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HOMESERVICE MANUALSCHEVROLET2008CHEVY EXPRESS G2500, VAN CARGO, 6.6 6REPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 28 (ENGINE CONTROL SYSTEM - SELF-DIAGNOSTICS)DIAGNOSTIC TESTSDTC P0505: IDLE CONTROL SYSTEMDIAGNOSTIC PROCEDURES
2008 Chevrolet Chevy Express G2500, Van Cargo, 6.6 6

Diagnostic Procedures

2008 Chevrolet Chevy Express G2500, Van Cargo, 6.6 6SECTION Diagnostic Procedures
WARNING: This page is about a different car, the 2003 Pontiac Vibe. However, it is still accessible from the selected car via links, so may be relevant.
  1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, perform diagnostic system check - engine controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS  under SELF-DIAGNOSTIC SYSTEM.
  2. Start and idle engine until engine reaches normal operating temperature. Using scan tool, store freeze frame and DTC information. Turn ignition OFF and wait 30 seconds. Turn ignition switch to RUN position, engine OFF. Use scan tool to clear DTCs. Start and idle engine. Wait 60 seconds, then check for stored DTCs. Does this DTC reset? If yes, go to step  4. If no, go to next step.
  3. Is there an idle quality concern? If yes, go to ROUGH, UNSTABLE, OR INCORRECT IDLE AND STALLING under SYMPTOM DIAGNOSIS in TROUBLE SHOOTING - NO CODES - 1.8L VIBE article. If no, go to DIAGNOSTIC AIDS .
  4. Turn ignition OFF. Disconnect IAC valve 3-pin harness connector. Turn ignition switch to RUN position, engine OFF. Using test light connected to ground, probe terminal No. 2 of the IAC valve harness connector. Does test light illuminate? If yes, go to next step. If no, go to step  8.
  5. Using test light connected to battery voltage, probe IAC valve harness connector terminal No. 3. Does test light illuminate? If yes, go to next step. If no, go to step  8.
  6. Turn ignition OFF. Jump terminal No. 2 of IAC valve connector on the harness side to terminal No. 2 of the IAC valve with a fused jumper wire. Jump terminal No. 3 of IAC valve connector on harness side to terminal No. 3 of the IAC valve with a fused jumper wire. Connect a fused jumper wire to terminal No. 1 of IAC valve (component side). Insulate terminal No. 1 jumper from contact to ground. Start and idle the engine. With engine idling, repeatedly touch the terminal No. 1 jumper to battery ground with a rapid ON-OFF motion. Does engine speed increase as terminal No. 1 jumper is rapidly grounded ON and OFF? If yes, go to next step. If no, go to step  10.
  7. Turn ignition OFF. Remove all jumpers. Disconnect PCM White 34-pin harness connector (containing IAC valve open control circuit). Check IAC valve open control circuit, terminal No. 1, for a grounded, open, or short to voltage circuit. Repair circuit as necessary. Was a circuit repair made? If yes, go to step  12. If no, go to step  11.
  8. Locate cause of no power to IAC valve connector. Refer to TEST DESCRIPTION . Repair as necessary. After repair, go to step  12.
  9. Repair open IAC valve ground circuit. After repair, go to step  12.
    10. NOTE: IAC valve seals the coolant passage of the throttle body.
  10. Replace IAC valve. After repair, go to step  12.
  11. Replace PCM. After repair, go to next step.
  12. Use scan tool to clear DTCs. Turn ignition OFF for 30 seconds. Start engine. Operate vehicle within CONDITIONS FOR RUNNING DTC  as specified. Are any DTCs displayed on scan tool? If yes, go to next step. If no, go to step  2.
  13. Using scan tool, observe stored information, CAPTURE INFO. Does scan tool display any DTCs that have not been diagnosed? If yes. See DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no other DTCs are displayed, system is okay at this time.
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.