OBD2 codes.
A code identifies a signal or system that needs to be checked, not a part you should replace.
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P0456Very small leak in the fuel vapour system (EVAP)Urgency low
Evaporative Emission System Leak Detected (Very Small Leak)
The EVAP system collects fuel vapour from the tank in a charcoal filter (the canister) so the engine burns it instead of releasing it into the air. Every so often, the engine computer seals it and checks whether it holds vacuum or pressure. This code means a very small leak, around half a millimetre (0.020 inch).
What the car has detected
With the system sealed, vacuum or pressure drops a little faster than expected: there is a very small leak that usually only a smoke test can find.
The car usually drives normally and it is not dangerous, but fuel vapour escapes and the car may fail the inspection. If you smell a lot of fuel or see a liquid leak, have it checked now.
Symptoms
- Engine warning light on, often with nothing else
- The light comes and goes on its own, because the test needs certain fuel and temperature conditions
- Fuel smell near the tank or at the rear
- Failing the emissions test at the inspection
- Rarely: rough idle or hard starting after refuelling, if the purge valve sticks open
Possible causes
- Fuel cap loose, worn or the wrong type (the most common cause)
- Cracked or loose EVAP hoses or pipes
- Faulty purge valve (the one that lets the vapour into the engine)
- Faulty vent valve
- Leaking charcoal canister, or damaged filler neck or tank
- Faulty fuel tank pressure sensor
Checks for the garage
- Check the fuel cap and the sealing surface of the filler neck
- Read the other codes, pending ones too, and the freeze frame data
- Run a smoke test on the EVAP system to find the leak
- Check hoses and pipes, flexing them with smoke inside
- Test the purge and vent valves with the diagnostic tool
- Check that the tank pressure sensor reads the same as atmospheric pressure
Next step
Check the fuel cap and its seal and close it until it clicks. If the code comes back, ask for a smoke test of the EVAP system.
If the code comes back after replacing or properly tightening the cap, the garage needs a smoke machine to find the leak. Go sooner if you smell a lot of fuel.