Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
1995 Subaru Legacy Outback, StandardFACTORY OEM SERVICE PROCEDURE
DTC P0505 (ISC) - Idle Control System Malfunction
- Turn ignition to ON. Start engine and run at idle. Check intake manifold, idle air control solenoid valve and throttle body for loose installation and gaskets for cracks. Check by-pass hoses for loose connections and cracks. Check vacuum hoses for disconnections and cracks.
- Turn ignition to ON. Measure voltage between ECM connector B84, terminals No. 11 and 12. If voltage is 3 volts or more, go to step 4). If voltage is less than 3 volts, go to step 3). Turn ignition to OFF. Disconnect connector from idle air control solenoid valve. Turn ignition to ON. Measure voltage between ECM connector B84, terminals No. 11 and 12. If there is 10 volts or more, repair short circuit in harness and replace ECM. If voltage is less than 10 volts, check for poor contact in ECM connector. If contact is poor, repair contact in ECM connector. If contact is okay, go to next step.
- Turn ignition to OFF. Measure resistance between solenoid valve connector E7, terminals No. 1 and 2, and terminal No. 2 and 3. If resistance is 20 ohms or more, replace idle air control solenoid valve. If resistance is 5 ohms or less, replace idle air solenoid valve and ECM. If resistance is 5-20 ohms, remove idle air solenoid. Connect battery voltage across terminals No. 1 and 2 of idle air control solenoid valve. If valve does not open fully, clean idle air solenoid valve. If valve opens fully, connect battery voltage across terminals No. 2 and 3 of idle air control solenoid valve. If valve closes fully, go to next step. If valve does not close fully, clean idle air control solenoid valve.
- Turn ignition to OFF. Disconnect connector from idle air control solenoid valve. Turn ignition to ON. Measure voltage between idle air control solenoid valve connector E7, terminal No. 2 and ground. If voltage is 10 volts or more, go to next step. If voltage is less than 10 volts, repair open circuit in harness between idle air control solenoid valve connector and ECM connector.
- Turn ignition to OFF. Disconnect connector from ECM. Measure resistance of harness connector between ECM connector B84, terminal No.11 and idle air solenoid connector E7, terminal No. 1, and ECM connector B84, terminal No. 12 and idle air solenoid connector E7, terminal No. 3. If resistance is more than 10 ohms, repair open circuit of harness between ECM connector and idle air control solenoid valve connector. If resistance is more than 10 ohms, measure resistance between ECM connectors No. 11 and ground, and No. 12 and ground. If resistance is 1 M/ohm or more, confirm good condition in connectors of idle air control solenoid valve circuit. If resistance is less than 1 M/ohm, repair short in harness between ECM connector and idle air control solenoid valve connector.
Factory Service Tools
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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.