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Home >> Chevrolet >> 2001 >> Prizm Base, Standard >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls Self-Diagnostics - 1.8L >> Diagnostic Tests >> DTC P0505: Idle Control System >> Diagnostic Procedures
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Diagnostic Procedures

  1. Perform powertrain diagnostic system check. See POWERTRAIN DIAGNOSTIC SYSTEM CHECK  under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic 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 operate engine at idle. 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 harness connector terminal No. 2 (Black wire). See Figure. 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 harness connector terminal No. 3 (Brown wire). 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 between IAC valve harness connector terminals No 2 (Black wire) and No. 3 (Brown wire) and IAC valve terminals No. 2 and 3. See Figure. Connect a fused jumper wire to IAC valve connector terminal No. 1. Start engine and operate at idle. With engine idling, repeatedly touch the fuse jumper wire to battery ground with a rapid on/off motion. If engine speed increases as terminal No. 1 jumper is rapidly grounded on and off, go to next step. If engine speed does not increase, 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 Black/Blue wire between IAC valve and PCM. Repair as necessary. After repairs, go to step  12. If circuit is okay, go to step  11.
  8. Turn ignition off. Locate cause of no power to IAC valve connector. Repair as necessary. After repairs, go to step  12.
  9. Turn ignition off. Repair open in Brown wire between IAC valve and ground connection. Repair as necessary. After repairs, go to step  12.
  10. If IAC valve seals the coolant passage of throttle body. Replace IAC valve. After replacing IAC valve, go to step  12.
  11. Replace PCM. Perform PCM relearn procedure. See POWERTRAIN CONTROL MODULE  under PROGRAMMING. After replacing PCM, go to next step.
  12. Turn ignition on, with engine off. Using scan tool, clear DTC information. Road test vehicle within conditions for running DTC. See CODE ENABLE CRITERIA . Check for DTCs. If no DTCs are stored, repair is complete. If any DTCs are stored, diagnose affected DTCs.
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