A P0456 code means your vehicle’s computer has detected a small leak in the evaporative emission control (EVAP) system. This system is designed to prevent fuel vapors from escaping into the atmosphere, and even a minor leak can trigger the check engine light.
Diagnostic trouble code (DTC) P0456 stands for “Evaporative Emission System (EVAP) Small Leak Detected.” Not all vehicles use this code, so some platforms—such as certain late-model GM vehicles—may never display it.
Your car’s powertrain control module (PCM) sets this code when it determines that a minor leak exists somewhere in the EVAP system. Typically, the PCM must detect the failure during self-testing more than once before the code is stored.
The EVAP system is a network of components that stores and purges fuel vapors instead of releasing them into the air. To ensure the system is sealed, the PCM runs self-tests under specific conditions.
During a typical small-leak test, the PCM opens the purge valve to create vacuum in the system, then seals the system by closing the purge and vent valves. The PCM monitors how quickly vacuum decays using a fuel tank pressure (FTP) sensor. If vacuum drops too quickly, it indicates a leak and may trigger code P0456.
Some vehicles use different strategies. Certain older Chrysler, Dodge, and Toyota models use a leak detection pump that checks for leaks while the engine is off. Later Chrysler/Dodge vehicles use an Evaporative System Integrity Monitor (ESIM), which detects pressure changes in a sealed fuel tank as temperatures rise and fall.
On some Jeep models, such as the 2014 Jeep Grand Cherokee Laredo 3.6L V6, the ESIM switch alone is used for EVAP leak diagnostics. The FTP sensor is not involved in leak detection on these systems. Extreme temperature changes can affect test results, so conditions during diagnosis matter.
Because EVAP leaks are usually very small, symptoms are minimal. Most drivers will notice:
The vehicle typically runs and drives normally despite the code.
Possible causes of a P0456 code include:
A damaged fuel tank or an improperly sealed fuel pump after tank removal can also introduce small leaks.
A P0456 code is not an immediate drivability concern and won’t leave you stranded. However, it allows fuel vapors to escape, increasing emissions and potentially causing a failed emissions or smog test. Ignoring the issue for too long can also stress other EVAP components, leading to more expensive repairs later.
Diagnosing a small EVAP leak can be challenging. A practical approach includes:
Fixes depend on the underlying cause:
Keep in mind that repair methods can vary by vehicle. What works for one make may not apply to another.
Yes, the vehicle usually drives normally, but the check engine light will remain on until the issue is resolved.
Yes, a loose or damaged gas cap is one of the most common and simplest causes of this code.
The code must be cleared with a scan tool, and the EVAP monitor must run again to confirm the fix.
If the underlying leak is still present, the PCM will detect it again during the next EVAP self-test.
Yes, EVAP tests usually only run when the fuel level is within a specific range.
Yes, especially on systems like ESIM that rely on pressure changes from temperature variation.
Costs vary widely. Simple fixes like a gas cap are inexpensive, while diagnosing small leaks can take more time and effort.
Yes, if seals are misaligned or components were damaged during tank removal.
Yes, an active EVAP leak code can result in a failed emissions or smog inspection.
If tightening or replacing the gas cap doesn’t resolve the issue, or if you can’t locate obvious damage, professional diagnosis is recommended. Small EVAP leaks can be extremely difficult to pinpoint without specialized equipment, and a technician can confirm repairs before the code returns.
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.