Jeep Wagoneer/Commando/Cherokee 1984-1998

General Information


See Figures 1 and 2

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Fig. Fig. 1: Anti-lock brake system component locations

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Fig. Fig. 2: Schematic of the anti-lock brake system component connections

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).


This brake system uses a hydraulic accumulator which, when fully charged, contains brake fluid at very high pressure. Before disconnecting any hydraulic lines, hoses or fittings be certain that the accumulator pressure is completely relieved. Failure to depressurize the accumulator may result in personal injury and/or vehicle damage.

Certain components within the ABS system are not intended to be serviced or repaired individually. Only those components with removal and installation procedures should be serviced.
Both the external accumulator and the smaller accumulator within the pump contain high pressure nitrogen charges to assistance in pressurizing the system. The gas pressure is maintained even after fluid pressure in the system is reduced. Never puncture or attempt to disassemble either of these components.
Do not use rubber hoses or other parts not specifically specified for the ABS system. When using repair kits, replace all parts included in the kit. Partial or incorrect repair may lead to functional problems and require the replacement of components.
Lubricate rubber parts with clean, fresh brake fluid to ease assembly. Do not use lubricated shop air to clean parts; damage to rubber components may result.
Use only DOT 3 or its superceding brake fluid from an unopened container.
If any hydraulic component or line is removed or replaced, it may be necessary to bleed the entire system.
A clean repair area is essential. Always clean the reservoir and cap thoroughly before removing the cap. The slightest amount of dirt in the fluid may plug an orifice and impair the system function. Perform repairs after components have been thoroughly cleaned; use only denatured alcohol to clean components. Do not allow ABS components to come into contact with any substance containing mineral oil; this includes used shop rags.
The anti-lock ECM is a microprocessor similar to other computer units in the vehicle. Insure that the ignition switch is OFF before removing or installing controller harnesses. Avoid static electricity discharge at or near the controller.


Depressurize the ABS accumulator and master cylinder assembly before performing any service operations. Failure to completely relieve the system could result in brake fluid under high pressure being sprayed on the technician and the vehicle. This can result in serious personal injury and vehicle damage.

  1. Turn the ignition switch OFF and leave it OFF during repairs, unless specifically directed otherwise.
  3. Firmly apply and release the brake pedal a minimum of 45-50 times.
  5. The pedal feel will become noticeably harder when the accumulator is completely discharged.
  7. 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.

  1. 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.

  1. Depressurize the system.
  3. Inspect the brake fluid level in the reservoir.
  5. Inspect brake lines, hoses, master cylinder assembly, brake calipers and cylinders for leakage.
  7. Visually check brake lines and hoses for excessive wear, heat damage, punctures, contact with other parts, missing clips or holders, blockage or crimping.
  9. Check the calipers and wheel cylinders for rust or corrosion. Check for proper sliding action, if applicable.
  11. Check the caliper and wheel cylinder pistons for freedom of motion during application and release.
  13. Inspect the wheel speed sensors for proper mounting and connections.
  15. Inspect the tone wheels for broken teeth or poor mounting.
  17. Inspect the wheels and tires on the vehicle. They must be of the same size and type to generate accurate speed signals.
  19. 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.
  21. 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.