P0440 - General Evaporative Emission System Malfunction

The Technical Definition: The PCM has detected an unspecified malfunction in the EVAP system, meaning fuel vapors are not being contained and routed to the engine properly.

Common Symptoms: The check engine light illuminates, and there may be a faint smell of raw gasoline near the rear of the Jeep.

Typical Fix: Because this is a general code, you start with the cheapest parts: check the gas cap seal and the filler neck for rust. If those are clear, inspect the EVAP canister (located underneath the Jeep, where it is highly susceptible to rock damage on the trail) for cracks.