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DTC P0620: Pcm Detects That The PWM Signal On The Generator Field Duty Cycle Signal Circuit Is Not Within The Expected Range: Testing

WARNING: This page is about a different car, the 2003 Buick Regal, 2003 Buick Century, 2002 Buick Regal, and 2002 Buick Century. However, it is still accessible from the selected car via links, so may be relevant.
  1. Did you perform the Engine Electrical Diagnostic System Check? If so, go to step  2 . If not, go to DIAGNOSTIC SYSTEM CHECK (ENGINE ELECTRICAL)  under SELF-DIAGNOSTIC SYSTEM.
  2. Install a scan tool. Start the engine. With a scan tool, monitor the DTC Information for DTC P0620 in Engine Controls. Does the scan tool indicate that DTC P0620 has passed? If so, testing for intermittent and poor connections in wiring systems. If not, go to step  3 .
  3. With a scan tool, command the GEN L-Terminal OFF and then ON. While commanding the GEN L-Terminal OFF and ON, observe the Ignition 1 Signal parameter. Does voltage change with each command? If so, go to step  6 . If no, go to step  4 .
  4. Turn ON the ignition, leaving the engine OFF. Disconnect the generator harness connector. Measure the voltage between the generator turn on signal circuit and ground. With a scan tool, command the GEN L-Terminal ON. Does the voltage measure near the specified value (5.0 volts)? If so, go to step  7 . If not, go to step  5 .
  5. Test the generator turn on signal circuit for a short or open. Did you find and correct the condition? If so, go to step  11 . If not, go to step  8 .
  6. Test the generator battery positive voltage sense circuit for a high resistance or open. Did you find and correct the condition? If so, go to step  11 . If not, go to step  7 .
  7. Inspect for poor connections at the harness connector of the generator. Did you find and correct the condition? If so, go to step  11 . If not, go to step  9 .
  8. Inspect for poor connections at the harness connector of the PCM. Test for intermittent and poor connections and connector repairs in wiring systems. Did you find and correct the condition? If so, go to step  11 . If not, go to step  10 .
  9. Replace the Generator. See GENERATOR under REMOVAL & INSTALLATION in STARTING & CHARGING article in CHARGING SYSTEMS IN ELECTRICAL. After repairs are complete, go to step  11 .
    10. CAUTION: The replacement PCM must be programmed. See POWERTRAIN CONTROL MODULE (PCM)  under PROGRAMMING.
  10. Replace the PCM. See POWERTRAIN CONTROL MODULE under COMPUTERIZED ENGINE CONTROLS in REMOVAL & INSTALLATION article in ENGINE PERFORMANCE. After repairs are complete, go to step  11 .
  11. Review and record the scan tool Fail Records data. Clear any DTCs. Operate the vehicle within the Fail Records conditions as noted. Using a scan tool, monitor the specific DTC info for DTC P0620. Does the scan tool indicate that DTC P0620 has failed this ignition? If so, go to step  2 . If not, system OK.
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