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HOMESERVICE MANUALSGMC1999FORWARD CONTROL 5.7 R, AUTOMATICREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 170 (BODY CONTROL MODULES)SYSTEM TESTSTEST C: POWER MODE MISMATCHTEST PROCEDURE
1999 GMC Forward Control 5.7 R, Automatic

Test Procedure

1999 GMC Forward Control 5.7 R, AutomaticSECTION Test Procedure
WARNING: This page is about a different car, the 2002 Oldsmobile Aurora. However, it is still accessible from the selected car via links, so may be relevant.
NOTE: Leave driver door open during this test. This will disable retained accessory power mode, and eliminate this information from power mode parameter list.
  1. Connect scan tool to Data Link Connector (DLC). DLC is located below driver side of instrument panel, near steering column. Turn ignition switch to OFF position. Using scan tool, observe CLASS 2 POWER MODE parameter in DIAGNOSTIC CIRCUIT CHECK menu. If displayed power mode parameter matches actual ignition switch position, go to next step. If displayed power mode parameter does not match actual ignition switch position, go to step  6.
  2. Turn ignition switch to OFF position, and ensure ignition key is in ignition switch. Using scan tool, observe CLASS 2 POWER MODE parameter in DIAGNOSTIC CIRCUIT CHECK menu. If displayed power mode parameter matches actual ignition switch position, go to next step. If displayed power mode parameter does not match actual ignition switch position, go to step  6.
  3. Turn ignition switch to RUN position. Using scan tool, observe CLASS 2 POWER MODE parameter in DIAGNOSTIC CIRCUIT CHECK menu. If displayed power mode parameter matches actual ignition switch position, go to next step. If displayed power mode parameter does not match actual ignition switch position, go to step  6.
    4. CAUTION: Engine may start during this procedure. Turn ignition switch to OFF position after verifying power mode.
  4. Turn ignition switch to START position. Using scan tool, observe CLASS 2 POWER MODE parameter under DIAGNOSTIC CIRCUIT CHECK menu. If displayed power mode parameter matches actual ignition switch position, go to next step. If displayed power mode parameter does not match actual ignition switch position, go to step  6.
  5. Turn ignition switch to ACC position. Using scan tool, observe CLASS 2 POWER MODE parameter in DIAGNOSTIC CIRCUIT CHECK menu. If displayed power mode parameter does not match actual ignition switch position, go to next step. If displayed power mode parameter matches actual ignition switch position, inspect for intermittents. See INTERMITTENTS .
    6. CAUTION: Engine may start during this procedure. Turn ignition switch to OFF position after verifying power mode IGNITION input status.
  6. Turn ignition switch to OFF position. Disconnect Dash Integration Module (DIM) connector C3. DIM is located behind passenger side of dash, near blower motor. Turn and hold ignition switch to position that indicated incorrect power mode. Using a test light connected to ground, probe DIM connector IGNITION inputs (DIM harness connector C3 terminals A1, A2, A3 and B1). See Figure. If test light illuminates only at proper inputs specified for ignition switch, go to next step. For correct IGNITION input status, see POWER MODES . If voltage exists at inputs not specified for ignition switch position, go to step  8.
    7. CAUTION: Engine may start during this procedure. Turn ignition switch to OFF position after verifying power mode.
  7. Turn and hold ignition switch to position that indicated incorrect power mode. Using a test light connected to ground, probe DIM connector IGNITION inputs. If voltage does not exist on any inputs specified for ignition switch position, go to step  9. If voltage exists on all inputs specified for ignition switch position, go to step  11.
  8. Disconnect ignition switch harness connectors. See IGNITION SWITCH under REMOVAL & INSTALLATION in INSTRUMENT PANELS - AURORA article. Inspect ignition switch input circuits between ignition switch harness connectors and DIM (DIM harness connector C3 terminals A1, A2, A3 and B1) for a short to voltage. Inspect ignition switch input circuits for a short between circuits. See WIRING DIAGRAMS . If problem does not exist, go to step  10. If problem exists, repair ignition switch input circuits as necessary. After repair, go to step  14.
  9. Disconnect ignition switch harness connectors. Inspect ignition switch input circuits between ignition switch and DIM (DIM harness connector C3 terminals A1, A2, A3 and B1) for an open. See WIRING DIAGRAMS . If problem does not exist, go to next step. If problem exists, repair ignition switch input circuits as necessary. After repair, go to step  14.
  10. Inspect ignition switch harness connectors for poor connections and terminal tension. If problem does not exist, go to step  12. If problem exists, repair ignition switch harness connectors as necessary. After repair, go to step  14.
  11. Inspect DIM harness connector for poor connections and terminal tension. If problem does not exist, go to step  13. If problem exists, repair DIM harness connector as necessary. After repair, go to step  14.
  12. Replace ignition switch. See IGNITION SWITCH under REMOVAL & INSTALLATION in INSTRUMENT PANELS - AURORA article. After repair, go to step  14.
  13. Replace DIM. See DASH INTEGRATION MODULE . Program DIM. See DASH INTEGRATION MODULE  under PROGRAMMING. After repair, go to next step.
    14. CAUTION: Engine may start during this procedure. Turn ignition switch to OFF position after verifying power mode.
  14. Connect all disconnected components. Using scan tool, observe CLASS 2 POWER MODE under DIAGNOSTIC CIRCUIT CHECK menu. Cycle ignition switch through all positions. If displayed power mode parameter does not match actual ignition switch position, repeat test beginning at step  1.
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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.