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HOMESERVICE MANUALSGMC1999FORWARD CONTROL 4.3 W, STANDARDREPAIR AND DIAGNOSIS (SINGLE PAGE)ELECTRICALSTARTERSTARTING SYSTEMON-VEHICLE TESTINGENGINE DOES NOT CRANK, STARTER SOLENOID DOES NOT CLICK"S" & "T" SERIES
1999 GMC Forward Control 4.3 W, Standard

"S" & "T" Series

1999 GMC Forward Control 4.3 W, StandardSECTION "S" & "T" Series
  1. Connect a DVOM between starter solenoid connector terminal "S" (Purple wire) and engine ground. Place gear selector in Park (A/T), or depress and hold clutch pedal (M/T). Turn ignition switch to START position and observe DVOM. If reading is 12 volts or more, go to step  13. If reading is less than 12 volts, go to next step.
  2. Remove starter relay from underhood fuse-relay center. See COMPONENT LOCATIONS  table. Connect a test light between starter relay socket terminal No. 30 (Red wire) and ground. If test light illuminates, go to next step. If test light does not illuminate, go to step  14.
  3. With ignition in START position, connect test light to starter relay cavity for terminal No. 85. If test light illuminates, go to next step. If test light does not illuminate, go to step  15.
  4. Connect DVOM between starter relay cavities for starter relay terminals No. 85 and 86. Turn ignition to START position. If reading is greater than 9.5 volts, go to next step. If reading is less than 9.5 volts, go to step  16.
  5. Place gear selector in Park (A/T), or depress and hold clutch pedal (M/T). Connect a DVOM between starter relay cavity No. 85 (Purple/White wire) and engine ground. Turn ignition switch to START position. If reading is 9.5 volts or more, go to next step. If reading is less than 9.5 volts, go to step  17.
  6. If vehicle is equipped with a manual transmission, go to next step. If vehicle is equipped with an automatic transmission, go to step  9.
  7. Disconnect Clutch Pedal Position (CPP) switch connector. Turn ignition switch to START position. Using DVOM, check voltage between CPP switch wiring harness connector cavity "A" (Purple wire) and ground. If reading is more than 9.5 volts, go to next step. If reading is 9.5 volts or less, go to step  11.
  8. Connect a fused jumper wire across CPP switch wiring harness connector cavities "A" (Purple wire) and "C" (Purple/White wire). Turn ignition switch to START position. If starter cranks engine, go to step  18. If starter does not crank engine, go to step  19.
  9. Disconnect Park Neutral Position (PNP) switch connector. Turn ignition switch to START position. Using DVOM, measure voltage between PNP switch wiring harness connector C1 terminal "E" (Purple wire) and ground. If reading is more than 9.5 volts, go to next step. If reading is 9.5 volts or less, go to step  11.
  10. Connect a fused jumper wire across PNP switch harness connector cavities "E" (Purple wire) and "G" (Purple/White wire). Turn ignition switch to START position. If starter cranks engine, go to step  20. If starter does not crank engine, go to step  21.
  11. Turn ignition switch to START position. Check voltage between ignition switch connector C211 cavity D1 (Yellow wire) and ground. See Figure. If reading is more than 9.5 volts, go to step  22. If reading is 9.5 volts or less, go to next step.
  12. Check voltage between ignition switch connector C211 cavity D5 (Orange wire) and ground. If reading is more than 9.5 volts, go to step  23. If reading is 9.5 volts or less, go to step  24.
  13. Clean starter motor mounting bolts, starter motor and mounting surface, and repeat test. If starter still does not operate, replace starter.
  14. Repair open in Red wire between starter relay and IGN A (40-amp) fuse in underhood fuse-relay center. Reinstall starter relay. Recheck system.
  15. Repair open in Purple wire between starter relay cavity No. 85 and starter solenoid. Reinstall starter relay. Recheck system.
  16. Repair open in Black wire between starter relay and ground. Reinstall starter relay. Recheck system.
  17. Replace starter relay. Recheck system.
  18. Adjust CPP switch. Repeat test. If starter does not crank engine, replace CPP switch. Recheck system.
  19. Repair open in Purple wire between starter relay and CPP switch. Recheck system.
  20. Replace PNP switch. Recheck system.
  21. Repair open in Purple wire between starter relay and PNP switch. Recheck system.
  22. Check for open in Yellow wire between ignition switch and underhood fuse-relay center connector C1 terminal D3. Repair as needed. If circuit is okay, repair open in Purple wire between underhood fuse-relay center connector C1 terminal C3 and CPP switch terminal "A" (M/T), or PNP switch connector terminal "E" (A/T). Recheck system.
  23. Replace ignition switch. Recheck system.
  24. Repair open in Orange wire between ignition switch and underhood fuse-relay center. Recheck system.
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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.