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Home >> Oldsmobile >> 1996 >> Eighty-Eight Base >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control Systems Tests W/Codes >> Diagnostic Trouble Codes >> DTC P1643 - Fuel Pump Pulse Width Modulation (PWM) Control Circuit >> Diagnostic Procedures

Diagnostic Procedures

  1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. Turn ignition off. Disconnect PCM connectors. Turn ignition on. Using a DVOM, check voltage between engine ground and PCM harness connector fuel pump PWM driver circuit. If voltage is 9-16 volts, go to next step. If voltage is not as specified, go to step 6).
  3. Using DVOM in 10-amp scale, check current between engine ground and fuel pump PWM driver circuit for 2 minutes. If current remains 0.1-0.5 amp, go to step 11). If current does not remain as specified, go to next step.
  4. Turn ignition off. With PCM connectors disconnected, disconnect Fuel Pump Control Module (FPCM) connector. Turn ignition on. Using DVOM, check voltage between engine ground and fuel pump PWM driver circuit. If voltage is zero volts, go to step 10). If voltage is more than zero volts, go to next step.
  5. Locate and repair short to voltage in fuel pump PWM driver circuit, and go to step 18).
  6. Check fuel pump relay ignition feed circuit fuse. If fuse is blown, go to next step. If not, go to step 8).
  7. Repair short to voltage in fuel pump PWM control circuit. After repairs, go to step 18).
  8. Unplug FPCM Ignition on. Measure voltage between ground and ignition feed for module. If about battery voltage is present, go to next step. If about battery voltage is not present, go to step 13).
  9. Check fuel pump PWM driver circuit for an open or short to ground. Repair as necessary and go to step 18). If no problem exists, go to step 10).
  10. Check for poor FPCM control circuit connection at PCM connector or module. Check ignition feed circuit to module for poor connection at module connector. Repair as necessary and go to step 18). If no problem is present, go to step 14).
  11. Turn ignition off. Reconnect PCM connectors. Disconnect FPCM connector. Turn ignition on. Connect a test light between fuel pump PWM harness connector fuel pump PWM driver and ignition feed circuits. Using scan tool, cycle fuel pump PWM on and off. If test light flashes on and off, go to DIAGNOSTIC AIDS. If test light does not flash on and off, go to next step.
  12. Check fuel pump PWM driver circuit for faulty connection at PCM. If faulty connection is found, repair as necessary and go to step 18). If connection is okay, go to step 15).
  13. Repair open in ignition feed circuit to fuel pump relay or between relay and module and go to step 18).
  14. Replace FPCM and go to step 18).
  15. Replace PCM. Program replacement PCM using required equipment. Go to next step.
  16. Using scan tool, read and record FAIL RECORDS DATA, and clear DTCs. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P1643. If scan tool displays DTC P1643 FAILED THIS IGN, return to step 2). If scan tool does not display DTC P1643 FAILED THIS IGN, repair is complete.
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