The P0455 trouble code means your vehicle’s computer has detected a large leak in the evaporative emission control (EVAP) system. This usually points to a problem that allows fuel vapors to escape, such as a loose or faulty gas cap or a damaged EVAP component.
Diagnostic trouble code (DTC) P0455 stands for “Evaporative Emission Control System (EVAP) Large Leak Detected.” The engine control module (ECM) sets this code when it determines that the EVAP system cannot maintain the required vacuum or pressure level.
This code has been reported on various vehicles, including Chevrolet (notably Silverado models), Dodge, Ford, Jeep, and Nissan. Code definitions and detection logic may vary slightly by manufacturer, so always consult the appropriate repair manual for your vehicle.
On certain Chevrolet models, such as a 2010 Chevrolet Silverado 1500 5.3L V8, the code sets when the EVAP system cannot achieve or maintain a calibrated vacuum level within a specified time. Conditions for running the test may include:
The test typically runs once per cold start when these conditions are met.
The EVAP system prevents fuel vapors from escaping into the atmosphere. These vapors contribute to pollution and smog formation and contain chemicals that are harmful to humans and wildlife.
The system captures, stores, and later purges fuel vapors back into the engine to be burned. Key EVAP components include:
When the engine is off, vapors are stored in the charcoal canister. When the engine is running and conditions are met, the purge valve opens to route vapors into the intake manifold. During system self-tests, the ECM closes the purge and vent valves and monitors pressure changes to detect leaks.
The ECM performs leak tests either while driving or after the engine is turned off. It seals the system and monitors for vacuum loss or pressure changes. If a large leak is detected, the ECM stores code P0455. Smaller leaks are typically stored as code P0456.
Drivers with a P0455 code may notice:
In many cases, the Check Engine Light may be the only noticeable symptom.
Possible causes of the P0455 code include:
A faulty or improperly sealed gas cap is the most common cause.
P0455 is generally not considered a severe code in terms of immediate drivability. However, it increases harmful emissions and may lead to reduced fuel economy. Fuel vapors can escape continuously, even when the vehicle is parked, which contributes to environmental pollution.
Addressing the issue early can help prevent additional EVAP-related problems and potential emissions test failures.
Start with the simplest and most common checks before moving to more complex testing.
Most DIYers do not have access to specialized EVAP testing equipment, so professional diagnosis may be required if basic checks do not resolve the issue.
Disclaimer: Due to the wide variability in vehicle makes and models, the following information is not a complete or definitive repair guide. It is intended to provide general direction for common fixes.
After repairs are made:
Yes, you can drive with this code present, but the vehicle will produce excess emissions due to fuel vapor leaks. This can contribute to pollution and may slightly affect fuel economy.
Repair costs depend on the cause. A replacement gas cap typically costs under $25, while EVAP system component repairs can reach several hundred dollars in parts and labor.
No. P0455 indicates a large EVAP system leak, while P0456 indicates a small leak. Both relate to vapor containment issues but differ in leak severity.
Yes. Vehicles generally must have no active emission-related trouble codes to pass emissions testing.
The code does not clear automatically. You must use a scan tool to erase it and allow the system to retest.
Yes. A faulty sensor can send incorrect readings that make the ECM believe there is a large leak.
In most cases, it does not significantly affect performance. However, minor drivability issues such as rough starts or stalling can occur in rare situations.
Yes. Some vehicles will not run EVAP tests if the fuel level is too high or too low, which can delay code detection.
If tightening or replacing the gas cap does not resolve the issue and you cannot locate visible damage, professional diagnosis is recommended. Specialized EVAP testing equipment is often required to accurately locate large leaks and faulty components.
Resolving the P0455 code promptly helps reduce emissions, prevents potential fuel economy loss, and ensures the EVAP system continues to function as intended.
Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.