P0440
Evaporative Emission Control System Malfunction
Get Your FREE AI Diagnostic Report
Enter your vehicle for a personalized diagnosis for code P0440
OBD2 code P0440 indicates an Evaporative Emission Control System (EVAP) malfunction detected by your vehicle's onboard diagnostics. The EVAP system is designed to prevent fuel vapors from escaping into the atmosphere by capturing them in a charcoal canister and routing them back into the engine to be burned during combustion. When the engine control module (ECM) detects that the EVAP system is not maintaining proper pressure or function, it triggers the P0440 code and illuminates the Check Engine Light. This is a generic powertrain code that applies to all OBD2-equipped vehicles manufactured from 1996 onward, though specific diagnostic procedures may vary by manufacturer.
While P0440 is not typically an immediate safety concern that will leave you stranded, it should be addressed within a week or two. This code indicates your vehicle is releasing more fuel vapors into the atmosphere than allowed by emissions regulations, which is harmful to the environment and will cause your vehicle to fail an emissions inspection. Additionally, the underlying issue may worsen over time, potentially leading to failed emissions tests, reduced fuel economy, and in some cases, damage to other EVAP system components. The good news is that P0440 is often caused by simple, inexpensive issues like a loose or faulty gas cap, making it one of the more affordable and DIY-friendly trouble codes to resolve.
If you receive a P0440 code, start by checking your gas cap—ensure it's tight and inspect the seal for cracks or damage. If the gas cap appears fine, a professional diagnostic smoke test can help locate leaks in the EVAP system hoses and connections. Many auto parts stores offer free code reading services, and some may even clear the code after you've tightened or replaced the gas cap to see if it returns. More complex repairs involving valves or the charcoal canister may require professional diagnosis and repair, but even these repairs are typically moderate in cost compared to other powertrain issues. Regular maintenance, avoiding overfilling your fuel tank, and replacing your gas cap every few years can help prevent P0440 and keep your EVAP system functioning properly.
Severity
Symptoms
- •Check Engine Light illuminated
- •Slight fuel smell around the vehicle
- •Failed emissions test
- •Difficulty filling fuel tank (pump keeps clicking off)
- •Occasional rough idle when tank is full
- •Slightly decreased fuel economy
Likely Causes
The most common cause of P0440 is a gas cap that is not properly tightened, has a worn seal, or is missing entirely, allowing fuel vapors to escape from the EVAP system.
Rubber hoses and plastic lines in the EVAP system can crack, deteriorate with age, or become disconnected, creating leaks that prevent the system from maintaining proper pressure.
The purge valve controls the flow of fuel vapors from the charcoal canister to the engine. If it sticks open, closed, or fails electrically, the EVAP system cannot function properly.
The vent valve seals the EVAP system during leak tests. A failed vent valve can prevent proper pressure testing and cause the system to fail diagnostics.
The charcoal canister stores fuel vapors and can become saturated with liquid fuel (often from overfilling) or physically damaged, compromising EVAP system performance.
Estimated Cost
Professional Repair
Includes parts + labor
Common Fixes
- Replace or properly tighten the gas cap ($15-25)
- Repair or replace damaged EVAP hoses and lines ($50-150 DIY, $150-300 professional)
- Replace purge valve/solenoid ($50-120 DIY, $150-350 professional)
- Replace vent valve/solenoid ($60-150 DIY, $180-400 professional)
- Replace charcoal canister ($100-250 DIY, $250-650 professional)
Shop Parts
Videos
How To Fix Large Evap Leaks On Your Car P0455
Scotty Kilmer
Check Gas Cap Light Fix
ChrisFix
Check Engine Code Says EVAP? How to Diagnose EVAP System Problems and Leaks
1A Auto