Accessing and Reading Diagnostic Trouble Codes

This system contains a sophisticated on-board diagnostic system that can be accessed with a bidirectional SCAN tool. To properly diagnose the ABS system, a SATURN bidirectional scan tool or equivalent is necessary. The scan tool can be used to identify system faults as specifically as possible including whether or not the fault is intermittent. The scan tool can also be used to monitor the input and output signals of the Anti-Lock Brake Control Module (ABCM), manually control system components and perform automated functional tests. Using the scan tool allows for accurate fault confirmation and repair verification.

Before beginning any system diagnosis, it is important that a careful visual and physical inspection be performed. Inspect all vacuum hoses for correct routing, pinches, cuts or disconnects. Inspect all wires in the engine compartment and to wheel speed sensors for proper routing and connections.

Intermittent malfunctions are a common source of misdiagnosis when accessing diagnostic trouble codes. Most intermittent malfunctions are caused by loose or damaged electrical wiring and connectors. The scan tool can be used in several ways to aid in intermittent diagnosis. Simply connect the scan tool to the ALDL connector with the engine not running, then manipulate wiring harnesses or components under the hood while observing the scan tool. Leaving scan tool connected to the ALDL connector, drive vehicle under conditions similar to those present when the ABS fault first occurred. If the problem seems to be related to certain parameters that can be checked with the scan tool, they should be checked at this time. If there does not seem to be any correlation between the problem and any specific circuit, the scan tool can be checked on each position, watching for a period of time to see if there is any change in the readings that would indicate an intermittent malfunction.

The ABCM has the ability to take a snapshot of data with the last diagnostic trouble code stored. This can be done using the Malfunction "Malf" History function of the scan tool and can be very useful when trying to diagnose an intermittent diagnostic trouble code.

To access diagnostic trouble codes, connect the SATURN scan tool or suitable equivalent to the ALDL connector located under the instrument panel. The scan tool can now communicate directly to the ABCM. Any diagnostic trouble code(s) stored in the ABCM memory can now be displayed. When an ABS fault is detected, the ABS telltale lamp is lit and diagnostic trouble code(s) are placed in the General Information Table (Current Diagnostic Trouble Codes). When the ignition is switched off, the current diagnostic trouble codes are moved to the Malf History Table (Past Diagnostic Trouble Codes) and cleared from the General Information Table (Current Diagnostic Trouble Codes).

Refer to Antilock Brake System/Testing and Inspection/Procedures/Diagnostic Charts for further information regarding specific Diagnostic Trouble Codes.