P2409
Fuel Cap Sensor/Switch Circuit Range/Performance
- Severity
- Low
- Driving
- No driving restriction
The fuel cap sensor is producing a valid signal that does not agree with what the module expects - for instance reporting the cap fitted while the leak test finds the tank open to atmosphere. The circuit works; what it says is not consistent with the rest of the evidence.
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.
- Look for EVAP leak codes stored alongside. This code together with a large leak code usually means the cap is genuinely not sealing while its switch insists that it is.
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