Code P0440 on the 2003 Dodge Dakota is a trouble code relating to the evaporative emission, or EVAP control system. The EVAP system works by routing gas fumes into a charcoal canister, and they are later routed into the engine for combustion. This code can be set by several causes and can be difficult to diagnose.
The EVAPsystem as a whole is designed solely to prevent fuel vapor and fumes from escaping into the earth's atmosphere. Even though there are often no changes to performance of the vehicle, it is important to check and maintain the entire system regularly. In states that perform emissions checks on vehicles prior to registration, a fault in the EVAP system will most likely cause your Dakota to fail the emissions test.
Loose Gas Cap
The most common reason for this code is an improperly tightened gas cap. The gas cap should be tightened until it clicks three times. The best way to see if this was the cause is to tighten the gas cap and drive the vehicle as normal, if the code comes back again, then it is possible the gas cap is leaking.
Faulty EVAP Purge Solenoid
The EVAP purge solenoid is responsible for opening the valve that allows the fuel fumes to be routed from the purge canister to the engine. If the purge solenoid fails, then it is likely the valve is staying closed and the fumes are not returning to the engine, triggering the P0440 code. Normally, the location of most EVAP system components are displayed on a sticker under the hood of the vehicle.
EVAP System Hoses
Leaking or damaged hoses in the EVAP system are another common cause for code P0440 in the '03 Dodge Dakota. Following the diagram under the hood of the vehicle, trace as many of the hoses and lines as possible and inspect them for damage, as well as the purge canister and replace as necessary.