Jeep Wagoneer/Commando/Cherokee 1984-1998

Hydraulic Control Unit (HCU)

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The Hydraulic Control Unit (HCU) on 1997-98 Jeep models also has the Controller Antilock Brakes (CAB) unit mounted to it. It serves the same function as the ABS-ECU does on 1995-96 models. The HCU/CAB is removed as an assembly.

Removal & Installation



See Figure 1

A Diagnostic Readout Box (DRB), or the equivalent type of scan tool, is essential to perform the bleeding of the ABS system.

  1. Disengage the vent hoses and air cleaner cover.
  2.  
  3. Loosen the clamp securing the air cleaner hose to the intake manifold and slide the clamp out of the way.
  4.  
  5. Remove the air cleaner cover, hose and filter.
  6.  
  7. Unfasten the air cleaner housing to panel bolts and nut, then remove the air cleaner housing.
  8.  
  9. Disengage the flex lines at the HCU.
  10.  
  11. Disengage the HCU solenoid harness from the main harness and the HCU pump motor harness.
  12.  
  13. Disengage the brake lines at the lower left side of the HCU.
  14.  
  15. If removing the HCU only:
    1. Remove the HCU solenoid by squeezing the connector fasteners with needle nose pliers then pulling them out of the bracket.
    2.  
    3. Unfasten the shoulder bolts attaching HCU to the bracket and remove the HCU.
    4.  

  16.  
  17. If removing the HCU and bracket:
    1. Unfasten the fasteners retaining the HCU to the bracket and remove the HCU.
    2.  

  18.  

To install:
  1. If only the HCU was removed:
    1. Install the HCU in the bracket and tighten the shoulder bolts.
    2.  
    3. Install the HCU solenoid by pressing the connector fasteners into the bracket.
    4.  

  2.  
  3. If installing the HCU and bracket as an assembly:
    1. Install the bracket on the studs and tighten the fasteners to 92-112 inch lbs. (10-13 Nm).
    2.  

  4.  
  5. Engage the HCU pump motor and solenoid harnesses.
  6.  
  7. Start the brake line fittings into the HCU by hand to avoid cross-threading and then tighten the fittings until they are snug.
  8.  
  9. Start the flex line fittings into the HCU by hand to avoid cross-threading and then tighten the fittings until they are snug.
  10.  
  11. Bleed the brake system. Refer to the proper procedure in this section.
  12.  
  13. Tighten the brake line fittings to 130-160 inch lbs. (15-18 Nm) at the HCU and master cylinder, and 160-210 inch lbs. (18-24 Nm) at the combination valve.
  14.  
  15. Install the air cleaner assembly, hoses and vacuum lines to the manifold.
  16.  
  17. Check the brake pedal action before moving the vehicle and bleed the brakes again if the pedal is not firm, (soft or spongy).
  18.  
  19. Test drive the vehicle and verify proper brake operation.
  20.  



Click image to see an enlarged view

Fig. Fig. 1: Exploded view of the HCU mounting

 
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