VISUAL INSPECTION

Before diagnosing an apparent ABS problem, 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.

1. Inspect the tire pressures; they must be approximately equal for the system to operate correctly.
2. Inspect the brake fluid level in the reservoir.
3. Inspect brake lines, hoses, master cylinder assembly and brake calipers or wheel cylinders for leakage.
4. Visually check brake lines and hoses for excessive wear, heat damage, punctures, contact with other parts, missing clips or holders, blockage or crimping.
5. Check the calipers and wheel cylinders for rust or corrosion. Check for proper sliding action if applicable.
6. Check the caliper and wheel cylinder pistons for freedom of motion during application and release.
7. Inspect the wheel speed sensors for proper mounting and connections.
8. Inspect the sensor wheels for broken teeth or poor mounting.
9. Inspect the wheels and tires on the vehicle. They must be of the same size and type to generate accurate speed signals.
10. Confirm the fault occurrence. Certain driver induced faults, such as not releasing the parking brake fully, will set a fault code and/or trigger the dash warning light. Excessive wheel spin on low-traction surfaces may be read as a fault by the ECU. High speed acceleration or riding the brake pedal may also set fault codes and/or trigger a warning lamp. These induced faults are not system failures, but examples of vehicle performance outside the parameters of the control unit.
11. 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. Incorrect adjustment of the wheel speed sensor will cause a loss of wheel speed signal. Check harness and component connectors carefully.