GM Corvette 1984-1996 Repair Guide

Modulator Valve

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REMOVAL & INSTALLATION



Due to safety reasons, the modulator valve must not be repaired; the complete unit must be replaced. The only exceptions to this are the pump motor relay and the solenoid relay. Both relays can be replaced. No screws on the modulator valve may be loosened. If the screws are loosened, it will not be possible to obtained leak-tight brake circuits.

On 1994-96 vehicles, the valve is referred to as the Brake Pressure Modulator (BPM) valve.

When replacing the modulator valve, it is accessed in the rear storage compartment. Make sure to protect the car's interior and exterior to avoid spilling brake fluid. Make sure the completely wipe up the brake fluid from the bottom of the storage compartment when replacing the modulator valve.

1986-91 Vehicles

See Figures 1, 2, 3, 4 and 5

  1. Disconnect the negative battery cable.
  2.  
  3. Remove the storage tray and insulation.
  4.  
  5. Disconnect and remove the entire ABS wiring harness from the storage compartment, as follows:
  6.  


WARNING
To prevent equipment damage, never connect or disconnect the wiring harness connector from the control module with the ignition switch in the ON position.

  1. Detach the control module wiring harness connector by depressing the spring clip under the neck of the connector, then pulling it out.
  2.  
  3. Remove the 2 screws from the wiring harness retention clip, then remove the retention clip from the wiring harness.
  4.  
  5. Detach the modulator valve wring harness connector.
  6.  
  7. Unplug the battery feed (red) wire connector from the wiring harness connector.
  8.  
  9. Detach the wheel speed sensor connectors from the wiring harness connector.
  10.  
  11. Remove the module relay from the bracket and detach the wiring harness connector.
  12.  
  13. Remove the wiring harness from the vehicle, noting the routing for installation.
  14.  



Click image to see an enlarged view

Fig. Fig. 1: View of the ABS wiring harness and module relay-1986-91 vehicles with Selective Ride Control (SRC)



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Fig. Fig. 2: ABS wiring harness and module relay locations-1986-91 vehicles without Selective Ride Control (SRC)

  1. Detach the modulator valve ground wire from the body wiring harness.
  2.  



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Fig. Fig. 3: Location of the modulator valve ground wire

  1. Disconnect and plug the brake pipes from the modulator valve, making sure to note their locations for installation.
  2.  



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Fig. Fig. 4: You MUST note the correct installed position and location of the brake pipes!

  1. Remove the 3 nuts attaching the modulator valve to the bracket.
  2.  

When removing the valve from the storage compartment, be careful not to spill any brake fluid.

  1. Remove the modulator valve. Clean any brake fluid from the bottom of the storage compartment.
  2.  
  3. If the valve is being replaced, remove the ground wire and insulators.
  4.  



Click image to see an enlarged view

Fig. Fig. 5: Exploded view of the modulator valve mounting-1986-91 vehicles

To install:
  1. If removed, install the ground wire and insulators.
  2.  
  3. Attach the modulator to the bracket and secure with the 3 retaining nuts. Tighten the nuts to 86 inch lbs. (10 Nm).
  4.  


WARNING
Make sure the brake lines are attached correctly. If the lines are accidentally switched, wheel lockup will occur. The only 2 ways this condition can be detected, is by using the ABS diagnostic tester or by performing an anti-lock stop.

  1. Connect the brake pipes to the modulator valve, in the proper locations noted during removal. If a new modulator is being installed, remove the shipping plugs from the valve openings. Tighten the brake pipes to 13 ft. lbs. (18 Nm).
  2.  
  3. Connect the modulator valve ground wire to the body wiring harness.
  4.  

When installing the ABS wiring harness, make sure that all connectors are securely connected. This will prevent system damage and malfunctions.

  1. Install the entire ABS wiring harness into the storage compartment, as follows:
  2.  

When installing the wiring harness, make sure that all connectors are securely connected and locked when necessary, Loose connectors can cause ABS malfunctions.

  1. Position the wiring harness in the vehicle, using the same routing noted during removal.
  2.  
  3. Attach the module relay connector, then place the relay in the bracket.
  4.  
  5. Connect the wheel speed sensor wiring to the wiring harness connector.
  6.  
  7. Attach the battery feed (red) wire connector to the wiring harness connector.
  8.  
  9. Connect the modulator valve electrical wiring.
  10.  
  11. Position the retention clip to the wiring harness and install the 2 retaining screws.
  12.  
  13. Attach the control module electrical connector, making sure the spring clip locks.
  14.  

