Hydraulic Control Assembly - Antilock Brakes: Service and Repair
Brake Pressure Modulator Valve Replacement
Removal Procedure
Caution: Unless directed otherwise, the ignition and start switch must be in the OFF or LOCK position, and all electrical loads must be OFF before servicing any electrical component. Disconnect the negative battery cable to prevent an electrical spark should a tool or equipment come in contact with an exposed electrical terminal. Failure to follow these precautions may result in personal injury and/or damage to the vehicle or its components.
For Vehicles equipped with OnStar� (UE1) with Back Up Battery:
The Back Up Battery is a redundant power supply to allow limited OnStar� functionality in the event of a main vehicle battery power disruption to the VCIM (OnStar�module). Do not disconnect the main vehicle battery or remove the OnStar� fuse with the ignition key in any position other than OFF. Retained accessory power (RAP) should be allowed to time out or be disabled (simply opening the driver door should disable RAP) before disconnecting power. Disconnecting power to the OnStar� module in any way while the ignition is On or with RAP activated may cause activation of the OnStar� Back-Up Battery (BUB) system and will discharge and permanently damage the back-up battery. Once the Back-Up Battery is activated it will stay on until it has completely discharged. The BUB is not rechargeable and once activated the BUB must be replaced.
1. Remove the negative battery cable.
Important: The area around the electric hydraulic control unit (EHCU) MUST be free from loose dirt to prevent contamination of disassembled ABS components.
2. Thoroughly wash all contaminants from around the EHCU.
3. Disconnect the three electrical harness connectors from the electronic brake control module (EBCM).
Important: Make sure that brake lines are tagged and kept in order for proper reassembly.
4. Disconnect the 5 brake lines from the brake pressure modulator valve (BPMV). When looking at the brake pipe port face of the BPMV, the ports are assigned as follows:
- Upper Left--Left Front Output.
- Upper Middle--Right Front Output.
- Upper Right--Rear Output.
- Lower Left--Master Cylinder Secondary/Front Input.
- Lower Right--Master Cylinder Primary/Front Input.
5. Remove the 3 bolts (4) securing the EHCU mounting bracket (3) to the frame rail (5).
6. Remove the EHCU (1) from the vehicle.
7. Remove the 2 bolts (4) securing the BPMV mounting bracket (3) to the BPMV (1).
8. Disconnect the 2 way ABS pump motor connector.
9. Remove the four T-25 TORX� bolts from the EBCM (2).
Important:
- Do not use a tool to pry the EBCM or the BPMV. Excessive force will damage the EBCM.
- Do not reuse the EBCM mounting bolts. Always install NEW bolts.
10. Remove the EBCM (2) from the BPMV (1). Removal may require a light amount of force.
11. Clean the EBCM to BPMV mounting surfaces with a clean cloth.
Installation Procedure
Notice: Use the correct fastener in the correct location. Replacement fasteners must be the correct part number for that application. Fasteners requiring replacement or fasteners requiring the use of thread locking compound or sealant are identified in the service procedure. Do not use paints, lubricants, or corrosion inhibitors on fasteners or fastener joint surfaces unless specified. These coatings affect fastener torque and joint clamping force and may damage the fastener. Use the correct tightening sequence and specifications when installing fasteners in order to avoid damage to parts and systems.
Important: Do not use RTV or any other type of sealant on the EBCM gasket or mating surfaces.
Important: Do not reuse the old mounting bolts. Always install NEW bolts with the new BPMV.
1. Install the EBCM (2) onto the BPMV (1).
2. Install the four EBCM bolts. Tighten the four bolts to 5 Nm (39 lb in) in an X-pattern.
3. Connect the 2 way ABS pump motor connector to the EBCM.
4. Install the BPMV (1) to BPMV bracket (3).
5. Install the BPMV to bracket retaining bolts (4). Tighten the bolts to 9 Nm (7 lb ft).
6. Install the EHCU (1, 2) to the vehicle frame (5). Tighten the three EHCU bracket bolts (4) to 25 Nm (18 lb ft).
7. Connect the two electrical harness connectors to the EBCM (1).
Important: The brake pipes are held in the proper place by a frame mounted plastic bracket. Ensure the brake pipes stay in the correct place for proper reassembly.
8. Install the 5 brake pipes to the BPMV (6). Tighten the brake pipe fittings to 30 Nm (22 lb ft).
9. Connect the negative battery cable.
10. Bleed the brake system.
11. Return to Diagnostic Starting Point.