If your check engine light turns on for an EVAP code like P0455 (large leak) or P0442 (small leak), there is a small or large leak in the evaporative emission control system (EVAP) system. Learn how to find an EVAP leak in your car by checking these three common causes of P0455 and P0442 codes.
EVAP Code P0455 or P0442 Causing a Check Engine Light? How to Find an EVAP Leak
You might be driving and not notice any issues but then the check engine light comes on for code P0455 or P0442. If it reads for a large or small EVAP system leak, these are the most common causes.
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1. Gas Cap and/or Fuel Filler Neck – P0442
Check the Gas Cap
A broken gas cap will usually cause a small leak in the EVAP system and trigger code P0442.
Make sure the gas cap secures tightly and isn’t loose. Remove the gas cap and check the seal. Make sure the seal isn’t cracked, breaking, or has missing pieces.
Read more on how to inspect the gas cap
Broken or Rusted Fuel Tank Filler Neck
Check the filler neck for rust build up. If you find minimal build-up, you can sand it off with sandpaper or emery cloth. If the fuel filler neck is too damaged to be fixed, replace it. We recommend replacing the gas cap at the same time as the fuel filler neck.
2. Faulty Purge Solenoid Valve – P0442 or P0455
The purge solenoid brings vacuum to the EVAP system. Vacuum enters through the intake manifold and an electrical connector controls the pure solenoid valve. If the purge valve leaks, it could trigger a P0455 or P0442 code, but it might also trigger a different EVAP code.
If the purge solenoid is defective, replace it. Steps include removing the hoses and disconnecting the electrical connector.
3. Faulty Vent Solenoid Valve – P0442 or P0455
When the purge valve opens, a vacuum line sends vacuum to the vapor canister. Charcoal in the canister eliminates fuel vapors from entering the atmosphere, and vacuum to the canister puts vacuum on the fuel tank by a line connected to it.
The canister has another line that connects to the vent solenoid valve. When the system is not operating, the vent valve will sit open. The gas tank, canister, lines, and vent valve need to be sealed. When the system is up and working, the valve closes and the purge valve up front opens. The EVAP canister vent solenoid valve will vent off excess vacuum, and it can trigger a large or small EVAP leak code if there’s a problem.
You might be able to tell if the vent solenoid valve is defective with an eye test. There might be a crack in the hose or a crack in the solenoid. If any pieces of this system are broken, replace them.
The valve can also clog or leak, and sometimes the problem is internal and can’t be seen. Debris and other contaminants can also make it difficult to close, and this will turn on a check engine light.
You can test the system with a smoke tester if a visual test does not show any problems.
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If your fix resolves the issue, will the light reset automatically and if so how soon?