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Service Brake Booster Indicator On: 2003

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  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 vehicle. Is the REDUCED BRAKE POWER message displayed for one minute before the SERVICE BRAKE BOOSTER message is displayed? If yes, go to next step. If no, go to step  4.
  3. Perform BRAKE ASSIST SYSTEM DIAGNOSIS  under TROUBLE SHOOTING. Did you find and correct the condition? If yes, go to step  12. If no, go to step  11.
  4. Disconnect the supplemental brake assist pump motor connector. See Fig 1. Test the ignition 1 circuit (Pink wire) between supplemental brake assist pump motor connector and SBA (15-amp) fuse in underhood junction block for an open or a short to ground. Did you find and correct the condition? If yes, go to step  12. If no, go to next step.
  5. 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  12. If no, go to next step.
  6. Test the engine on signal circuit (Dark Blue at generator; Black/White at supplemental brake assist pump motor) between supplemental brake assist pump motor connector and SBA (15-amp) fuse in underhood junction block for an open or a short to ground. Did you find and correct the condition? If yes, go to step  12. If no, go to next step.
  7. Test the vehicle speed signal circuit (Dark Green/White wire) between supplemental brake assist pump motor connector and instrument cluster for an open. Did you find and correct the condition? If yes, go to step  12. If no, go to next step.
  8. Test the supplemental brake assist signal circuit (Dark Blue wire) between supplemental brake assist pump motor connector and instrument cluster for an open or a short to voltage. Did you find and correct the condition? If yes, go to step  12. If no, go to next step.
  9. Reconnect the supplement brake assist pump motor connector. Disconnect the instrument panel cluster connector. Connect a DVOM from battery voltage to the supplemental brake assist signal circuit (Dark Blue wire). Turn the ignition to the Run position while observing the DVOM. Did the DVOM flash battery voltage? If yes, go to step  11. If no, go to next step.
  10. Replace the supplement brake assist pump motor. See SUPPLEMENT BRAKE ASSIST PUMP MOTOR  under REMOVAL & INSTALLATION. After repair, go to step  12.
  11. Replace instrument panel cluster. See INSTRUMENT PANEL CLUSTER under REMOVAL & INSTALLATION in appropriate ANALOG INSTRUMENT PANELS article in ACCESSORIES & EQUIPMENT. After repair, go to next step.
  12. Start the engine. Does the SERVICE BRAKE BOOSTER message stay on? If yes, go to step  2. If no, system is okay.
Fig 1: Identifying Supplemental Brake Assist Pump Motor
G00250014Courtesy of GENERAL MOTORS CORP.
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