The P0455 error code indicates a leak in the vehicle’s Evaporative Emission Control System (EVAP). It is known to be a tricky code to identify correctly. However in this article, we are going to look at what causes it and how to diagnose and fix it.

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 P0455 code is specifically for small leaks in the EVAP system.

The EVAP system has four major components. They include:

The gas/fuel tank:

The gas tank is built with additional space so that when the gas expands, it does not leak over and cause an EVAP error code.

The fuel cap:

In old vehicles, the gas cap has a pressure relief valve. This is before OBD II was introduced. It is however sealed in newer vehicles (vehicles made from 1996 onwards). Always remember that when replacing the fuel cap, it should be the same as the original that came with the car.

The liquid-vapor separator:

This is a little separator that prevents gasoline from dripping into the vent line to the EVAP system canister. It is dangerous when gasoline goes directly to the canister. This is because the gasoline will cause the canister to lose its ability to store gas vapors.

It is located on the top of the gas tank or in some vehicles, on the overflow tank. The liquid-vapor separator rarely develops any issues. The most common issue is when the liquid becomes polluted with debris and rust that case an external leak. Different model cars have different liquid-vapor separators.

In such vehicles, a float and needle are placed inside the separator and when liquid enters, the float rises and pushes the needle to close the vent. Others use a foam-filled dome-shape material on top of the gas tank. Vapor passes through the foam but liquid is trapped by the foam.

Symptoms of error code P0455

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. EVAP leaks can easily be identified by noticing some of the symptoms. The following are the most common symptoms of the P0455 error code.

  • The engine check light comes on
  • Reduced fuel efficiency
  • A smell of fuel around the gas tank

Causes of error code P0455

A P0455 error code can be caused by a variety of damaged components in the EVAP system. If any of these components are loose or damaged, fuel vapor can escape meaning a P0455 error code will be detected. The following are the causes of this error code.

Gas Cap

This is the most common cause of this error code. Gas caps tend to be left hanging loose after gas refills and this allows gas vapor to escape into the atmosphere.

Damage to the neck of the gas cap also prevents the gas cap from closing tightly. Always ensure to replace damaged gas caps with the same as the one from the manufacturer

Cracked EVAP pipes and hoses

The pipes along the EVAP system sometimes crack due to old age and wear and tear. A cracked hose means that fuel vapor will leak into the atmosphere. Once the fumes leak, a P0455 error code is detected by the scanner

Failed valves

If the control valves and purge valve are damaged, gas fumes leak into the air causing a P0445 error.

Clogged canister:

The EVAP system has a charcoal canister surrounding the pipes. If the canister clogs, the error code is detected

Cracked Cylinder:

Any cracks in the EVAP system allow gas fumes to escape into the air. Once this happens, an error code is easily read by the OBD II scanner.

How to diagnose P0455 code

To diagnose a P0442, you need the following tools: OBD II Scanner, a digital mutimeter and a smoke machine. Once you have these tools, follow the following steps to diagnose and repair the problem.

  1. Scan the car for other potential trouble codes. This is done to identify problems that should be fixed before the P0442 code. Problems with fuel injection and fuel pressure should always be fixed first while the P0442, P0440, P0446 are EVAP leaks and are after.
  2. Inspect the gas cap to make sure it is not loose
  3. Check the EVAP system pipes and hoses for leaks and cracks and make sure they are tightly connected. If they are, use the smoke machine to do a smoke test. This is done because P0442 code means there is a small leak that cannot be found or seen by the naked eye.
  4. Check the fuel tank for leaks
  5. Use the multimeter to test the charcoal canister vales. You should always disconnect the valves when testing.

How to fix P0455 code

To be able to fully fix this problem, it is important to know where the root cause of the problem is. To do this, start checking from the most common diagnosis as you go into more complex ones.

After each fix, clear the error codes and then rescan using the OBD II scanner to see if the problem has been fixed. The following steps show how to fix a P0455 error code.

  1. The first thing you should check is the gas cap. Whether or not you see a problem in the tank, you should always replace the gas cap. This is because gas caps develop very small damage in the neck that cannot be seen by the naked eye. If this is the problem, the error code is cleared after retesting. This is a cheap fix and should always be done first. Clear the codes and the rescan the vehicle. If the error code persists, move on to the next step.
  2. Do a smoke test of the EVAP system and repair the small leaks that you find. Before doing this, ensure that the hoses are firmly closed. Clear the codes and the rescan the vehicle. If the error code persists, move on to the next step.
  3. Replace the control and purge valves to eliminate the possibility. Clear the codes and the rescan the vehicle. If the error code persists, move on to the next step.
  4. Clean the charcoal canister and do it using compressed air. The pressure of the air should be 50 psi. Clear the codes and the rescan the vehicle. If the error code persists, move on to the next step.

Conclusion

The cost of repair for P0455 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 P0455 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'.