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DTC P0505 (ISC) - IDLE CONTROL SYSTEM MALFUNCTION Subaru Outback BG

Testing & Diagnostics ~575 words
  1. Start and operate engine at idle. Check intake manifold, idle air control solenoid valve and throttle body for loose installation and gaskets for cracks. Check by-pass and vacuum hoses for loose connections and cracks. Repair or replace as necessary. If air intake components are okay, go to next step.
  2. Turn ignition on, with engine off. Using DVOM connected to chassis ground, backprobe ECM harness connector terminals No. 13. See appropriate wiring diagram in «WIRING DIAGRAMS»(ref-26255) article. If voltage reading is 3 volts or greater, go to next step. If voltage reading is less than 3 volts, go to step 8).
  3. Backprobe ECM harness terminal No. 14. If voltage reading is 3 volts or greater, go to next step. If voltage reading is less than 3 volts, go to step 8).
  4. Turn ignition off. Disconnect idle air control solenoid harness connector. Turn ignition on. Backprobe ECM harness connector terminal No. 13. If voltage reading is 10 volts or greater, repair short in harness between ECM and idle air control solenoid. If circuit is okay, replace ECM. If voltage is less than 10 volts, go to next step.
  5. Backprobe ECM harness connector terminal No. 14. If voltage reading is 10 volts or greater, check for short in harness between ECM and idle air control solenoid harness connector. If voltage reading 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.
  6. Turn ignition off. Check resistance between idle air control solenoid harness connector terminals No. 1 and 2, and terminals No. 2 and 3. If resistance is 20 ohms or greater, replace idle air control solenoid. If resistance is 5 ohms or less, replace idle solenoid and ECM. If resistance is greater than 5 ohms, but less than 20 ohms, go to next step.
  7. Remove idle air control solenoid. Connect battery voltage across idle air control solenoid terminals No. 1 and 2. If solenoid valve does not open fully, clean idle air solenoid valve. If solenoid valve opens fully, connect battery voltage across terminals No. 2 and 3. If solenoid valve closes fully, go to next step. If solenoid valve does not close fully, clean idle air control solenoid valve.
  8. Turn ignition off. Disconnect idle air control solenoid valve harness connector. Turn ignition on. Check voltage between idle air control solenoid harness connector terminal No. 2 and chassis ground. If voltage reading is 10 volts or greater, go to next step. If voltage reading is less than 10 volts, repair open in harness between idle air control solenoid harness connector and ECM connector.
  9. Turn ignition off. Disconnect ECM harness connector. Check resistance between ECM harness connector terminal No. 14 and idle air solenoid harness connector terminal No. 1, and ECM harness connector terminal No. 13 and idle air solenoid harness connector terminal No. 3. If resistance is greater than one ohm, repair open in harness between ECM and idle air control solenoid harness connectors. If resistance is one ohm or less, go to next step.
  10. Check resistance between ground ECM harness connector terminals No. 13 and 14. If resistance is 10 ohms or greater, ensure idle air control solenoid valve harness connector terminals are okay. Repair connector terminals as necessary. If resistance is less than 10 ohms, repair short in harness between ECM and idle air control solenoid valve harness connector.

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