CodelampTwo codes together
P0442 and P0455 together: a small and a large fuel vapor leak
P0442
- In plain words
- The fuel vapor system has a small leak.
- Standard name
- Evaporative Emission System Leak Detected (Small Leak)
- System
- Fuel vapor (EVAP) system
P0455
- In plain words
- The fuel vapor system has a large leak, often a loose or missing gas cap.
- Standard name
- Evaporative Emission System Leak Detected (Large Leak)
- System
- Fuel vapor (EVAP) system
General information, not a mechanic's diagnosis: have a mechanic confirm before any repair.
What the computer saw
P0442 is a small leak and P0455 a large one in the fuel vapor system. They often come from one failed part that leaked a little before it leaked a lot, such as a gas cap seal or a valve.
Likely causes, most common first
- A worn or loose gas cap. First to check, and the cheapest.
- A vent valve that does not close. It can leak a little or a lot.
- A cracked EVAP hose. A small crack that grew.
- A purge valve stuck open. Less common, and often sets its own code too.
What you can note yourself
- Check the gas cap's seal for cracks and tighten it until it clicks.
- Allow several days of normal driving for the computer to rerun its test.
What to tell the shop
- Both codes, and whether you checked the cap.
- Ask for a smoke test before valves are replaced.
This page gives no verdict on whether a car is safe to drive; a mechanic can.