Before diagnosing an apparent ABS problem, check the battery condition; approximately 12 volts are required to operate the system. Turn the ignition switch ON and check that the ABS dashboard warning lamp comes on for 3-4 seconds. If the lamp does not come on, repair the fuse, bulb or wiring.
Also, make absolutely certain that the normal braking system is in correct working order. Many common brake problems (dragging parking brake, seepage, etc.) will affect the ABS system. A visual check of specific system components may reveal problems creating an apparent ABS malfunction. Performing this inspection may reveal a simple failure, thus eliminating extended diagnostic time. Perform the following checks before assuming an ABS problem:
- Check the tire pressures; they must be approximately equal for the system to operate correctly.
- Check the wheels and tires on the vehicle. They must be of the same size and type to generate accurate speed signals.
- Inspect the brake fluid level in the reservoir.
- Inspect the brake lines, hoses, master cylinder, brake calipers and cylinders for leakage.
- Check the brake lines and hoses for excessive wear, heat damage, punctures, contact with other parts, missing clips or holders, blockage or crimping.
- Inspect the calipers or wheel cylinders for rust or corrosion. Check for proper sliding action, if applicable.
- Check the caliper and wheel cylinder pistons for freedom of motion during application and release.
- Inspect the rear speed sensor for proper mounting and connections.
- Confirm an ABS fault occurrence. Certain driver induced faults, such as not releasing the parking brake fully, will set a fault code and trigger the dash warning light(s). Excessive wheel spin on low-traction surfaces, high speed acceleration or riding the brake pedal may also set fault codes and trigger a warning lamp. These induced faults are not system failures, but examples of vehicle performance outside the parameters of the control unit.
- Many system shutdowns are due to loss of sensor signals to or from the controller. The most common cause is not a failed sensor but a loose, corroded or dirty connector. Check harness and component connectors carefully.
See Figure 1
To obtain satisfactory self-diagnosing results, the vehicle must be driven in 2wd above 25 mph (40 km/h) for at least 1 minute. After the vehicle is stopped, the number of warning flashes is counted by grounding the check terminal, with the engine running.
If a malfunction occurs, the system will identify the problem, and the computer will assign and store a fault code for the fault(s). The dashboard warning lamp will be illuminated to inform the driver that a fault has been found.
During diagnostics, the system will transmit the stored code(s) by flashing the dashboard warning lamp. If two or more codes are stored, repair the first fault. After the first fault part or unit has been repaired, the warning lamp will then flash to indicate that the other part or unit is malfunctioning.
To obtain satisfactory self-diagnosing results, the vehicle must be driven in 2wd above 25 mph (40 km/h) for at least 1 minute. After the vehicle is stopped, the number of warning flashes is counted by grounding the check terminal (lower right corner of the check connector terminal to a body ground), with the engine running. The check connector is located under the dashboard to the left of the brake pedal. Refer to the following circuit diagram and diagnostic charts.
A stored code will be erased when the ignition is switched OFF . If the problem exists when the engine is restarted, the self-check will note the fault and again set the code.