General Diagnosis

SELF TEST INFORMATION
The ABX-4 system is equipped with a self diagnostic capability which may be used to assist in isolation of ABS faults. The features of the self diagnostics system are described below.

START-UP CYCLE
The self diagnostic ABS start up cycle begins when the ignition switch is turned to the on position. Electrical checks are completed on ABS components, such as the Controller, decay solenoid continuity, and the system relay operation. During this check the Amber ABS Warning Light is turned on for approximately 5 seconds.

NOTE: If a new Controller Antilock Brake (CAB) is installed on the vehicle, it must be enabled using the DRB. The ABS warning lamp will flash every 1.6 seconds and ABS braking will not be allowed until the CAB is enabled using the DRB.

DRIVE-OFF CYCLE
Further Functional testing is accomplished once the vehicle is set in motion and reaches a speed of about 8kmh (5mph). This cycle is performed only once after each ignition on/off cycle.

^ The solenoid valves and the pump/motor are activated briefly to verify function. If the brake pedal is applied at this time, the test is bypassed.
^ The wheel speed sensor output is verified to be within the correct operating range.

ONGOING TESTS
Other tests are performed on a continuous basis. These include checks for decay solenoid continuity, wheel speed sensor continuity and wheel speed sensor output.

DIAGNOSTIC TROUBLE CODE INFORMATION
Fault codes are kept in the controller's memory until either erased by the technician using the DRB or erased automatically after the vehicle has been driven 35OO miles. Fault codes are retained by the controller even if the ignition is turned off or the battery is disconnected. The only fault that will not be erased automatically is the CAB fault. A CAB fault can only be erased by the technician using the DRB diagnostic tester. More than one fault can be stored at a time. The number of miles the vehicle has been driven since the most recent fault was stored is also displayed. Most functions of the CAB and ABS system can be accessed by the technician for testing and diagnostic purposes by using the DRB.

LATCHING VERSUS NON-LATCHING ABS FAULTS
Some faults detected by the CAB are latching; the fault is latched and ABS braking is disabled until the ignition switch is reset. Thus ABS braking is non operational even if the original fault has disappeared. Other faults are non-latching; any warning lights that are turned on, are only turned on as long as the fault condition exists. As soon as the condition goes away, the ABS Warning Light is turned off, although a fault code will be set in most cases.

INTERMITTENT DIAGNOSTIC TROUBLE CODES
As with virtually any electronic system, intermittent faults in the ABS system may be difficult to accurately diagnose.Most intermittent faults are caused by faulty electrical connections or wiring. When an intermittent fault is encountered, check suspect circuits for:

1. Poor mating of connector halves or terminals not fully seated in the connector body.
2. Improperly formed or damaged terminals. All connector terminals in a suspect circuit should be carefully reformed to increase contact tension.
3. Poor terminal to wire connection. This requires removing the terminal from the connector body to inspect.
4. Pin presence in the connector assembly.
5. Proper ground connections. Check all ground connections for signs of corrosion, tight fasteners, or other potential defects. Refer to wiring diagram manual for ground locations.
6. If a visual check does not find the cause of the problem, operate the car in an attempt to duplicate the condition and record the Fault code.
7. Most failures of the ABS system will disable ABS function for the entire ignition cycle even if the fault clears before key-off. There are some failure conditions, however, which will allow ABS operation to resume during the ignition cycle in which a failure occurred if the failure conditions are no longer present. The following conditions may result in intermittent illumination of the ABS Warning Lamp. All other failures will cause the lamp to remain on until the ignition switch is turned off. Circuits involving these inputs to the CAB should be investigated if a complaint of intermittent warning system operation is encountered.
8. Low system voltage. If Low System Voltage is detected by the CAB, the CAB will turn on the ABS Warning Lamp until normal system voltage is achieved. Once normal voltage is seen at the CAB, normal operation resumes.
9. Additionally, any condition which results in interruption of electrical current to the CAB or modulator assembly may cause the ABS Warning Lamp to turn on intermittently.