Jeep Wrangler/YJ 1987-1995 Repair Guide

Diagnostic Procedures


See Figure 1

ABS diagnosis involves three basic steps. The first is observing the warning light display. Two warning lights are used and are visible in the instrument cluster. The standard brake system light is red and the anti-lock system light is amber. The amber ABS light is in a circuit with the ECU, and operates independently of the red brake light. The amber light indicates anti-lock system condition. It is in a circuit with the valve body solenoids and the main relay. The light flashes at start-up for self check, then goes out when the self-check program determines the system operation is normal. If an ABS fault code occurs either during the start-up self-check, or during normal operation, the amber light remains on until the fault is corrected.

The second step is a visual examination for low fluid, leaks, parking brakes applied or obvious damaged system components or wires.

The final diagnostic step involves the use of a Diagnostic Readout Box (DRB II) scan tool which is designed to determine the specific circuit or component at fault. The tester consists of a small microcomputer and a cartridge containing all tests it must perform. The tester is connected to the ABS diagnostic connector, located at the driver's side of the center console, under the instrument panel, in the passenger compartment. Reference to the DRB II scan tool guide must be made for the test procedures. Initial faults should be cleared and the vehicle road tested to reset any faults that remain in the system. Fault codes can be cleared with the DRB II scan tool.

Except for the second diagnostic step (which involves a visual examination for low fluid, leaks, and obvious damage to system components or wires), diagnosing the ABSmust be performed with the use of a Diagnostic Readout Box (DRB II) scan tool or its equivalent. This tool was specifically designed for this purpose and is recommended by Chrysler Corporation.

Refer to the ABS Fault Diagnosis Chart as a guide for potential system faults.

Click image to see an enlarged view

Fig. Fig. 1: ABS Fault Diagnosis Chart