August 14, 2016

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.

Causes

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

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