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Home >> Oldsmobile >> 1997 >> Regency >> Repair and Diagnosis (Single Page) >> 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. See the BASIC TESTING - 3.8L article. 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. Remove fuel pump relay. Using a jumper wire, connect fuel pump relay cavities No. 30 and 87. Turn ignition on. Using a DVOM, check voltage between engine ground and PCM harness connector fuel pump PWM driver circuit. If battery voltage exists, 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 greater than zero volts, go to next step.
  5. Locate and repair short to voltage in fuel pump PWM driver circuit. After repairs, go to step  18.
  6. Check fuel pump relay ignition feed circuit fuse. If fuse is blown, go to next step. If fuse is okay, go to step  8.
  7. Repair short to ground in fuel pump PWM control circuit. After repairs, go to step  18.
  8. Disconnect FPCM connector. Turn ignition on. Measure voltage between ground and ignition feed for FPCM. If about battery voltage is present, go to next step. If about battery voltage is not present, go to step  11.
  9. Check fuel pump PWM driver circuit for an open or short to ground. If problem is found, repair as necessary then go to step  18. If circuit is okay, go to next step.
  10. Check for poor FPCM control circuit connection at PCM connector and FPCM. Check ignition feed circuit to FPCM for poor connection at module connector. If problem is found, repair as necessary then 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 step  16. 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 then 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. After repairs, go to step  18.
  14. Replace FPCM. After replacing module, go to step  18.
  15. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to step  18.
  16. Check for poor connections at fuel pump relay. If problem is found, repair as necessary then go to step  18. If problem is not found, go to next step.
  17. Replace fuel pump relay, then go to next step.
  18. 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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