P0456 code – Causes, information & Fix

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 OBD codes play a huge role in identifying vehicle’s problems. The P0456 code is the code used to identify a problem in the car’s Evaporation Emission Control system. It indicates a small leak has been detected in the EVAP system. In this article, we are going to look at what causes EVAP leaks and how to fix them.

An EVAP system is one of the largest systems found in vehicles. It is made up of many components located all through the car from the front to the back.

Evaporative Emission Control System (EVAP) was introduced in vehicles as a means to preserve the environment. Its main function is to prevent fuel vapor from escaping the fuel tank and fuel system into the atmosphere.

EVAP systems rarely suffer from damage but when they do, finding the leak can be a difficult task to the large nature of the system, especially when the leak is small. The P0456 code is specifically for small leaks in the EVAP system.

Since the EVAP system is self-diagnostic, it usually does not need maintenance. They can still however develop faults and cause the engine light to turn on. When the engine light comes on, it prevents the car from passing an OBD II emission test.

The self-diagnostic monitor EVAP was introduced in 1996 and all vehicles since then have had it. It checks for gas vapor leaks and whether the gas caps are loose or missing. If it finds any of these, it sets a fault code and turns on the engine light.

Symptoms of P0456 error code

The P0456 error code does not affect the driving experience of your car. However there are noticeable signs that you might have this problem.

Smell of gas

When you smell gas around the fuel tank of your vehicle, it could indicate a P0456 error code. This is because there might be a leak in the EVAP system of the car. If there is a leak, gasoline fumes will escape into the air and you will smell fuel.

Check engine light comes on

The engine light comes on as a P0128 error code affects the engine. When there is the P0128 error code, the temperature can be even half this when the engine is started.

The engine control unit uses this information to regulate the amount of air and fuel mixture. This process will not happen if the engine does not reach the optimum temperature of 160.

Poor acceleration and reduced engine performance

If you realize that each time you accelerate the vehicle hesitates or struggles too much to go faster, it could mean that your mass airflow sensor is has gone bad. This is especially if you experienced the previous two symptoms.

If the acceleration is coupled with a jerking motion, this just confirms the P0128 error code. This problems is caused by the engine not receiving the right amount of air and fuel. Although a lot of things can cause poor acceleration and jerkiness, when coupled with the previous symptoms, it means that the mass air flow system is bad

Poor fuel economy

If you notice you’re suddenly spending more on fuel than you used to before, it means the vehicle’s fuel economy has been reduced. A bad mass airflow sensor will cause the engine to run too rich which in turn will lead to poor fuel economy.

An engine is said to be running rich when the amount of fuel in the cylinders is excess compared to the air in the cylinders. The engine control unit might send too much fuel in the cylinders when it receives wrong information from damaged mass airflow sensors. When you find all these symptoms in your car, there is a very high chance that the problem is in the mass airflow sensors.

Causes of P0456 error code

Other than the common leak, a P0456 error code can be caused by a variety of reasons. The reasons include the following.

  • Leaking fuel tank
  • Leaking charcoal canister

Leaks in the hose

Leaks are caused by cracks in the hoses. The cracks form as a result of corrosion due to old age. Sometimes, hard particles may hit and crack the EVAP hoses.

Damaged or loose gas cap

When the gas cap is loose or damaged, you will smell gasoline around the fuel tank area. This causes a P1456 error code since gas fumes are in the air

Faulty valves

Faulty valves allow gas vapor to escape into the atmosphere causing a P0456 error code.

How to diagnose P0456 code

To diagnose a P0456, you need the following tools: OBD II Scanner, a digital mutimeter and a smoke machine and a small handheld vacuum pump. Once you have these tools, follow the following steps to diagnose and repair the problem.

First scan the car for other related error codes such as the P0440, P0441, P0442, and P0446. If you find any of these codes, fix them first. After doing this, check the gas cap for any damage. Inspect the neck of the cap, and the threads of both the cap and the fuel tank.

If there is any noticeable damage, replace the cap and sharpen the threads using a special tool found in auto repair shops. Inspect the metallic pipes of the EVAP system for cracks and any other damage.

Tighten any loose hoses and replace the damaged ones. Use the OBD II scanner to close the vent solenoid and thereby seal the EVAP system. Check the fuel tank pressure (FTP) sensor and if the reading is consistent, the system is has been sealed properly.

After this, check the vents located near the charcoal canister and make sure they are functioning well and if they are receiving power. To check for power use the digital multimeter.

If they are not receiving any power, the problem is likely to be in the wiring or the powertrain control module. If there is power however, use the vacuum pump to test the operations. Finally, use the smoke machine to carry out a smoke test to check for leaks in the EVAP and exhaust system.

How to fix P0456 error code

A lot of trial and error goes into fixing a P0456 error code. This is because finding and fixing tiny leaks is difficult task that takes some time. There is also the fact that not every test finds every leak. While this error code mostly means that there is a leak, it could also sometimes mean that there is a damaged component.

  1. Check the gas cap for any damage. Inspect the neck of the cap, and the threads of both the cap and the fuel tank. If there is any noticeable damage, replace the cap and sharpen the threads using a special tool found in auto repair shops.
  2. Inspect the metallic pipes of the EVAP system for cracks and any other damage. Tighten any loose hoses and replace the damaged ones


The cost of repair for P0456 is quite affordable. It is important to practice good vehicle maintenance habits to prevent damage to the EVAP system. Other than a slight odor and reduced fuel efficiency, it is difficult to identify a P0456 code. This is why regular maintenance is recommended.

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Steven Reilly is a qualified mechanic and his passion for cars goes beyond just the technical aspects. He is also an amateur racer and all round car enthusiast. When he is not driving them, he can often be found in his garage under the hood of a rare model. Steven Reilly has lost track of the number of hours he has spent setting up his fine collection of rebuilt models. He believes that cars can provide a constructive and fun opportunity to teach the youth important life skills. In line with this, he is developing a community outreach program, potentially dubbed ‘Cars for change'.
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