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DTC codes / Subaru codes / P1510

P1510 · SubaruIdle Air Control Solenoid Signal 1 Circuit Low Input

P1510 on a Subaru means the engine control module (ECM) has detected an abnormally low voltage on the signal circuit for the idle air control (IAC) solenoid, specifically signal 1. The ECM expects a certain voltage range from the IAC valve's position feedback or command circuit, and a low input tells it the circuit is shorted to ground or the solenoid has failed.

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

Symptoms you may notice

  • Check engine light illuminated on the dashboard
  • Rough or erratic idle, sometimes stalling when coming to a stop
  • Idle speed too low or fluctuating up and down
  • Engine may hesitate or stumble on acceleration from idle
  • Often no symptoms besides the warning light, especially if the fault is intermittent

Common causes, most likely first

  1. Faulty idle air control solenoid (internal short or open winding)
  2. Damaged or corroded wiring harness to the IAC valve (chafed wire shorted to ground)
  3. Poor electrical connection at the IAC valve connector (loose pins, corrosion, water intrusion)
  4. Failed engine control module (ECM) driver circuit for the IAC solenoid
  5. Carbon buildup or mechanical binding inside the IAC valve causing abnormal current draw
  6. Aftermarket or incorrect IAC valve installed that does not match Subaru specifications

How to diagnose and fix it

  1. Connect a scan tool and verify P1510 is current; check for other codes and freeze-frame data
  2. Inspect the IAC valve connector and wiring for corrosion, loose pins, or chafed insulation
  3. Measure resistance across the IAC solenoid terminals and compare to Subaru service specifications
  4. Backprobe the signal circuit at the ECM and check for a short to ground with a multimeter
  5. Remove and clean the IAC valve passages and throttle body of carbon deposits
  6. If resistance or circuit tests fail, replace the IAC valve with an OEM-quality unit and clear codes
  7. If the circuit is intact and the valve tests good, diagnose the ECM driver circuit or replace the ECM as a last resort

Before you replace the idle air control valve

  • A low input code often comes from a chafed wire grounding against the intake manifold rather than a failed solenoid, so always inspect the harness before condemning the valve.
  • Carbon buildup inside the IAC valve can cause the solenoid to draw excessive current and set a low input code even though the valve still moves.
  • Aftermarket IAC valves for Subaru engines frequently have different resistance values and can set P1510 immediately after installation.
  • The ECM driver for the IAC circuit can fail and mimic a bad valve, so a resistance test at the ECM connector is the only way to rule it out.
  • P1510 can be intermittent and only set during cold starts or after the engine reaches operating temperature, so a wiggle test of the harness while monitoring live data is essential.

Can I keep driving with P1510?

You can usually drive the car to a repair shop, but avoid prolonged idling in traffic and be ready for the engine to stall when you lift off the throttle. If the idle is very unstable or the engine stalls frequently, stop driving and have it towed to prevent an accident.

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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