Flow of Diagnosis

INTRODUCTION
These procedures include all the specifications, instructions, and graphics needed to diagnose Mark 20 Antilock Braking System (ABS) problems. These diagnostics are based on the failure condition or symptom being present at time of diagnosis.

Follow the recommendations below when choosing your diagnostic path.

1 First make sure the DRBIII is communicating with the CAB. If the DRBIII displays a "No Response" condition, you must diagnose that first.
2 Read DTC's (diagnostic trouble codes) with the DRBIII.
3 If no DTC's are present, identify the customer complaint.
4 Once the DTC or customer complaint is identified, locate the matching test in Diagnostic Tests and begin to diagnose the symptom. Manufacturer Code Charts

An * placed before the symptom description indicated a customer complaint.

When repairs are required, refer to the appropriate components for the proper removal and repair procedure. Diagnostic procedures change every year. New diagnostic systems may be added; carryover systems may be enhanced.

DIAGNOSIS AND TESTING - ANTILOCK BRAKES
The ABS brake system performs several self-tests every time the ignition switch is turned on and the vehicle is driven. The CAB monitors the systems input and output circuits to verify the system is operating correctly. If the on board diagnostic system senses that a circuit is malfunctioning the system will set a trouble code in its memory.

NOTE: An audible noise may be heard during the self-test. This noise should be considered normal. The MDS or DRB III scan tool is used to diagnose the ABS system.