P2408
Fuel Cap Sensor/Switch Circuit
- Severity
- Low
- Driving
- No driving restriction
A fault in the fuel cap sensor circuit. This switch tells the module whether the fuel filler cap is fitted and sealed, so it knows not to run a leak test with the tank open to the air. Start with the cap itself rather than the switch: a cap that is loose, cross-threaded or has a perished seal is by far the most common reason for this code.
Possible causes
- CommonFuel cap loose, cross-threaded or not clicked home
- CommonWorn or perished seal on the cap
- CommonFailed cap sensor or switch
- CommonCorroded connector at the filler neck
- PossibleWiring damage in the filler area, where water collects
- PossibleNon-original cap that does not operate the switch correctly
What you might notice
- Check engine light on
- Failed emissions test
- Occasionally a smell of fuel
- Usually nothing else - EVAP faults rarely affect how the car drives
What to check, in order
- Take the fuel cap off and refit it properly, until it clicks. This is the cheapest fix in motoring and it clears a surprising proportion of these codes - do it before anything else.
- Inspect the cap's rubber seal for cracking, hardening or a missing section, and check that the cap is the correct one for the vehicle. Cheap replacements often do not operate the switch.
- Inspect the connector and its wiring before condemning the component. Everything in this system lives under the vehicle in the path of road salt and spray, and a corroded connector produces these codes far more often than a failed part does.
- Check the sensor's signal on live data with the cap on and off. A signal that does not change between the two confirms the switch rather than the cap.
Read this code from your own car
Plug an ELM327 adapter into the OBD-II port under the dashboard. Pin16 reads every stored, pending and permanent code, explains each one like this page does — offline, with no account — and shows what the car recorded when the fault was set.
Where this code sits
P00xxP01xxP02xxP03xxP04xxP05xxP06xxP07xxP08xxP09xxP0AxxP0BxxP0CxxP0DxxP0ExxP0FxxP10xxP11xxP12xxP13xxP14xxP15xxP16xxP17xxP18xxP19xxP1AxxP1BxxP1CxxP1DxxP1ExxP1FxxP20xxP21xxP22xxP23xxP24xxP25xxP26xxP27xxP28xxP29xxP2AxxP2BxxP2CxxP2DxxP2ExxP2FxxP30xxP31xxP32xxP33xxP34xxP35xxP36xxP37xxP38xxP39xxP3AxxP3BxxP3CxxP3DxxP3ExxP3Fxx