful.
3. After duplicating condition, stop the vehicle, then display any trouble codes stored.
4. If no codes were stored, proceed to DIAGNOSTIC CHARTS/SYMPTOM DIAGNOSIS GUIDE.
5. If a code was stored, check electrical connections and wiring for the following:
a. Poor mating of connector halves.
b. Terminals not fully seated in connector halves.
c. Improperly formed, or damaged terminals. All connector terminals in a problem circuit should be carefully reformed to increase contact tension.
d. Poor terminal to wire connection. In most cases, this will require removing wire from connector body.
6. If a complaint of intermittent warning lamp operation is encountered, the following circuits to the EBCM should be checked:
a. Low system voltage. If low voltage is detected at the EBCM, the Anti-lock lamp will illuminate until normal operating voltage is detected.
b. Low brake fluid. This condition in the Pressure Modulator Valve (PMV) reservoir will cause the Brake and Anti-lock lamps to illuminate. When an acceptable fluid level is registered, the lamps will no longer be illuminated.
7. Any condition which results in interruption of power to the EBCM or hydraulic unit may cause the warning lamps to turn on intermittently. These circuits include the main relay, pump motor relay, fuses and related wiring.