2002 Mercury Villager BaseFACTORY OEM SERVICE PROCEDURE

Test KE: Idle Air Control System: Testing

    NOTE: For additional testing information, see DIAGNOSTIC AIDS .

  1. 1) DTC P0505: IAC Valve Resistance
    Disconnect Idle Air Control (IAC) valve harness connector. Using DVOM, measure resistance between IAC valve terminals. If resistance is about 10 ohms at 77°F (25°C), go to next step. If resistance is not about 10 ohms at 77°F (25°C), replace IAC valve.

  2. 2) Check Power Supply To IAC Valve

    Turn ignition on. Using DVOM, measure voltage between negative battery terminal and IGN START/RUN circuit at IAC valve harness connector terminal No. 1 (Blue/Yellow wire). See Figure. If voltage is more than 10 volts, go to next step. If voltage is 10 volts or less, repair open in Blue/Yellow wire. See WIRING DIAGRAMS article.

  3. 3) Check IAC Circuit For Open Or Short To Ground

    Turn ignition off. Disconnect PCM harness connector. Inspect connector for damaged pins and repair if necessary. Using DVOM, measure resistance of IAC circuit (Light Blue wire) between PCM harness connector terminal No. 81 and IAC valve harness connector terminal No. 2. See Figure. Resistance should be less than 5 ohms. Using DVOM, measure resistance of IAC circuit between negative battery terminal and PCM harness connector terminal No. 81. Resistance should be more than 10 k/ohms. If both resistances are as specified, go step  10). If either resistance is not as specified, repair open or short to ground in IAC valve circuit.
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 3) to step 10). No test procedures have been omitted.

  4. 10) Check IAC Valve Operation

    Connect a jumper wire between battery power and IAC valve connector terminal No. 1. Connect another jumper wire between negative battery terminal and IAC valve terminal No. 2. See Figure. If a click is heard when applying battery power to IAC valve, go to next step. If no click is heard when applying battery power to IAC valve, replace IAC valve.

  5. 11) Check Power To ISC Valve

    Start engine and allow it to idle. Turn A/C and blower motor on. Using DVOM, measure voltage between chassis ground and ISC valve harness connector terminal No. 3 (Gray/Red wire). See Figure. If voltage is more than 10 volts, go to next step. If voltage is 10 volts or less, go to Test KM  , step  1).

  6. 12) Check GND Circuit At IAC Valve

    Turn ignition off. Using DVOM, measure resistance between chassis ground and IAC valve harness connector terminal No. 4 (Black wire). If resistance is less than 5 ohms, replace IAC valve. If resistance is 5 ohms or more, repair open in Black wire. See WIRING DIAGRAMS article.
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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.

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