GM Blazer/Jimmy/Typhoon/Bravada 1983-1993 Repair Guide

Component Replacement

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SYSTEM FILLING



The master cylinder is filled in the usual manner with no special procedures being necessary. Only DOT 3 brake fluid must be used; silicone or DOT 5 fluid is specifically prohibited. Do not use any fluid which contains a petroleum base; these fluids will cause swelling and distortion of the rubber parts within the system. Do not use old or contaminated brake fluid.

RWAL ECU



See Figure 1

The RWAL Electronic Control Unit (ECU), is a non-serviceable unit. It must be replaced when diagnosis indicates it is faulty. Because it is expensive and normally non-returnable, be absolutely sure the module is at fault before replacement.

  1. Turn the ignition switch OFF . The switch MUST be OFF whenever you are connecting/disconnecting power from the module. Failure to do this may destroy the computer.
  2.  
  3. Disengage the wiring harness connector(s) from the ECU.
  4.  
  5. Grasp the unit and remove it by pulling toward the front of the vehicle. If necessary, gently pry the tab at the rear of the unit while pulling.
  6.  



Click image to see an enlarged view

Fig. Fig. 1: RWAL ECU mounting

Do not touch the electrical connectors or pins; do not allow them to contact brake fluid. If contaminated with brake fluid, clean them with a small amount of water followed by isopropyl alcohol.

To install:
  1. Install the ECU by aligning it and carefully sliding it into the bracket until the tab locks into the hole.
  2.  
  3. Engage the wiring harness connector(s) to the unit.
  4.  
  5. Turn the ignition ON , then verify proper system operation.
  6.  

ANTI-LOCK PRESSURE CONTROL VALVE



The Anti-Lock Pressure Valve (APV), formerly known as the isolation/dump or control valve assembly is not serviceable. The entire component must be replaced as an assembly should a malfunction be confirmed.

  1. Turn the ignition switch OFF . The switch MUST be OFF whenever you are connecting/disconnecting power from the module (as will be done later in this procedure). Failure to do this may destroy the computer.
  2.  
  3. Disconnect the brake line fittings at the valve, then immediately cap or plug all openings to prevent system contamination or excessive fluid loss. Remember to protect the surrounding paint work from damage by fluid spillage.
  4.  
  5. Disengage the bottom connector from the RWAL ECU. At NO time should you allow the APV to hang by the wiring.
  6.  

Do not touch the electrical connectors or pins; do not allow them to contact brake fluid. If contaminated with brake fluid, clean them with a small amount of water followed by isopropyl alcohol.

  1. Remove the bolts holding the valve to the bracket.
  2.  
  3. Remove the valve from the vehicle.
  4.  

To install:
  1. Place the valve in position and install the retaining bolts. Tighten the bolts to 21 ft. lbs. (29 Nm).
  2.  
  3. Engage the electrical connector to the RWAL ECU.
  4.  

Before engaging the electrical connector, double check to be sure there is NO brake fluid on the terminals or the control module may be damaged. If necessary, clean the terminals with water, followed by denatured alcohol.

  1. Remove the caps or plugs, then install the brake lines and tighten the fittings to 18 ft. lbs. (24 Nm)
  2.  
  3. Properly bleed the RWAL hydraulic brake system at all 4 wheels.
  4.  

SPEED SENSOR



See Figure 2

The speed sensor is not serviceable and must replaced if malfunctioning. The sensor is usually located in the left rear of the transmission case on 2wd vehicles and on the transfer case of 4wd vehicles.

The speed sensor may be tested with an ohmmeter; the correct resistance is normally 900-2000 ohms. To remove the speed sensor:



Click image to see an enlarged view

Fig. Fig. 2: Common speed sensor mounting locations

  1. Raise and support the vehicle safely using jackstands.
  2.  
  3. Disengage the electrical connector from the speed sensor.
  4.  
  5. If used, remove the sensor retaining bolt.
  6.  
  7. Remove the speed sensor; have a container handy to catch fluid when the sensor is removed.
  8.  

If equipped with the 4L60-E automatic transmission, use J-38417 or an equivalent speed sensor remover/installer tool whenever the sensor is serviced.

  1. Recover the O-ring used to seal the sensor; inspect it for damage or deterioration.
  2.  

To install:
  1. When installing, coat the new O-ring with a thin film of fluid (transmission or transfer case fluid as applicable).
  2.  
  3. Install the O-ring and speed sensor.
  4.  
  5. If a retaining bolt is used, tighten the bolt to 97 inch lbs. (11 Nm) in automatic transmissions or 107 inch lbs. (12 Nm) for manual transmissions.
  6.  
  7. If the sensor is a screw-in unit tighten it to 32 ft. lbs. (43 Nm).
  8.  
  9. Engage the wire harness to the sensor.
  10.  
  11. Remove the jackstands and carefully lower the vehicle.
  12.  

 
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