| EVAP Control System Leak Detected Very Small Leak
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Table of Contents
- What Does Code P0456 Mean?
- Where is the P0456 sensor located?
- What are the common causes of code P0456?
- What are the symptoms of code P0456?
- Get Help with P0456
What Does Code P0456 Mean?
SPECIAL NOTES: Although generic OBD II trouble codes such as P0456 – “EVAP Control System Leak Detected Very Small Leak” can, and do affect all OBD II compliant vehicles, some vehicle makes and models are sometimes more susceptible to some generic trouble codes than most others under real-world driving and operating conditions. Therefore, this article will discuss generic trouble code P0456 – “EVAP Control System Leak Detected Very Small Leak” as it applies to the Toyota models that are most commonly affected by it. END OF SPECIAL NOTES.
OBD II fault code P0456 is a generic trouble code that is defined as, P0456 – “EVAP Control System Leak Detected Very Small Leak” and is set when the PCM (Powertrain Control Module) detects a small leak in the EVAP system. Note that while EVAP (Evaporative Emissions Control) systems can generally not determine the exact size of a leak, small or very small leaks are typically taken to be leaks that are smaller than about 0.020 inches in diameter.
Although the technical implementation of EVAP systems varies greatly between different vehicle makes and models, the function of all EVAP systems on all vehicle makes and models is to trap and contain fuel vapors in a charcoal-filled canister until the trapped vapors can be transported to the engine to be combusted along with the regular air/fuel mixture.
However, for emission control purposes, all EVAP systems have to incorporate a leak detection system that is capable of performing self-diagnostic tests at certain points before, during, and after trips to verify the integrity of the EVAP system. In practice, all EVAP systems use all of the components of the system to perform self-tests, and these components include the fuel tank itself, the fuel filler cap, various vacuum hoses, a charcoal canister, vent, and purge valves, and a variety of pressure and flow sensors.
Here is a generic description of how the EVAP leak detection system works on Toyota vehicles-
Self-tests will generally only initiate after a vehicle has been parked for about five hours or until the engine temperature has dropped to a predefined level. At this point, the PM closes the vent and purge valves to allow a dedicated vacuum pump to generate a negative pressure (vacuum) in the fuel system. If no leaks are present, the vacuum will hold steady for a set amount of time. If, however, a small leak is present in the EVAP system, the vacuum will decay, and the PCM will calculate the approximate size of the leak based on the rate of vacuum decay.
Nonetheless, to improve the accuracy of self-tests several enabling conditions must be satisfied before an EVAP self-test will initiate. These include, among others, the ambient temperature being within a predefined range and the fuel tank being between about 25 percent and about 75 percent full.
It is important to note that although the presence of small or very small leaks in the EVAP system will not influence the normal operation of the vehicle, the EVAP system is considered to be a primary emissions control system and, therefore, the PCM will set an appropriate code and illuminate a warning light when it detects leaks in the EVAP system.
Where is the P0456 sensor located?
This image shows the primary EVAP system components of a 2002 Toyota Forerunner. In the case of code P0456, which denotes a very small leak it is often necessary to remove the entire EVAP assembly (as shown here) from the vehicle for inspection and repair, since some conventional diagnostic methods like filling the system with smoke often do not reveal very small leaks.
Be aware, though, that on high-mileage vehicles, it may be necessary to replace all major EVAP components, including all rubber/flexible hoses to resolve issues with small leaks definitively and reliably.
What are the common causes of code P0456?
Some common causes of code P0456 could include one or more of the following-
- Hardened or cracked vacuum hose(s)
- Cracked charcoal canister
- Leaking vent valve
- Leaking purge valve
- Damaged or leaking fuel filler cap
- Damaged or leaking fuel filler neck
Damaged or leaking vacuum check valves
What are the symptoms of code P0456?
Common symptoms of code P0456 could include the following-
- Stored trouble code and illuminated warning light
- Depending on the nature of the problem, one or more additional trouble codes may be present along with P0456
- The odor of fuel may be present in or around the vehicle
- The EVAP readiness monitor will not run to completion
- The vehicle will not pass a mandatory emissions test
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