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HOMESERVICE MANUALSCHEVROLET2000CHEVY EXPRESS G3500, VAN CARGO EXTENDED, 6.5 FREPAIR AND DIAGNOSIS (SINGLE PAGE)ENGINE PERFORMANCESYSTEMENGINE CONTROL SYSTEM SELF-DIAGNOSTICS - GASOLINE - 4.3L, 5.0L, 5.7L & 7.4LDIAGNOSTIC TESTSDTC P1508: IDLE AIR CONTROL SYSTEM - LOW RPM (5.0L, 5.7L & 7.4L)DIAGNOSTIC PROCEDURES
2000 Chevrolet Chevy Express G3500, Van Cargo Extended, 6.5 F

Diagnostic Procedures

2000 Chevrolet Chevy Express G3500, Van Cargo Extended, 6.5 FSECTION Diagnostic Procedures
  1. Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK . After performing OBD system check, go to next step.
  2. Set parking brakes and block drive wheels. Start engine. Ensure all accessories are off. Using scan tool, command engine speed to 1200 RPM then to 500 RPM. If engine speed corresponds within 100 RPM of commanded speed, see DIAGNOSTIC AIDS . If engine speed does not correspond within 100 RPM of commanded speed, go to next step.
  3. Turn ignition off. Disconnect IAC valve harness connector. Check resistance between IAC valve terminals "A" and "B", and terminals "C" and "D". If resistance is 40-80 ohms, go to next step. If resistance is not 40-80 ohms, go to step  13.
  4. Check resistance between IAC valve terminals "B" and "C", and terminals "A" and "D". If resistance is infinite, go to next step. If resistance is not infinite, go to step  13.
  5. Install Connector Test Adapter (J-35616-A) to IAC valve harness connector. Start engine. Connect test light between ground and connector test adapter terminals. Using scan tool, command RESET IAC on for each circuit tested. If test light flashes on and off at all terminals, go to step  9. If test light does not flash on and off at all terminals, go to next step.
  6. If test light stayed on at any of the terminals during IAC valve reset function, go to step  8. If test light did not stay on during the IAC valve reset function, go to next step.
  7. Check for open or short to ground in IAC valve circuit that did not flash test light. If problem is found, go to step  11. If no problems were found, go to step  10.
  8. Check for short to voltage in IAC valve circuit where test light stayed on. If problem is found, go to step  11. If no problems were found, go to step  10.
  9. Turn ignition off. Remove IAC valve. Check for carbon deposits on valve and throttle body passages. If problem is found, go to step  12. If no problems were found, see DIAGNOSTIC AIDS .
  10. Check for poor connection at VCM. If problem is found, go to next step. If no problems were found, go to step  14.
  11. Repair as necessary. After repairs, go to step  15.
  12. Clean IAC valve and passages. After repairs, go to step  15.
  13. Replace IAC valve. Perform IAC reset procedure if IAC valve is replaced. See appropriate ON-VEHICLE ADJUSTMENTS article. After replacing IAC valve, go to step  15.
  14. Replace VCM. Program replacement VCM using required equipment. After replacing VCM, go to next step.
  15. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter this DTC. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step  2.
  16. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTCs are displayed, go to applicable DTC test.
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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.