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Home › Mazda › 2003 › B2300 Base, Automatic › Repair and Diagnosis › Engine Performance › System › Engine Controls - Self-Diagnostics › Diagnostic Tests › DTC P1506: Idle Air Control System Malfunction › Diagnostic Procedures

Diagnostic Procedures

  1. If QUICK TEST was not performed, go to QUICK TEST  under SELF-DIAGNOSTIC SYSTEM. If QUICK TEST was performed, go to next step.
  2. DTC P1506: Check For Vacuum Leaks -  With KOER and engine idling, listen for vacuum leaks. Inspect entire air intake system from Mass Airflow/Intake Air Temperature (MAF/IAT) sensor to intake manifold for damage or leaks such as:
    • Inlet tube(s) from air cleaner to throttle body assembly.
    • IAC valve assembly and gasket seal.
    • Intake manifold gasket seal.
    • EGR valve gasket.
    • Vacuum hoses and lines for cracks and proper connections.
    • PCV system integrity.
    Turn ignition off. If any damage is found, repair as necessary. After repair, go to step  7 . If no damage is found, go to next step.
  3. Check EVAP System For A Stuck Open Valve -  Disconnect hoses at EVAP canister purge solenoid. Connect a hand vacuum pump to EVAP canister purge solenoid port "A". See Fig 1 . Apply 16 in. Hg (53 kPa) of vacuum to EVAP canister purge solenoid. Observe vacuum gauge. If vacuum holds for 20 seconds, reconnect all components. Go to next step. If vacuum does not hold for 20 seconds, replace faulty EVAP canister purge solenoid. After repair, go to step  7 .
    Fig 1: Identifying EVAP Canister Purge Vacuum Ports
    G00155558Courtesy of MAZDA MOTORS CORP.
  4. Check EVAP System For A Stuck Open Valve -  With KOER, verify engine is at normal operating temperature. Put transmission in Park or Neutral. Disconnect IAC valve 2-pin harness connector. Observe engine speed. Turn ignition off. If engine speed dropped or engine stalls, go to next step. If engine speed did not drop or engine did not stall, inspect throttle body for damage. If throttle body is okay, replace faulty IAC valve. If throttle body is damaged, repair or replace throttle body assembly. After repair, go to step  7 .
  5. Check IAC Circuit For Short To Ground -  Disconnect scan tool from DLC. Disconnect PCM 104-pin harness connector. Connect Breakout Box (49-UN01-130) to PCM harness connector only. See Figure . Measure resistance of IAC SIG circuit (White/Light Blue wire) between breakout box terminals No. 83 (IAC circuit) and 51, and 103 (PWR GND circuit). See Fig 2 . If resistance reading is more than 10,000 ohms:
    • For fast idle symptom currently present, replace faulty PCM. After repair, go to step  7 .
    • For all others, go to step  6 .
    If resistance reading is 10,000 ohms or less, repair short circuit in White/Light Blue wire between PCM 104-pin harness connector terminal No. 83 and IAC valve harness connector. See appropriate WIRING DIAGRAM under ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS. After repair, go to step  7 .
    Fig 2: Identifying IAC Valve Harness Connector Circuits
    G00155549Courtesy of MAZDA MOTORS CORP.
  6. Check IAC System For Intermittent Open Or Short -  Connect scan tool to DLC. With KOER, using scan tool, select DIAGNOSTIC DATA LINK. Select PCM. Select PID/DATA MONITOR AND RECORD. Access and observe IAC PID and RPM PID. With engine at normal operating temperature, all accessories off and engine idling, IAC duty cycle must be 20-45 percent. Observe PIDs for an indication of a fault while performing the following:
    • Lightly tap on IAC valve assembly and wiggle harness connector to simulate road shock.
    • Grasp vehicle wiring harness closest to IAC valve assembly. Shake and bend a small section of harness from IAC to dash panel, and from dash panel to PCM.

    If IAC or RPM PIDs suddenly change value indicating a fault, isolate fault and repair as necessary. After repair, go to step  7 . If IAC or RPM PIDs do not suddenly change:

    • For idle quality, starting or stalling problems currently present, replace faulty IAC solenoid. After repair, go to step  7 .
    • For all others, go to INTERMITTENT  testing under SYSTEM TESTS.

  7. Verify Trouble Shooting Of DTCs Completed -  Reconnect all electrical connectors. Using scan tool, clear DTC from PCM memory. Perform QUICK TEST  under SELF-DIAGNOSTIC SYSTEM. If same DTC is present, replace faulty PCM and repeat QUICK TEST  under SELF-DIAGNOSTIC SYSTEM. If any other DTC is present, go to applicable procedure for other DTCs. See DIAGNOSTIC TROUBLE CODE DEFINITIONS  . If no DTC is present, trouble shooting is complete.
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