P1401

Code

SUBARU P — Powertrain

Fuel Tank Pressure Control System Performance

Brand: SUBARU

Type: P — Powertrain

Views: UK: 28 EN: 59 RU: 39

AI status

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Page language: EN

Loose or leaking fuel filler cap
Faulty fuel tank pressure sensor (FTPS)
Stuck/open/shorted EVAP vent control valve (canister vent)
Faulty purge valve or purge control circuit
Leaking, cracked, collapsed or disconnected EVAP hoses or charcoal canister damage
Corroded/damaged wiring or poor connector connections to FTPS or EVAP valves

Malfunction Indicator Lamp (MIL) illuminated
Failed emissions/EVAP readiness test
Fuel odor around vehicle or at fill area
Possible difficulty refueling (vapour lock at pump)
Usually no major drivability symptoms, but EVAP-related issues can cause hesitation in rare cases

Read and record DTC(s) and freeze-frame data with a capable scan tool
Check for other EVAP-related codes (P0440, P0441, P0446, etc.)
Verify EVAP system readiness and recent fueling/freeze-frame conditions
Visually inspect filler cap for damage and confirm it is tightened correctly
Inspect EVAP hoses, lines, charcoal canister and vent/purge valve connectors for damage or disconnection
Use an appropriate smoke/leak detector to check for external EVAP leaks

Fuel Tank Pressure Sensor (FTPS) output: typical 0–5.0 V (approx. 2.5 V near atmospheric pressure) — exact scale varies by model
Expected fuel tank pressure near atmospheric at rest; EVAP test may command a measurable vacuum/pressure change (sensor change should be smooth and within manufacturer thresholds)
Purge/vent solenoid command: switched 0–12 V (or PWM) from PCM when actuated
Typical vent/purge solenoid resistance: commonly ~20–40 Ω (varies by part; check Subaru spec)
If FTPS shows no change or erratic voltage while valves are commanded, symptom supports sensor/valve/wiring fault

Confirm P1401 and note freeze-frame data; check for additional EVAP codes and recent vehicle conditions (fuel level, refueling, ambient temp).
Verify simple items: ensure fuel cap is correct, seated and tight; clear code and re-test if cap was loose.
Perform visual inspection of EVAP components: hoses, charcoal canister, vent/purge valves and connectors for damage or disconnections.
With a scan tool, monitor FTPS PID at key ON engine OFF and during commanded EVAP tests; note voltage and pressure behavior at rest and while commanding vent/purge.
Command the vent control valve and purge valve ON/OFF while observing FTPS and confirm tank pressure changes; if no change, suspect vent/purge or leaks.
Measure resistance and supply voltage at vent and purge solenoid connectors; check for open/shorts and proper ground. Verify PCM is commanding correct voltage/PWM.
Perform a smoke/leak test to locate external EVAP leaks (hoses, filler neck, canister). Repair discovered leaks and re-test.
If FTPS output is erratic or out of expected range, bench-test or replace FTPS. If FTPS and EVAP valves test good but system still fails, inspect wiring harness for intermittent faults and connector corrosion.
After repairs, clear codes and run required EVAP monitor/drive cycle to confirm the fault does not return.
If all hardware and wiring check good and symptoms persist, consider PCM software update or replacement as last resort (follow manufacturer guidance).

Faulty or out-of-spec fuel tank pressure sensor
EVAP vent control valve stuck closed or its circuit open/shorted
Large EVAP leak (disconnected hose, damaged canister, loose gas cap) preventing pressure change
Purge valve stuck open or closed or purge control circuit fault
Wiring harness or connector corrosion on FTPS or EVAP solenoids

⚠️ Status

PCM detected fuel tank pressure control system did not perform within expected parameters during EVAP monitor — MIL set.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.5-3 hours

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P1401 — Fuel Tank Pressure Control System Performance