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Home >> Chevrolet >> 2002 >> Impala LS >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System Self-Diagnostics - 3.8L >> Diagnostic Tests >> DTC P0620: Generator Performance >> Diagnostic Procedures
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Diagnostic Procedures

  1. Perform Diagnostic System Check - Engine Controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS  under SELF-DIAGNOSTIC SYSTEM. After performing Diagnostic System Check - Engine Controls, go to next step.
  2. Install scan tool. Start engine. Using scan tool, observe GENERATOR PWM parameter in PCM data list. Does the scan tool indicate GENERATOR PWM parameter is 5-95 percent? If yes, go to next step. If no, go to step  4.
  3. Using scan tool, command generator off. Does the GENERATOR PWM equal zero percent? If yes, see INTERMITTENT CONDITIONS  under SELF-DIAGNOSTIC SYSTEM. If no, go to next step.
  4. Turn ignition off. Disconnect generator harness connector. Start engine. Measure the voltage between the generator turn on signal circuit and a known-good ground. With the scan tool command the generator on and off. Is the voltage equal to zero volts with the generator off and equal to 5 volts with the generator on? If yes, go to next step. If no, go to step  6.
  5. Turn ignition on, engine off. Using a test light connected to battery voltage, repeatedly probe the generator field duty cycle signal circuit in the harness connector while monitoring the GENERATOR PWM on scan tool. Is the GENERATOR PWM display is affected? If yes, go to step  8. If no, go to step  7.
  6. Test the generator turn on signal circuit for a short or open. Did you find and correct the condition? If yes, go to step  11. If no, go to step  9.
  7. Test the generator field duty cycle signal circuit for a short or open. Did you find and correct the condition? If yes, go to step  11. If no, go to step  9.
  8. Inspect for poor connections at the harness connector of the generator. Did you find and correct the condition? If yes, go to step  11. If no, see appropriate GENERATORS & REGULATORS article in STARTING & CHARGING SYSTEMS.
  9. Inspect for poor connections at the harness connector of the PCM. Did you find and correct the condition? If yes, go to step  11. If no, go to next step.
  10. Replace PCM. Program replacement PCM. See POWERTRAIN CONTROL MODULE  under PROGRAMMING. After repairs, go to next step.
  11. Review and record scan tool FREEZE FRAME/FAILURE RECORDS data. Clear any DTCs. Operate vehicle within Conditions for Running DTC. Using scan tool, monitor SPECIFIC DTC INFO for this DTC. Does the scan tool indicate this DTC failed this ignition cycle? If yes, go to step  2. If no, system is okay.
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