  1. Fill the master cylinder reservoirs, then bleed the brake system, as outlined earlier in this section.
  2.  
  3. Install the insulation and storage tray.
  4.  
  5. Connect the negative battery cable, then perform the ABS system check as shown in the accompanying chart.
  6.  

1992-95 Vehicles
EXCEPT 1995 VIN P ENGINE

See Figures 6, 7 and 8

  1. Disconnect the negative battery cable.
  2.  
  3. Remove the rear storage compartment door and frame assembly.
  4.  
  5. Remove the sound insulator pad.
  6.  
  7. If equipped, detach the wire harness with the selective ride control module.
  8.  



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Fig. Fig. 6: View of the ABS/ASR wiring harness-1992 vehicle shown

  1. Remove the Electronic Brake Control Module (EBCM).
  2.  
  3. Note the installed location of the brake pipes, then disconnect them from the modulator valve. Plug or cap the lines to avoid excessive fluid loss.
  4.  

  1. Raise and safely support the vehicle.
  2.  
  3. Remove the modulator valve bracket-to-underbody cover bolts.
  4.  
  5. Carefully lower the vehicle, then remove the modulator valve.
  6.  



Click image to see an enlarged view

Fig. Fig. 7: Exploded view of the modulator valve-1992 vehicle shown, other years similar

  1. If the modulator valve is being replaced, remove the ground wire and bracket from the valve.
  2.  
  3. If the valve is being replaced, remove the pump motor and solenoid valve relays.
  4.  

To install:
  1. If removed, install the ground wire.
  2.  
  3. Position the modulator valve to the bracket and secure with the mounting bolts. Tighten to 86 inch lbs. (10 Nm).
  4.  
  5. Install the modulator valve.
  6.  
  7. Raise and safely support the vehicle, then install the modulator valve bracket to the underbody cover attaching bolts. Tighten the bolts to 86 inch lbs. (10 Nm).
  8.  
  9. Carefully lower the vehicle.
  10.  


WARNING
Make sure the brake lines are attached correctly. If the lines are accidentally switched, wheel lockup will occur. The only 2 ways this condition can be detected, is by using the ABS diagnostic tester or by performing an anti-lock stop.

  1. Connect the brake pipes to the modulator valve, in the proper locations noted during removal. If a new modulator is being installed, remove the shipping plugs from the valve openings. Tighten the brake pipes to 13 ft. lbs. (18 Nm).
  2.  



Click image to see an enlarged view

Fig. Fig. 8: During installation, connecting the brake lines properly is essential for system operation

  1. Install the EBCM.
  2.  
  3. If equipped connect the wiring harness with selective rid control module.
  4.  
  5. Connect the negative battery cable.
  6.  
  7. Fill the master cylinder reservoir, then bleed the master cylinder prime pipe and hydraulic brake system, as outlined earlier in this section.
  8.  

Always be sure the sound insulator pad covers the whole modulator or excessive noise could result during system operation.

  1. Install the sound insulator pad and rear storage compartment door and frame assembly.
  2.  

1995 VIN P Engine and 1996 Vehicles

See Figure 9

  1. Disconnect the negative battery cable.
  2.  
  3. Remove the rear storage compartment door and frame assembly.
  4.  
  5. Remove the sound insulator pad.
  6.  
  7. Detach the wire harness connector.
  8.  
  9. Remove the selective ride control module.
  10.  
  11. Remove the EBTCM bracket.
  12.  
  13. Note the location of the brake lines, then disconnect the lines from the BPM valve. Plug the lines to avoid excessive fluid loss.
  14.  
  15. Remove the BPM valve. Slide the BPM rearward out of the front insulators, leaving them attached to the underbody cover.
  16.  
  17. If the valve is being replaced, transfer the ground wire to the new valve and transfer the EBTCM to the new valve. Tighten the EBTCM-to-BPM bolts to 18 inch lbs. (2 Nm) and the insulator mounting bolt to 11 ft. lbs. (15 Nm).
  18.  


WARNING
Be careful not to damage the EBTCM seal.



Click image to see an enlarged view

Fig. Fig. 9: Exploded view of the BPM/EBTCM valve assembly-1995 VIN P engine and 1996 vehicles