Evaporative Emission Control System Leak Detected (Fuel Cap Loose/Off)
Indicates a leak in the evaporative emissions system due to a loose or missing fuel cap.
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What it means (plain English)
Your car's computer thinks there’s a gas tank leak because the fuel cap isn’t sealing properly or is missing altogether.
What the computer is actually seeing
The system monitors pressure in the fuel tank and associated components. If it detects that the pressure is dropping below normal due to a leak, it will trigger the P0457 code.
What a healthy reading looks like
The fuel tank pressure should remain stable; normal values typically range from -2 to 2 inches of water column under operating conditions.
Guided diagnostic — the DiagCoach way
Don't just throw parts at it. Walk through these in order — each step tells you whether to keep going or stop and fix what you found.
- 1Check if the fuel cap is loose or missing. If it's not secured, tighten or replace it as necessary.
- 2Inspect the fuel cap O-ring for damage or wear. Replace if it’s cracked or missing.
- 3Using a smoke machine, check for vapor leaks in the EVAP system components including hoses and the canister.
- 4Test the fuel tank pressure sensor for correct operation. Expected resistance is typically between 1-5 ohms. Replace if faulty. After repairs, clear the code and retest.
Common causes
- Loose or missing fuel cap
- Damaged O-ring on the fuel cap
- Cracked or damaged fuel lines
- Faulty evaporative emissions canister
- Failed purge valve
Typical repair cost
$$
Related codes
Frequently asked questions
Is it safe to drive with this code?
Yes, but you may have reduced fuel efficiency and increased emissions. Fixing it soon is recommended.
Will this code return if I just replace the fuel cap?
If the cap was the only issue, then likely no. However, if there are other leaks, the code may return.
Why do I see this code with P0455 and P0456?
These codes address similar issues with the EVAP system but indicate different leak sizes or particular conditions. It's common to see them together.
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