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DTC P0509: Idle Control System Circuit High Input

  1. Perform basic diagnostic procedure. See BASIC DIAGNOSTIC PROCEDURE  . Check throttle cable play and adjust as necessary. See ON-VEHICLE ADJUSTMENTS article. If throttle cable is properly adjusted, go to next step.
  2. Turn ignition on. Using a DVOM connected to ground, backprobe ECM connector B136 (24-pin connector) terminal No. 10. See Figure . If voltage is more than 10 volts, go to next step. If voltage is not more than 10 volts, go to step  4 .
  3. Turn ignition off. Disconnect IAC solenoid valve connector. Turn ignition on. Using a DVOM connected to ground, measure voltage at ECM connector B136 (24-pin connector) terminal No. 10. If voltage is more than 10 volts, locate and repair short to voltage in wiring between ECM and IAC solenoid valve. After repair, replace ECM. If voltage is not more than 10 volts, replace IAC solenoid valve and ECM.
  4. Using a DVOM connected to ground, measure voltage at ECM connector B136 (24-pin connector) terminal No. 10 while wiggling harness and ECM connector. If voltage changes more than 10 volts while wiggling harness and ECM connector, locate and repair short to voltage in wiring between ECM and IAC solenoid valve. After repair, replace ECM. If voltage is not more than 10 volts while wiggling harness and ECM connector, contact authorized Subaru dealership because probable cause is deterioration of multiple parts. Clear memory and perform verification procedure. See CLEARING DIAGNOSTIC TROUBLE CODES  and VERIFICATION PROCEDURE  .
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