P2409 Fuel Cap Sensor/Switch Circuit Range/Performance

P2409 is the plausibility code of the fuel cap sensor family: the circuit is electrically sound, but the reported cap state does not fit other information. A switch that never changes over a refuelling event, or one that reports closed while the leak test sees a gross leak, would be typical cases. No manufacturer publicly documents P2409. The closest documented logic is pressure-based: Ford's OBD summary flags a loose or missing cap (P0457) when the tank fails to reach -8 inH2O of vacuum within 30 s after refuelling, and clears it once purge vacuum is back above that level. CARB requires input components to be checked for rationality as well as circuit faults. P2408 is the generic circuit fault, P2410/P2411 the low/high signal codes, P2412 a dropout.

Likely causes

Symptoms

• Check engine light or fuel cap message although the cap is tight
• EVAP test results may be rejected

Repair estimate

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

Related codes

References: law.cornell.edu, newtonnet.co.uk.