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Home >> Mazda >> 2002 >> Tribute LX, 4WD >> Repair and Diagnosis >> External Pages >> Different car >> Section 69 (Engine Controls - Self-Diagnostics) >> Diagnostic Tests >> DTC P1506: Idle Air Control System - Malfunction >> Diagnostic Procedures

Diagnostic Procedures

WARNING: This page is about a different car, the 2003 Mazda Tribute. However, it is still accessible from the selected car via links, so may be relevant.
  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 -  Start engine. With engine at idle, listen for vacuum leaks. Inspect entire intake air system from Mass Airflow/Intake Air Temperature (MAF/IAT) sensor to intake manifold for damage or leaks such as:
    • Cracked or punctured intake air tube.
    • EGR valve gasket seal.
    • IAC valve assembly or gasket seal.
    • Intake manifold assembly or gasket seal.
    • Loose or cracked IAC air tubes.
    • Loose intake air tube at air cleaner housing or throttle body.
    • PCV valve, connectors and hoses.
    • Vacuum supply connectors and hose.

    Turn ignition off. If no leaks were detected, go to next step. If any leaks were detected, repair or replace components as necessary. After repair, go to step  7.

  3. Check EVAP System For A Stuck Open Valve -  Disconnect hoses at EVAP canister purge valve. Connect hand vacuum pump at fuel vapor port of EVAP canister at EVAP canister purge valve. Apply 16 in. Hg (53 kPa) of vacuum to EVAP canister purge valve. If EVAP canister purge valve holds vacuum for 20 seconds, reconnect all components and go to next step. If EVAP canister purge valve did not hold vacuum for 20 seconds, replace EVAP canister purge valve.
  4. Check EVAP System For A Stuck Open Valve -  Start engine. Bring engine to normal operating temperature. Ensure transaxle is in park or neutral. Disconnect IAC valve 2-pin harness connector. Turn ignition off. If RPM dropped or engine stalled, go to next step. If RPM did not drop, inspect for throttle body damage. If throttle body is okay, replace Idle Air Control (IAC) valve. If throttle body is not okay, repair or replace throttle body. 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 between breakout box terminal No. 83 (IAC) and terminals No. 51 and 103 (PWR GND). If resistance reading is more than 10,000 ohms and fast idle symptom is present, replace PCM. After repair, go to step  7. For all others, go to next step. If resistance reading is not as specified, repair short in IAC SIG circuit (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.
  6. Check IAC System For Intermittent Open Or Short -  Connect scan tool to DLC. Start engine. Using scan tool, select DIAGNOSTIC DATA LINK. Select PCM. Select PID/DATA MONITOR AND RECORD. Access IAC PID and RPM PIDs. With engine at normal operating temperature, accessories off and at idle, IAC duty cycle must be 20-45 percent. Observe PIDs for an indication of a fault while performing following at idle:
    • Lightly tap on IAC valve assembly and wiggle harness connector to simulate road shock.
    • Grasp vehicle 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 in value (indicating a fault), isolate fault and repair as necessary. After repair, go to next step. If IAC or RPM PIDs do not change, for idle, starting or stalling symptoms currently present, replace IAC solenoid. After repair, go to next step. For all other problems, refer to INTERMITTENT  testing under SYSTEM TESTS.

  7. Verify Trouble Shooting Of DTCs Completed -  Reconnect all disconnected connectors. Clear DTCs from PCM memory using scan tool. Perform QUICK TEST  under SELF-DIAGNOSTIC SYSTEM. If same DTC is present, replace faulty PCM. Repeat QUICK TEST  under SELF-DIAGNOSTIC SYSTEM. If same DTC is not present, go to applicable procedure for other DTCs. See DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no DTCs are present, trouble shooting is complete.
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