Emission control system leak

Article by
Dale Toalston
ASE Certified Technician

OBD-II Trouble Code Technical Description

Evaporative Emissions System - Small leak detected

What does that mean?

This diagnostic trouble code (DTC) is a generic powertrain code, which means that is applies to OBD-II equipped vehicles. Although generic, the specific repair steps may vary depending on make/model.

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

Related evaporative emission trouble codes include P0450, P0451, P0452, P0453, P0454, P0455, P0457, P0458, and P0459.

Potential 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.


Usually this P0456 code is caused by an incorrect or faulty gas cap. Filling the fuel tank with the engine running could conceivable 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

Possible Solutions

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.

Other EVAP DTCs: P0440 - P0441 - P0442 - P0443 - P0444 - P0445 - P0446 - P0447 - P0448 - P0449 - P0452 - P0453 - P0455

Related P0456 DTC Discussions

  • Getting P-0456 code going on and off will not pass emissions testing... Car was smoke tested - No smoke. Changed EGR valve. New MOPAR Gas Cap I should note that the PCM needed to be changed after it was burning out the EGR and 4 Wheel. One other symptom...gas spits out of tank upon fill...
  • P0456 (EVAP Control System Leak Detected Very Small Leak) I have toyota Rav4 2011 V6 limited and since i got it it has that check engine light on and after using the OBD trouple finder it stated that its P0456 error, i read about it on internet and already changed the fuel cab but it didnt work.
  • Hey guys, first off, let me say that I am new, and thanks for taking new people here at the forums. I have a 2005 ford Taurus with 150k miles on it. I just changed the plugs, distributor, and plug wires about 3k miles ago. Well today, I was taking a friend to put in some job applications in the n...
  • I have a 02 gran caravan sport 3.3L the tachometer is higher than usual and it seems like it is not shifting out of 2nd gear. need help before taking it to a transmission shop.
  • I have '08 ram 1500. a P0456 code came on recently. I was just wondering if this problem will cause my gas to burn faster or will it still be normal on gas? if something thats leaking, is it actual fuel thats leaking or vapours or something like that? also, any links to on how I can fix this?? thank...

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