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Home >> Mitsubishi >> 2000 >> Montero >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Self-Diagnostics >> Diagnostic Tests >> DTC P0505: Idle Control System Malfunction >> Diagnostic Procedure
July 1: So it begins. Don't worry, this is not in the correct legal jurisdiction!

Diagnostic Procedure

  1. If using scan tool, go to next step. If using lab scope, go to step  3 .
  2. Using scan tool, read data list item No. 45 (idle air control position sensor step). See IAC POSITION SENSOR STEP SPECIFICATIONS  table. If scan tool does not read as specified, go to step  7 . If readings are as specified, problem is intermittent. For trouble shooting, see INTERMITTENT DTCS  under CIRCUIT TESTS.
    IAC POSITION SENSOR STEP SPECIFICATIONS

    A/C Switch Position (1) Step Value
    Off 2-25
    Off To On Increase By 10-70
    (2) Increase By 5-50
    (1) Check with engine coolant temperature 185-203°F (85-95°C), lights and accessories off, transmission in Park, except where noted, and engine at idle.
    (2) A/C off. Apply brake. Move gear selector lever to Drive.
    3. NOTE: Check waveform when idle speed increases when A/C is turned on. Waveform display lasts less than one second.
    Fig 1: Identifying Normal IAC Motor Waveform
    G97J06407Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
  3. Install special Test Harness (MD998463) between IAC motor connector component side and harness side, or backprobe at connector. Using lab scope, connect pick-up in sequence to IAC motor connector terminals No. 1 (Red clip), No. 3 (Green clip), No. 4 (Black clip) and No. 6 (Yellow clip), or ECM terminals No. 14, 28, 15 and 29, respectively. Start engine and allow it to idle. Turn A/C on. Compare oscilloscope waveform with known-good waveform. See Fig 1 . Turn engine off. If waveform is not normal, go to next step. If waveform is normal, go to step  9 .
  4. Turn ignition off. Remove MFI relay. Disconnect IAC motor 6-pin connector. Check continuity between IAC motor connector terminal No. 2 and MFI relay connector terminal No. 1. If continuity does not exist, repair wiring as necessary. If continuity exists, go to next step.
  5. Check continuity between IAC motor connector terminal No. 5 and MFI relay connector terminal No. 1. If continuity does not exist, repair wiring as necessary. If continuity exists, go to next step.
  6. Disconnect ECM 35-pin connector C-148. Ground specified ECM connector terminal and check continuity between ground and specified IAC motor connector terminal. See ECM-TO-IAC MOTOR HARNESS CIRCUIT IDENTIFICATION  table. If continuity does not exist, repair wiring as necessary, then go to step  10 . If continuity exists, go to next step.
    ECM-TO-IAC MOTOR HARNESS CIRCUIT IDENTIFICATION

    ECM Terminal No. IAC Motor Terminal No.
    14 1
    15 4
    28 3
    29 6
  7. Check resistance between IAC connector terminal No. 2 (White clip) and either terminal No. 1 (Red clip) or No. 3 (Blue clip), and between IAC connector terminals No. 5 (Green clip) and either terminal No. 4 (Black clip) or No. 6 (Yellow clip). Resistance should be 28-33 ohms at 68°F (20°C). If resistance is as specified, go to next step. If resistance is not as specified, replace IAC motor, then go to step  10 .
  8. Remove throttle body. Remove IAC motor. Connect positive terminal of Test Harness (MD998463) 6-volt DC power supply to IAC motor connector (component side) terminals No. 2 (White clip) and No. 5 (Green clip). Check for IAC motor vibration as negative terminals of 6-volt power supply are connected to each of following combinations of IAC motor connector terminals in sequence:
    • Terminals No. 1 (Red clip) and No. 4 (Black clip).
    • Terminals No. 3 (Blue clip) and No. 4 (Black clip).
    • Terminals No. 3 (Blue clip) and No. 6 (Yellow clip).
    • Terminals No. 1 (Red clip) and No. 6 (Yellow clip).
    • Terminals No. 1 (Red clip) and No. 4 (Black clip).
    • Terminals No. 1 (Red clip) and No. 4 (Black clip).
    • Terminals No. 1 (Red clip) and No. 6 (Yellow clip).
    • Terminals No. 3 (Blue clip) and No. 6 (Yellow clip).
    • Terminals No. 3 (Blue clip) and No. 4 (Black clip).
    • Terminals No. 1 (Red clip) and No. 4 (Black clip).
    Vibration should be present at voltage application to each terminal combination. If IAC motor performs as specified, check for throttle valve deposits. Reinstall throttle valve and IAC motor, then go to next step. If IAC motor does not perform as specified, replace IAC motor, then go to step  10 .
  9. Check adjustment of standard idling speed. Check for throttle valve deposits, intake system air leak, basic ignition and fuel systems, and engine condition. If problem exists, repair as necessary, then go to next step. If problem does not exist, problem is intermittent. See INTERMITTENT DTCS  under CIRCUIT TESTS.
  10. Connect all disconnected components. Using scan tool, clear DTCs. Test drive vehicle following other monitor drive cycle pattern. See OBD-II DRIVE CYCLES under VERIFYING REPAIRS in SELF-DIAGNOSTICS - INTRODUCTION article. Check for DTCs. Confirm DTC does not reset. See VERIFYING REPAIRS in SELF-DIAGNOSTICS - INTRODUCTION article.
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