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 it 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 testson the EVAP system. OBD II Enhanced EVAP systems are in place to keep fuel tankvapors from venting into the atmosphere, and instead purges them into the engineto be burned.
Regular pressure tests are conducted by the PCM to monitor thesealed system for leaks. The PCM monitors the EVAP system pressure by watchingthe fuel tank pressure (FTP) sensor. When the sensor indicates a small leakin the EVAP system, this code is set.
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 IndicatorLamp (MIL). This is because the EVAP system is a closed system and only controlsfuel tank vapors, not engine management.
Causes
Usually this P0456 code is caused by an incorrect or faulty gas cap. Fillingthe fuel tank with the engine running could conceivable cause this code as wellor if the cap wasn't properly tightened. Any of the following could also bethe 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. Thenmonitor 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 slowlyleaks, use a smoke machine and watch for smoke exiting the system at any EVAPcomponent. 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 thepurge 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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