Trouble Code: P0440 (Evaporative Emission Control System Malfunction)


The evaporative emission control system is an environmentally friendly piece of auto technology. Its job is to contain fuel vapors in your vehicle and prevent them from escaping into the atmosphere and polluting it. Fuel vapor is a natural occurrence whenever you pump gasoline into your vehicle. Instead of polluting the outdoors, the evaporative emission control system causes the vapors to flow into the engine. Then it is ignited along with the fuel and air mixture.

Trouble Code P0440

The engine control unit of a vehicle is in constant communication with the evaporative emission control system. If the engine control unit detects a malfunction in this system, it will generate diagnostic trouble code P0440. The specific type of malfunction with the system will not be indicated here, though. You could be dealing with anything from a bad vapor pressure sensor to a leak in the system.  Only a thorough inspection of your system will determine the exact cause.

The engine control unit keeps a close eye on the vapor pressure. The fuel vapor normally goes through special vapor lines in the fuel tank before it enters the engine. If the engine control unit detects a drop in the vapor pressure, this could cause trouble code P0440 to be generated. Surprisingly, in many of these cases, the cause is something as simple as the gas cap being too loose. If you forget to screw the gas cap back on tightly, this could cause a fuel vapor problem in your system.


The first thing you will notice from a malfunctioning evaporative emission control system is the “Check Engine” warning light coming on. Since this light could mean any number of things, you should immediately connect a diagnostic scanner to your powertrain control module to see what is happening. If you are not experiencing any other symptoms at this point, then you will have no idea what is going on until you run the diagnostic check. If the problem is your evaporative emission control system, then P0440 will be your trouble code.

Read also: Explained Trouble Code: P0300 (Random Multiple Cylinder Misfire Detected)

If the problem is related to a fuel vapor leak, you may smell the fuel vapor aroma in the air of your passenger cabin. And if you happen to live in a state which requires you to get emissions testing every 6 months, you will likely not pass the test if you have a malfunctioning evaporative emissions control system. So, be aware of these issues and deal with them quickly after you first notice their existence.


Leave a Comment

This site uses Akismet to reduce spam. Learn how your comment data is processed.