Possible causes

– Missing or loose fuel cap
– Incorrect fuel filler cap used
– Fuel filler cap remains open or fails to close
– Foreign matter caught in fuel filler cap
– Evaporative Emission (EVAP) canister or fuel tank leaks
– Evaporative Emission (EVAP) system hose leaking
– Fuel tank leaking

When is the code detected?

Malfunction is detected when EVAP control system has detected a very small leak.

Symptoms

– Engine Light ON (or Service Engine Soon Warning Light)
– Possible a noticeable fuel odor caused by the release of fuel vapors

P0456 JEEP Description

The Evaporative emissions system is design to prevent the escape of fuel vapors from the fuel system. Leaks in the system, ca allow vapors to escape into the atmosphere. The leak detection system tests for EVAP system leaks and blockage.
During the self-diagnostics, the Powertrain Control Module (PCM) first checks the Leak Detection Pump (LDP) for electrical and mechanical faults. If the first checks pass, the PCM then uses the LDP to seal the vent valve and pump air into the system to pressurize it. If a leak is present, the PCM will continue pumping the LDP to replace the air that leaks out. The PCM determines the size of the leak based on how fast/long it must pump the LDP as it tries to maintain pressure in the system.

JEEP Technical Service Bulletins for P0456 code