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DTC codes / Subaru codes / P1423

P1423 · SubaruEVAP Vent Control High Input

P1423 on a Subaru means the engine control module (ECM) has detected an abnormally high voltage on the electrical circuit that controls the evaporative emission (EVAP) vent valve, which is usually a solenoid that seals the charcoal canister from the atmosphere. The ECM expects the vent circuit to pull low when commanded, so a high input tells the computer the circuit is open, shorted to power, or the valve itself has failed internally.

SystemPowertrain
Code typeSubaru specific
SeverityLow
Fix difficultyIntermediate
AreaAuxiliary emission controls

Symptoms you may notice

  • Illumination of the check engine light, often with no other noticeable symptoms.
  • A faint fuel odor around the rear of the vehicle if the vent valve sticks open and cannot seal the canister.
  • Slightly rough idle or a stumble after refueling in some cases, because the EVAP system cannot purge correctly.
  • Failed state emissions inspection due to the stored code and incomplete EVAP monitor.
  • In rare instances, a hard start or rough running if the vent valve remains open and allows excessive fuel vapor into the intake.
  • No drivability change at all in many cases, since the fault is purely electrical and does not affect engine operation.

Common causes, most likely first

  1. Failed EVAP vent valve solenoid with an open internal coil, which is the most common cause on Subaru models.
  2. Damaged, corroded, or disconnected wiring or connector at the vent valve, often from road debris or moisture intrusion.
  3. Open circuit in the power or ground side of the vent valve circuit, including a broken wire in the harness near the canister.
  4. Short to voltage on the control wire between the ECM and the vent valve, which can be caused by chafed insulation.
  5. Faulty ECM driver for the vent valve circuit, though this is rare and should only be suspected after all other possibilities are ruled out.
  6. Corroded terminals at the ECM connector, usually from water intrusion, causing high resistance that mimics an open circuit.
  7. Aftermarket alarm or remote start wiring that taps into the EVAP circuit and introduces a high-voltage fault.

How to diagnose and fix it

  1. Connect a scan tool and verify P1423 is current or pending, then command the vent valve on and off while watching the circuit voltage to confirm the fault is electrical.
  2. Visually inspect the vent valve, its connector, and the wiring harness for damage, corrosion, or loose pins, especially around the rear canister area.
  3. Measure resistance across the vent valve solenoid terminals and compare to the manufacturer's specification to check for an open coil.
  4. Check for battery voltage on the power side of the vent valve connector with the key on, and check the ground side for continuity to chassis ground.
  5. Perform a voltage drop test on the control wire between the ECM and the vent valve while commanding the valve on to detect a short to voltage.
  6. If the circuit and valve test good, substitute a known-good vent valve and clear the code to see if it returns before condemning the ECM.
  7. After any repair, clear the codes, run the EVAP monitor to completion, and verify no pending or current P1423 returns.

What Subaru techs check before replacing the vent valve

  • A high input code often sets because the vent valve connector is unplugged or the pins are pushed back, not because the solenoid itself has failed.
  • Subaru vent valves are pulse-width modulated on some models, so a standard test light can give a false pass; use a duty-cycle-capable meter or a scan tool to verify the command signal.
  • Spider webs or mud dauber nests in the vent valve filter can cause the valve to stick and set a high input code on the circuit, even though the electrical tests pass.
  • The ECM may set P1423 intermittently if the vent valve coil resistance drifts with temperature, so a cold resistance check alone can miss a failing solenoid.
  • A weak battery or poor ground can cause the ECM to misread the vent circuit voltage, so always check charging system health before chasing the EVAP wiring.

Can I keep driving with P1423?

You can usually continue driving with P1423 because it does not affect engine performance or safety, but avoid topping off the fuel tank and park away from strong odors until the fault is repaired. Have the code diagnosed soon to prevent a failed emissions test and to avoid potential fuel vapor leaks.

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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