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HOMESERVICE MANUALSCHEVROLET1998SUBURBAN K2500, 7.4 J, PART TIMEREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 400 (CHARGING SYSTEM)DIAGNOSTIC TESTSDTC P0622: IMPROPER PULSE WIDTH MODULATED SIGNALDIAGNOSTIC PROCEDURE
1998 Chevrolet Suburban K2500, 7.4 J, Part Time

Diagnostic Procedure

1998 Chevrolet Suburban K2500, 7.4 J, Part TimeSECTION Diagnostic Procedure
WARNING: This page is about a different car, the 2003 Oldsmobile Aurora and 2002 Oldsmobile Aurora. However, it is still accessible from the selected car via links, so may be relevant.
  1. If engine electrical diagnostic system check was performed, go to next step. If engine electrical diagnostic system check was not performed, go to ENGINE ELECTRICAL DIAGNOSTIC SYSTEM CHECK  under ON-VEHICLE TESTING.
  2. Connect scan tool to Data Link Connector (DLC). See COMPONENT LOCATIONS  . Start engine. Using scan tool, observe GEN F-Terminal parameter in PCM data list. If GEN F-Terminal parameter is within 5-95 percent, go to next step. If GEN F-Terminal parameter is not within 5-95 percent, go to step  4 .
  3. Using scan tool, command generator Off. If GEN F-Terminal is not 0 percent, go to next step. If GEN F-Terminal is 0 percent, problem may be intermittent. Check wiring and connections, see PRELIMINARY INSPECTION  under TROUBLE SHOOTING.
  4. Turn ignition switch to OFF position. Disconnect generator 4-pin harness connector. Start engine. Using DVOM measure voltage between ground and generator turn-on signal circuit, generator harness connector terminal "B" (Red wire). Using scan tool, command generator On and Off. With generator off voltage reading should be 0 volts. With generator On, voltage reading should be 5 volts. If voltage reading is as specified, go to next step. If voltage reading is not as specified, go to step  6 .
  5. Turn ignition switch to RUN position. Using test light connect to battery voltage, repeatedly probe generator field duty cycle signal circuit, generator harness connector terminal "C" (Gray wire), while observing GENERATOR PWM on scan tool. If GENERATOR PWM display is affected, go to step  8 . If not, go to step  7 .
  6. Test generator turn-on signal circuit, generator harness connector terminal "B" (Red wire), for a short or an open. If problem exists, repair circuit as necessary and go to step  11 . If no problem exists, go to step  9 .
  7. Test generator field duty cycle signal circuit, generator harness connector terminal "C" (Gray wire), for a short or an open. If problem exists, repair circuit as necessary and go to step  11 . If no problem exists, go to step  9 .
  8. Inspect generator harness connector for poor connections. If problem exists, repair circuit as necessary and go to step  11 . If no problem exists, go to TEST A: CHARGING SYSTEM TEST  under SYSTEM TESTS.
  9. Inspect PCM harness connector for poor connections. If no problem exists, go to next step. If problem exists, repair circuit as necessary and go to step  11 .
  10. Replace PCM. After replacement, reprogram PCM. See REMOVAL & INSTALLATION article in ENGINE PERFORMANCE. After repairs are made, go to next step.
  11. Review and record scan tool fail records data. Using scan tool, clear DTCs. Start engine. Using scan tool, observe specific DTC information for DTC P0622 until test runs. If scan tool indicates DTC P0622 passed this ignition, system is okay. If scan tool indicates DTC P0622 failed this ignition, go to step  2 .
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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.