P0440: EVAP System

The evaporative emission (EVAP) system stores fuel vapour from the tank in a charcoal canister; a purge valve lets the engine draw it off, and a vent valve opens the canister to fresh air. P0440 is the general code for a fault in this system without further narrowing down – leak, purge flow or component. Today most makers use the specific codes instead (P0441 ff, P0455–P0457, P0496); the GM and Ford tables of 2006–2023 do not contain P0440. It appears in VW code lists and in an FCA bulletin for the Alfa Romeo 2.0, fixed by software, where FCA calls it incorrect flow. What sets it is therefore manufacturer-specific; CARB requires purge flow and leaks to be monitored.

Symptoms

• Check engine light on
• Possibly slight fuel smell
• Readiness or emission inspection not passed
• No change in driving

Most likely causes

• Fuel cap leaking, loose or wrong
• Purge valve leaking or sticking
• Leaking or cracked EVAP hoses, canister or vent valve
• Engine module software

What to check, in order

Start with the simplest. You can tick off each step.

1. Start with the fuel cap: tighten it fully and check its seal
2. Inspect the hoses and connections around the tank and the charcoal canister
3. Use the scanner to test the purge and vent solenoid valves
4. Run a smoke test to find small leaks

Good to know

• Repair difficulty: medium
• It affects emissions.

What each character of P0440 means

• P: Powertrain: engine and transmission
• 0: Generic code: same on every make
• 4: Emissions
• 40: Specific fault in that system

Frequently asked questions

Can I keep driving with code P0440?

Yes, you can keep driving: it does not usually affect how the car runs. If you smell gasoline inside or around the car, find the source before continuing and do not smoke nearby.

What causes code P0440?

The most common causes are: fuel cap leaking, loose or wrong; purge valve leaking or sticking; leaking or cracked EVAP hoses, canister or vent valve.

Related codes

• P0441EVAP System Incorrect Purge Flow
• P0442EVAP System Leak Detected (small leak)
• P0455EVAP System Leak Detected - Large Leak
• P0456EVAP System Leak Detected (very small leak)
• P0457EVAP System Leak Detected (fuel cap loose/off)
• P0443EVAP System Purge Control Valve A Circuit

Sources

• law.cornell.edu: 13 CCR 1968.2
• static.nhtsa.gov: SB 10053936 1988
• static.nhtsa.gov: MC 10216318 9999
• static.nhtsa.gov: MC 10170388 9999

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.