Your check engine light might seem like an incomprehensible warning telling you that you're about to start feeding money into your car, but it's a useful diagnostic tool. Although the light doesn't provide much information, it only turns on when your vehicle's computer has at least one stored code. These codes can give you drastically more data about your problem.
Several codes, such as P0455, can indicate trouble with your car's evaporative emissions or EVAP system. Your EVAP system prevents gasoline vapors from escaping to the atmosphere by purging them into your engine's air intake. An EVAP code tells you that there's something wrong with this system, which may be due to one of these three common issues.
1. Gas Cap Issues
You've probably heard that you should check your gas cap whenever you have a check engine light. A loose gas cap can cause an EVAP system code since the computer needs to check for the correct pressure in the EVAP system. A leak at the gas cap allows air (and gasoline vapors) to escape, potentially triggering this warning code.
However, a loose cap isn't the only issue you should investigate. You also want to remove your cap from the car and carefully inspect it. There's a seal around the inner edge of the cover that keeps the system closed. If this seal appears worn, broken, or otherwise in poor condition, you may need to replace your gas cap to solve your EVAP system code.
2. Vent or Purge Issues
There are two locations where your vehicle will intentionally allow air into the EVAP system. One of these is the purge valve, which manufacturers typically install in the engine bay. The purge valve pulls gasoline vapors into your car's engine from the gas tank. The EVAP canister near your fuel tank also contains a vent solenoid that will periodically open.
If either one of these components fails, it will affect the system's ability to maintain the correct pressure level. As a result, your car's computer will fail to detect adequate pressure in the EVAP system and trigger a check engine light. A qualified technician can usually check both of these parts relatively quickly to determine if they are at fault.
3. Significant Leaks
Unfortunately, there may also be a more significant leak in your fuel system. Leaks at the fuel tank, EVAP canister, or any of the lines in the EVAP system will trigger an error code. Although your car will probably still drive fine, you may smell unburnt gasoline. You're also most likely to receive a P0455 code in these cases since this code indicates you have a large leak in the system.
While EVAP codes don't typically produce drivability issues, you should always have them diagnosed and repaired as soon as possible. Releasing unburnt gasoline vapors can harm the environment and will likely cause your car to fail any state emissions tests.
For more information, take your car to an auto repair professional.