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DTC codes / Subaru codes / P1400

P1400 · SubaruFuel Tank Pressure Control Solenoid Low Input

P1400 on a Subaru means the engine control module (ECM) has detected an abnormally low voltage on the control circuit for the fuel tank pressure control solenoid, which is part of the evaporative emissions (EVAP) system. The ECM expects to see a specific voltage when the solenoid is commanded on or off, and a low input tells it the circuit is likely shorted to ground or the solenoid 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 slight fuel odor around the rear of the vehicle if the EVAP system cannot hold pressure.
  • Rough idle or hesitation in rare cases when the solenoid sticks open and upsets fuel tank pressure.
  • Failed emissions inspection due to the stored trouble code.
  • In some instances, a faint clicking or buzzing from the solenoid area when the key is turned on.

Common causes, most likely first

  1. Faulty fuel tank pressure control solenoid with an internal short to ground.
  2. Damaged or chafed wiring between the solenoid and the ECM, shorting the control wire to ground.
  3. Corroded or loose electrical connector at the solenoid, causing intermittent low voltage.
  4. Water intrusion into the solenoid connector or wiring harness, leading to a short.
  5. ECM internal driver failure, though this is less common than solenoid or wiring faults.

How to diagnose and fix it

  1. Connect a scan tool and verify P1400 is active, then command the solenoid on and off while watching the voltage or listening for a click.
  2. Visually inspect the solenoid connector and wiring for corrosion, chafing, or signs of water intrusion.
  3. Measure resistance across the solenoid terminals and compare to the manufacturer's specification to check for an open or shorted coil.
  4. Disconnect the solenoid and check the control wire for continuity to ground with the key off; a short to ground indicates wiring repair is needed.
  5. If wiring and connector are good, substitute a known-good solenoid and clear the code to see if it returns.
  6. If the code persists after replacing the solenoid, test the ECM control circuit with a lab scope or substitute a known-good ECM.
  7. After repairs, clear codes and perform a drive cycle to confirm the EVAP monitor completes without resetting P1400.

What the low input really means

  • A low input code does not automatically mean the solenoid is dead; a shorted wire or corroded connector can pull the voltage down just as easily.
  • Subaru EVAP systems are sensitive to fuel cap sealing and tank pressure, so a loose or faulty fuel cap can sometimes trigger related codes but not P1400 directly.
  • The fuel tank pressure control solenoid is often confused with the vent solenoid; on many Subaru models they are separate components, and testing the wrong one wastes time.
  • Intermittent P1400 can be caused by a harness rubbed through near the fuel tank, especially on older models where road debris or rust has damaged the loom.
  • Always check for technical service bulletins (TSBs) for the specific Subaru model and year, as some have known connector or solenoid update procedures.

Can I keep driving with P1400?

You can generally continue driving with P1400 because it primarily affects emissions and does not compromise engine safety or performance. Avoid ignoring it long-term, as a persistent EVAP fault can lead to a failed emissions test and may mask other fuel system issues.

Tools that help

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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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