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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 (1.8L) >> 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. Start engine and allow it to reach normal operating temperature (closed loop) Using scan tool, store freeze frame and DTC information. Turn ignition off and wait 30 seconds. Turn ignition on, with engine off. Using scan tool, clear DTC information. Start and idle engine. Wait 60 seconds, and then check for DTCs. If DTC P0505 resets, go to step  4 . If DTC P0505 does not reset, go to next step.
  3. If idle quality is poor, diagnosis by symptom. See appropriate TROUBLE SHOOTING - NO CODES article. If idle quality is okay, go to DIAGNOSTIC AIDS  . Check for an intermittent problem. See appropriate TROUBLE SHOOTING - NO CODES article.
  4. Turn ignition off. 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  8 .
  5. 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 next step. If test light does not illuminate, go to step  9 .
  6. Turn ignition off. Connect a jumper wire from IAC valve open control circuit terminal of IAC valve connector to IAC valve open control circuit terminal of IAC valve. See WIRING DIAGRAMS article. Connect a second jumper wire from ground circuit terminal of IAC valve connector to ground circuit terminal of IAC valve. Connect a fused jumper wire to battery voltage circuit of IAC valve and insulate jumper from electrical ground contact. Start engine and let idle. With engine idling, repeatedly touch IAC valve battery voltage circuit jumper to battery ground with a rapid on/off motion. If engine speed increases as IAC valve battery voltage circuit is rapidly grounded on and off, go to next step. If engine speed does not increase as specified, go to step  10 .
  7. Turn ignition off. Remove all jumper wires. Disconnect PCM 26-pin connector. Check for a grounded, open or short to voltage in IAC valve open control circuit between IAC valve and PCM. Repair as necessary. After repairs, go to step  12 . If circuit is okay, go to step  11 .
  8. Locate cause of no power to IAC valve connector. Repair as necessary. After repairs, go to step  12 .
  9. Repair open in IAC valve ground circuit between IAC valve and ground connection. Repair as necessary. After repairs, go to step  12 .
  10. IAC valve seals the coolant passage of throttle body. Replace IAC valve. Repair as necessary. After repairs, go to step  12 .
  11. Replace PCM. Program PCM using required equipment. After replacing PCM, go to next step.
  12. 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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