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DTC codes / Subaru codes / P1517

P1517 · SubaruIdle Air Control Solenoid Signal 4 Circuit High Input

P1517 on a Subaru indicates that the engine control module (ECM) has detected an abnormally high voltage on the signal circuit for the idle air control (IAC) solenoid's fourth output channel. The ECM expects a specific voltage range when commanding the solenoid, and a high reading tells it the circuit is open, shorted to voltage, or the solenoid winding is faulty.

SystemPowertrain
Code typeSubaru specific
SeverityMedium
Fix difficultyIntermediate
AreaVehicle speed, idle control and auxiliary inputs

Symptoms you may notice

  • Check engine light illuminated, often with no other noticeable symptoms
  • Rough or erratic idle, sometimes stalling when coming to a stop
  • Idle speed stuck too high or too low, especially when cold
  • Hesitation or stumble on acceleration from a stop
  • Occasional surging during idle or when the air conditioning engages

Common causes, most likely first

  1. Open or damaged wire in the IAC solenoid signal circuit (channel 4)
  2. Corroded or loose electrical connector at the IAC solenoid or ECM
  3. Failed IAC solenoid winding or internal short
  4. Short to voltage on the signal wire from chafing or moisture intrusion
  5. Faulty ECM driver for the IAC circuit (rare but possible)
  6. Carbon buildup or mechanical binding in the IAC valve passages causing the solenoid to overheat and fail

How to diagnose and fix it

  1. Inspect the IAC solenoid connector and wiring for corrosion, looseness, or chafing; clean and secure as needed
  2. Measure resistance across the IAC solenoid terminals and compare to specification; replace the solenoid if out of range
  3. Backprobe the signal wire at the ECM and check for a short to voltage with the key on and engine off
  4. Check continuity and resistance of the signal wire from the IAC connector to the ECM; repair any open or high-resistance section
  5. Clean the IAC valve passages and throttle body to eliminate carbon-induced binding that can stress the solenoid
  6. Clear the code and perform an idle relearn procedure if required, then verify the fault does not return during a road test
  7. If all wiring and the solenoid test good, substitute a known-good ECM to rule out a failed driver circuit

What a high IAC signal really tells you

  • A high voltage reading on the IAC signal circuit often points to an open winding inside the solenoid rather than a wiring problem, so resistance testing the solenoid is the quickest first step.
  • Subaru IAC solenoids are sensitive to carbon buildup in the valve passages; a sticking valve can cause the solenoid to draw excessive current and eventually fail, setting this code.
  • The ECM may set P1517 intermittently if the connector pins are loose but not fully disconnected, so wiggle-testing the harness while watching live data can reveal the fault.
  • This code does not always mean the IAC solenoid itself is bad; a short to voltage on the signal wire from a nearby harness rub can produce the same high-input reading.
  • After replacing the IAC solenoid, some Subaru models require an idle relearn or ECM reset to prevent the code from reappearing immediately.

Can I keep driving with P1517?

You can usually drive the car with this code, but expect a rough or erratic idle that may cause stalling at low speeds. Avoid prolonged idling and have the fault diagnosed soon to prevent drivability issues or further damage to the IAC system.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for Subaru vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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