ABS Diagnostic Trouble Codes

GENERAL INFORMATION
Diagnostic Trouble Codes (DTC) are kept in the controller's memory until either erased by the technician using the DRB or erased automatically after 3500 miles. DTC's are retained by the controller even if the ignition is turned off or the battery is disconnected. More than one DTC can be stored at a time. The key cycle number of occurrences and the DTC that was stored is also displayed. Most functions of the Controller Antilock Brakes (CAB) and the ABS system can be accessed by the technician for testing and diagnostic purposes by using the DRB.

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

INTERMITTENT DIAGNOSTIC TROUBLE CODES
As with virtually any electronic system, intermittent electrical problems in the ABS system may be difficult to accurately diagnose.

Most intermittent electrical problems are caused by faulty electrical connections or wiring. When an intermittent fault is encountered, check suspect circuits for:

A visual inspection for loose, disconnected, or misrouted wires should be done before attempting to diagnose or service the ITT Teves Mark 20 antilock brake system. A visual inspection will eliminate unnecessary testing and diagnostics time. A thorough visual inspection will include the following components and areas of the vehicle.
1. Inspect fuses in the Power Distribution Center (PDC) and the wiring junction block. Verify that all fuses are fully inserted into the PDC and wring junction block. A label on the underside of the PDC cover identifies the locations of the ABS fuses in the PDC.
2. Inspect the 25-way electrical connector at the CAB for damage, spread or backed-out wiring terminals. Verify that the 25-way connector is fully inserted in the socket on the CAB. Be sure that wires are not stretched tight or pulled out of the connector.
3. Verify that all the wheel speed sensor connections are secure.
4. Poor mating of connector halves or terminals not fully seated in the connector body.
5. Improperly formed or damaged terminals. All connector terminals in a suspect circuit should be carefully reformed to increase contact tension.
6. Poor terminal to wire connection. This requires removing the terminal from the connector body to inspect.
7. Pin presence in the connector assembly
8. 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.
9. Problems with main power sources of the vehicle. Inspect battery, generator, ignition circuits and other related relays and fuses.
10. 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 trouble code.
11. 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.
12. 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.
13. High system voltage. If high system voltage is detected by the CAB, the CAB will turn on the Amber ABS Warning Lamp until normal system voltage is achieved. Once normal voltage is again detected by the CAB, normal ABS operation resumes.
14. 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.
15. The body controller can turn on the (yellow) ABS warning lamp if CCD communication between the body controller and the CAB is interrupted.