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Home >> Chevrolet >> 2002 >> Prizm Base, 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 diagnostic system check - engine controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS  under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check, go to next step.
  2. Start and idle the engine until the engine reaches a normal operating temperature. Using a scan tool, store the Freeze Frame and DTC information. Turn OFF the ignition and wait 30 seconds. Turn ON ignition, with engine OFF. Perform the scan tool Clear DTC Information function. Start and idle the engine. Wait 60 seconds, then check for stored DTCs. Does this DTC reset? If yes, go to step  4 . If no, 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 OFF the ignition. Disconnect the IAC valve electrical connector. Turn ON ignition, with engine OFF. Using a test light connected to ground, probe terminal No. 2 of IAC valve connector on the harness side. Does the test light illuminate? If yes, go to next step. If no, go to step  8 .
  5. Using a test light connected to B+, probe terminal No. 3 of the IAC valve connector. Does the test light illuminate? If yes, go to next step. If no, go to step  9 .
  6. Turn OFF ignition. Using a fused jumper wire, jumper IAC valve harness connector terminal No. 2 to IAC valve terminal No. 2. Jumper IAC valve harness connector terminal No. 3 to IAC valve terminal No. 3. Connect a jumper wire to IAC valve terminal No. 1. Start and idle engine. With engine idling, repeatedly touch the IAC valve terminal No. 1 jumper to battery ground with a rapid ON-OFF motion. Does engine speed increase as terminal No. 1 jumper is rapidly grounded ON and OFF? If yes, go to next step. If no, go to step  10 .
  7. Turn OFF ignition. Remove all jumpers. Disconnect PCM connector containing the IAC valve open control circuit. Check IAC valve terminal No. 1 circuit for grounded, open, or shorted to voltage circuit. Repair circuit as necessary. Was a circuit repair made? If yes, go to step  12 . If no, 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. Repair open IAC valve ground circuit. After repairs, go to step  12 .
    NOTE: The IAC valve seals the coolant passage of the throttle body.
  10. 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. Use scan tool in order to clear DTCs. Turn OFF the ignition for 30 seconds. Start engine. Operate vehicle within the Conditions for Running the DTC. See CONDITIONS FOR RUNNING DTC  . Are any DTCs displayed on scan tool? If yes, go to next step. If no, go to step  2 .
  13. With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? If yes, go to DIAGNOSTIC TROUBLE CODE DEFINITIONS  . If no, system is okay.
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