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Home >> Chevrolet >> 2000 >> Prizm LSi, Standard >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls Self-Diagnostics - 1.8L >> Diagnostic Tests >> DTC P0505: Idle Control System >> Diagnostic Procedures

Diagnostic Procedures

  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 and warm engine to 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 resets, go to step  4 . If DTC does not reset, go to next step.
  3. If idle quality is poor, perform SYMPTOM DIAGNOSIS. See appropriate TROUBLE SHOOTING - NO CODES article. If idle quality is okay, see DIAGNOSTIC AIDS  .
  4. Turn ignition off. Disconnect IAC valve harness 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 harness connector. Check for grounded or open/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. After replacing IAC valve, go to step  12 .
  11. Replace PCM. Program replacement 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 affected DTC(s).
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