General fault code for Evaporative Emission Control System Malfunction
OBD-II code P0440 represents a general fault in the Evaporative Emission Control (EVAP) System. Basically, this code means that something in the EVAP system is broken. Another code will typically accompany P0440, often in the P044X chain (where "X" represents any number).
What The Evap System Does
The EVAP system is responsible for controlling the fuel vapors in your Toyota's gas tank. The vapors are captured from the tank, sent into the EVAP system, and stored in a small canister filled with charcoal. The aptly-named charcoal canister will then send the vapors into the fuel system for burning in the engine when the vehicle is running. The EVAP system has many components, any one of which could be broken when a P0440 is triggered.
A few easy solutions can be tried before serious diagnostics and time is spent trying to find a problem.
What Triggers The P0440 Trouble Code
Much of the time, when the P0440 is the only code triggered, it's going to be one of three things:
- a faulty or leaking gas cap,
- a failed purge solenoid, or
- a plugged canister
Start by removing the gas cap and checking the O-ring inside for debris or breaks. If all is OK, put it back on the filler neck and click until it's tight. Then jiggle it to see if it has any "give" from in to out. If so, it may need replacing as it may be breaking the seal it should be making with the filler neck. If all is OK, clear the trouble codes from the computer and drive for another day to see if they re-trigger.
If they do, test the purge solenoid and the canister and replace them if necessary. Anything more than that, and you will need to do a full test of the entire EVAP system, including all hoses, sensors, valves, etc.
For a comprehensive list of trouble codes, check out this article on the Toyota Parts Center Blog.