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HOMESERVICE MANUALSGMC1999FORWARD CONTROL 5.7 R, AUTOMATICREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 83 (ENGINE CONTROLS - SELF-DIAGNOSTICS)DIAGNOSTIC TESTSDTC P0622: GENERATOR "F" TERMINAL CIRCUITDIAGNOSTIC PROCEDURES
1999 GMC Forward Control 5.7 R, Automatic

Diagnostic Procedures

1999 GMC Forward Control 5.7 R, AutomaticSECTION Diagnostic Procedures
WARNING: This page is about a different car, the 2002 Saturn LW200, 2002 Saturn L200, and 2002 Saturn L100. However, it is still accessible from the selected car via links, so may be relevant.
NOTE: If DTC P0621 is also set, diagnose that DTC first. See DTC P0621: GENERATOR "L" TERMINAL CIRCUIT  .
  1. Start engine. Using scan tool, monitor GENERATOR F TERMINAL DC. If scan tool reading is constantly zero percent, go to step  4 . If scan tool reading is constantly 99 percent, go to next step. If scan tool reading is not constantly zero or 99 percent, problem is intermittent. See DIAGNOSTIC AIDS  .
  2. Turn ignition off. Disconnect generator 2-pin harness connector. Turn ignition on, with engine off. If scan tool reading is zero percent, replace generator. If scan tool reading is not zero percent, go to next step.
  3. Using DVOM, measure voltage on Gray wire at connector. If voltage is more than 0.2 volt, repair short to voltage in Gray wire between PCM and generator. If voltage is not more than 0.2 volt, replace PCM.
  4. Turn ignition off. Disconnect generator 2-pin harness connector. Connect a test light between battery voltage and harness connector terminal No. 2 (Gray wire). Turn ignition on, engine off. Observe scan tool reading. If scan tool reading is not 99 percent, go to next step. If scan tool reading is 99 percent, check for loose connection at harness connector. Repair as necessary. If terminals are okay, replace generator.
  5. Turn ignition off. Disconnect PCM connector J2. Check continuity between Gray wire at generator connector and ground. If continuity exists, repair short to ground in Gray wire between PCM and generator. If continuity does not exist, check Gray wire for open. If wire is okay, replace PCM.
RENDER: 1.0x

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When to See a Mechanic

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.