Error Code P-456 indicates that the Evaporative Emission (EVAP) control system has a very large leak such as fuel filler cap falling off, or that the EVAP control system is not operating properly.

The Powertrain Control Module (PCM) at different times performs various tests on the EVAP system. The OBD II Enhanced EVAP systems are positioned in place to keep fuel tank vapors from venting into the atmosphere, and instead purges them into the engine to be burned.

Regular pressure tests are conducted by the PCM to monitor the sealed system for leaks. The PCM monitors the EVAP system pressure by watching the fuel tank pressure (FTP) sensor. When the sensor indicates a small leak in the EVAP system, this code is set.


This diagnosis detects leaks in the Evaporative Emission System (EVAP) purge line using engine intake manifold vacuum. If pressure does not increase, the Engine Control Module (ECM) will check for leaks in the line between the fuel tank and EVAP canister purge volume control solenoid valve under the following vacuum test condition.

The vacuum cut valve bypass valve is opened to clear the line between the fuel tank and the EVAP canister purge volume control solenoid valve. The EVAP canister vent control valve will then be closed to shut the EVAP purge line off. The EVAP canister purge volume control solenoid valve is opened to depressurize the EVAP purge line using intake manifold vacuum. After this depressurization is implemented, the EVAP canister purge volume control solenoid valve will be closed.

Common Symptoms

There will likely be no noticeable symptoms other than the Malfunction Indicator Lamp (MIL). This is because the EVAP system is a closed system and only controls fuel tank vapors, not engine management.

Possible Causes

Usually this P0456 code is caused by an incorrect or faulty gas cap. Filling the fuel tank with the engine running could conceivably cause this code as well, or if the cap wasn’t properly tightened. Any of the following could also be the cause:

  • A small leak in any of the EVAP hoses or fuel tank hoses
  • A small leak in the purge valve or vent valve
  • The EVAP Canister may be leaking
  • 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

How to Check

P0456 is a small evaporative emissions leak. Since 1970, systems are designed to not vent gasoline fumes into the atmosphere. This code indicates a failure of this system that might pollute the atmosphere. The code is produced after a test of the fuel system is run. The test puts a pressure in the system (positive pressure I guess, but not sure), and detects over time if the system is sealed by checking if the pressure is maintained. A code scanner such as the Scan Gauge II can clear this code, but the key must be in the “accessory” position (engine not running). The test will rerun periodically (about every 2 days) and it will throw the code again, until you fix it.  State emissions tests will not pass a vehicle in this condition.

To check, you can do the following:

  • Loose vacuum hoses that go to the fuel system.
  • Loose gas cap.
  • Crack in the gas tank refill neck.

How to Fix

Having this kind of error is not much to worry about since it is easy to fix.

P0456 is believed to be a vacuum leak (major). all you have to do is with the car off, turn the ignition switch off and on 3 times. The codes will come up in your odometer. Then you can go to google and search for Dodge/Chrysler T&C codes and find out which one it is. The vacuum leak turned out to be a small 1/4 inch hose (90 degree elbow) on the sensing line from the gas tank (located on the driver side under the car). It was cracked on the top and didn’t even show from the bottom, it had to be removed to find the crack. Now check engine light, small vacuum leak.

First, using a scan tool activate the vent solenoid, sealing the system. Then monitor the fuel tank pressure (FTP) sensor. If the system is sealing properly, the number will stay consistent. If is isn’t, the pressure sensor will show that as well. If the system slowly leaks, use a smoke machine and watch for smoke exiting the system at any EVAP component. Any where there is smoke exiting the system, that is the faulty component. Do not pressurize the EVAP system with air pressure. Doing so can damage the purge and vent solenoids in the system.