See Figures 1 and 2
The Bendix anti-lock braking system is available on 1989-91 Jeep Cherokee and Wagoneer vehicles (model designation XJ) with SelecTrac 4-wheel drive. Anti-lock Brake Systems (ABS) are designed to prevent wheel lockup under heavy braking conditions on virtually any type of road surface. The Jeep ABS limits wheel lockup by modulating the brake fluid pressure to the brakes at each wheel. A vehicle which is stopped without locking the wheels will normally stop in a shorter distance than a vehicle with locked wheels. Additionally, vehicle control can be maintained during hard braking because the front wheels do not lock. The Jeep system is an electronically operated, power assisted brake system controlled by an isolated Electronic Control Unit (ECU).
DEPRESSURIZING THE SYSTEM
- Turn the ignition switch OFF and leave it OFF during repairs, unless specifically directed otherwise.
- Firmly apply and release the brake pedal a minimum of 45-50 times.
- The pedal feel will become noticeably harder when the accumulator is completely discharged.
- Do not turn the ignition switch ON after depressurizing the system, unless service procedures specifically require it or all service operations have been performed.
After the reserve pressure is depleted, the fluid level in the reservoir will rise above the MAX fill mark. This is normal; the reservoir will not overflow unless the system was originally overfilled.
- Always wear safety goggles when disconnecting lines and fittings.
Before diagnosing an apparent ABS problem, make absolutely certain that the normal braking system is in correct working order. Many common brake problems (dragging shoe, 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. The steps should be performed in order.
- Depressurize the system.
- Inspect the brake fluid level in the reservoir.
- Inspect brake lines, hoses, master cylinder assembly, brake calipers and cylinders for leakage.
- Visually check brake lines and hoses for excessive wear, heat damage, punctures, contact with other parts, missing clips or holders, blockage or crimping.
- Check the calipers and 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 wheel speed sensors for proper mounting and connections.
- Inspect the tone wheels for broken teeth or poor mounting.
- Inspect the wheels and tires on the vehicle. They must be of the same size and type to generate accurate speed signals.
- Confirm the fault occurrence with the operator. 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 ECM.
- Many system shutdowns are due to loss of sensor signals to or from the ECM. 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.