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Home >> Chevrolet >> 1999 >> Metro Base, 2D Hatchback >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Tests W/Codes >> Diagnostic Tests >> DTC P0505: Idle Control System (1.3L) >> Diagnosis & Repair

Diagnosis & Repair

  1. Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK  under SELF-DIAGNOSTIC SYSTEM. After performing OBD system check, go to next step.
  2. Connect scan tool to DLC. Start engine and allow it to reach normal operating temperature. Turn off all electrical accessories. Using scan tool, monitor IAC duty cycle parameter. If scan tool indicates IAC duty cycle is 8-25 percent, go to DIAGNOSTIC AIDS  . Check for an intermittent problem. See appropriate TROUBLE SHOOTING - NO CODES article. If scan tool does not indicate IAC duty cycle is 8-25 percent, go to next step.
  3. Check for vacuum leaks, incorrectly routed vacuum lines and hoses, split or damaged vacuum lines and hoses, blocked inlet air ducts and passages, and plugged air filter element. Repair as necessary. After repairs, go to step  14 . If no problem is found, go to next step.
  4. Disconnect IAC valve electrical connector. Turn ignition on, with engine off. Using test light connected to ground, probe IAC valve connector (harness side) IAC valve battery voltage circuit. See WIRING DIAGRAMS article. If test light illuminates, go to next step. If test light does not illuminate, go to step  6 .
  5. Using DVOM, probe IAC valve connector (harness side) IAC valve battery voltage circuit. See WIRING DIAGRAMS article. If battery voltage is present, go to step  7 . If battery voltage is not present, go to next step.
  6. Repair open or short in IAC valve battery voltage circuit between IAC valve and main relay located in relay box, in left side of engine compartment. After repairs, go to step  14 .
  7. Using test light connected to battery voltage, probe IAC valve connector (harness side) IAC valve ground circuit. See WIRING DIAGRAMS article. If test light illuminates, go to step  9 . If test light does not illuminate, go to next step.
  8. Repair open in IAC valve ground circuit between IAC valve and ground connection. After repairs, go to step  14 .
  9. Turn ignition off. Connect IAC valve electrical connector to IAC valve. Disconnect PCM 22-pin connector. Back out PCM 22-pin connector IAC valve control circuit terminal. Reconnect PCM connector with IAC valve control circuit wire terminal removed. Turn ignition on, with engine off. Using DVOM, probe PCM 22-pin connector IAC valve control circuit. See WIRING DIAGRAMS article. If battery voltage is present, go to next step. If battery voltage is not present, go to step  11 .
  10. Start engine. Using scan tool, monitor engine speed parameter. Using test light connected to ground, momentarily probe PCM 22-pin connector IAC valve control circuit. See WIRING DIAGRAMS article. If engine speed increases when test light contacts IAC valve control circuit, go to step  13 . If engine speed does not increase when test light contacts IAC valve control circuit, go to step  12 .
  11. Check for an open or short in IAC valve control circuit between IAC valve and PCM. Repair as necessary. After repairs, go to step  14 . If circuit is okay, go to next step.
  12. Replace IAC valve. After repairs, go to step  14 .
  13. Replace PCM. Program PCM using required equipment. After replacing PCM, go to next step.
  14. After repairs, using scan tool, clear DTC information. Road test vehicle within freeze frame conditions that set DTC. Check for DTCs. If no DTCs are stored, repair is complete. If any DTCs are stored, diagnose DTC(s).
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