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2004 Pickup

WARNING: This page does not describe the selected car, but rather 12 other vehicles, including the 2003 GMC Yukon XL, 2003 GMC Yukon, 2003 GMC Sierra, 2003 GMC Cab & Chassis Sierra, and 2003 Chevrolet Tahoe. However, it is still accessible from the selected car via links, so may be relevant.
  1. Did you review the brake warning system description and operation and the hydraulic brake assist system description and operation, then perform the necessary inspections? If so, go to next step. If not, see HYDRAULIC BRAKE SYSTEM  under GENERAL DIAGNOSIS under TROUBLE SHOOTING.
  2. Start the engine. Is the REDUCED BRAKE POWER message displayed within 5 seconds? If yes, go to REDUCED BRAKE POWER MESSAGE DISPLAYED . If no, go to next step.
  3. Is the service brake booster message displayed within 5 seconds? If yes, go to step  6. If no, go to next step.
  4. Operate the vehicle at a speed greater than 48 km/h. Is the SERVICE BRAKE BOOSTER message displayed? If yes, go to next step. If no, go to Diagnostic Aids.
  5. Test the charging system for proper operation. See appropriate CHARGING SYSTEM article in ELECTRICAL. Did you find and correct the condition? If yes, go to step  22. If no, go to step  21.
  6. Turn ignition off. Disconnect the supplemental brake assist pump motor connector. See Figure. Connect a test lamp between ignition 1 and a good ground. Turn on the ignition. Does the test lamp illuminate? If yes, go to next step. If no, go to step  12.
  7. Check Black and Black/White wires between supplemental brake assist pump motor connector and ground for an open. Did you find and correct the condition? If yes, go to step  22. If no, go to next step.
  8. Connect a test lamp between the engine ON signal circuit and a good ground. Does the test lamp illuminate? If yes, go to step  10. If no, go to next step.
  9. Repair the open in the engine ON signal circuit. After repair, go to step  22.
  10. Use a DMM to measure the voltage between the vehicle speed signal circuit and a good ground. Does the voltage measure greater than 10 volts? If yes, go to step  13. If no, go to next step.
  11. Repair the open in the vehicle speed signal circuit. After repair, go to step  22.
  12. Repair the open in the ignition 1 circuit. After repair, go to step  22.
  13. Use a DMM to measure the voltage between the supplemental brake assist circuit and a good ground. Does the voltage measure greater than 11 volts? If yes, go to step  16. If no, go to next step.
  14. Remove the IPC from the instrument panel. See INSTRUMENT PANEL CLUSTER under REMOVAL & INSTALLATION in appropriate ANALOG INSTRUMENT PANELS article in ACCESSORIES & EQUIPMENT. Test the supplemental brake assist signal circuit for an open. Did you find and correct the condition? If yes, go to step  22. If no, go to next step.
  15. Inspect for poor connections at the IPC harness connector. Did you find and correct the condition? If yes, go to step  22. If no, go to step  19.
  16. Connect a test lamp between the SBA signal circuit and a good ground. Does the test lamp illuminate? If yes, go to next step. If no, go to step  20.
  17. Turn OFF the ignition. Remove the IPC from the instrument panel. See INSTRUMENT PANEL CLUSTER under REMOVAL & INSTALLATION in appropriate ANALOG INSTRUMENT PANELS article in ACCESSORIES & EQUIPMENT. Turn ON the ignition. Connect a test lamp between the SBA signal circuit and ground. Does the test lamp illuminate? If yes, go to next step. If no, go to step  19.
  18. Repair the short to voltage in the SBA signal circuit. After repair, go to step  22.
  19. Replace instrument panel cluster. See INSTRUMENT PANEL CLUSTER under REMOVAL & INSTALLATION in appropriate ANALOG INSTRUMENT PANELS article in ACCESSORIES & EQUIPMENT. After repair, go to step  22.
  20. Inspect for poor connections at the SBA harness connector. Did you find and correct the condition? If yes, go to step  22. If no, go to next step.
  21. Replace the supplement brake assist pump motor. See SUPPLEMENT BRAKE ASSIST PUMP MOTOR  under REMOVAL & INSTALLATION. After repair, go to step.
  22. Start the engine. Does the SERVICE BRAKE BOOSTER message stay on? If yes, go to step  2. If no, system is okay.
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