P0440
EVAP System.
- Generic
- Powertrain
- Generic code
- Low severity
How this code is built
- P
- SystemPowertrain
- 0
- Defined bySAE, the same on every car
- 4
- AreaAuxiliary emission controls
- 40
- FaultThe specific fault in that area
What it means
P0440 is the generic code for a fault in the evaporative emission (EVAP) control system. The EVAP system traps fuel vapour from the tank and feeds it to the engine to be burned. The control unit sets this code when a leak or flow test fails, or when the system cannot hold or draw the expected vacuum or pressure. The code does not say where the fault is, so it needs tracing.
Symptoms
- Malfunction indicator lamp on, often with no other symptom
- Smell of fuel vapour near the car or fuel filler
- Fuel cap warning message on some models
- Slightly harder starting or rough idle just after refuelling if the purge valve is stuck open
- Failed emissions test at inspection
Possible causes
- Fuel filler cap missing, loose, cracked or with a worn seallikely
- Cracked, split or disconnected EVAP hose or pipe, or a poor quick-release connectorlikely
- Purge valve stuck open or leaking, or with a faulty electrical connectionlikely
- Vent valve stuck open or closed, or blocked vent linepossible
- Damaged or saturated carbon canisterpossible
- Damaged fuel filler neck, or leaking fuel tank seal or tank sender gasketpossible
- Faulty fuel tank pressure sensor or its wiringrare
How to diagnose
- Read the stored codes and freeze frame data, and note whether other EVAP or fuel trim codes are present
- Check the fuel cap is fitted, tightens properly and has an undamaged seal; check the filler neck sealing face for damage
- Visually inspect all accessible EVAP hoses, pipes, connectors and electrical plugs for cracks, splits, perishing or disconnection
- Check the purge valve and vent valve wiring, connectors and operation using the manufacturer's procedure, as location and test method vary by model
- Command the valves with a diagnostic scan tool where supported, and listen for clicking and check they open and close as expected
- Check the tank pressure sensor reading against ambient pressure with the system vented
- Carry out a smoke test or a controlled pressure test of the EVAP system, following the manufacturer's limits, to find the leak
- Inspect the carbon canister and tank sender seal for damage or fuel contamination
How to fix
- Replace the fuel cap with a correct one if it is missing, damaged or not sealing
- Repair or replace leaking or damaged EVAP hoses, pipes and connectors
- Replace a faulty purge valve or vent valve, and repair any wiring or connector fault
- Replace a damaged filler neck, canister or tank sender seal as found
- Replace a faulty tank pressure sensor, then clear the code and confirm the EVAP monitor runs and passes
Can I keep driving?
Low severity
The car is normally safe to drive, as this is mainly an emissions fault. Book it in soon, and have a strong fuel smell or visible fuel leak checked straight away.
Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.