The 1998 Dodge truck lineup included the Dakota two-wheel- and four-wheel-drive pickups, the Durango four-wheel-drive SUV and the Ram 1500, 2500 and 3500 pickups. Each of the full-size Ram trucks were available in two-wheel- and four-wheel-drive packages. Each of these 1998 Dodge trucks, and any vehicles built after 1995, are equipped with second-generation onboard diagnostic computers, or OBDII systems. The P0455 trouble code is not vehicle-specific but is a common code referring to a massive evaporative emissions control leak. This leak can be simple or quite troublesome to fix, depending on the location of the leak.
Open the fuel door on the side of the truck. Release the fuel cap from the truck completely to allow the vapors in the vapor return line to be emitted from the line. Replace the fuel cap as tight as it will go. Some fuel caps on the Dodge trucks were designed to click and create some resistance when they are fully tightened. Continue turning the cap until you reach complete resistance or hear a clicking.2
Enter the cockpit of the truck you are working on and insert the ignition key into the ignition cylinder. Turn the key to the "II" or accessories position. Install the OBDII code reader into the OBDII interface port, which is located just beneath the dashboard on the driver's side of the truck. The shape of the port matches the shape of the plug, so it should not create a problem locating this device. Turn the power on to the code reader once you have successfully plugged it into the dashboard.3
Go through the sequence of prompts that the reader puts you through, using the "UP" and "DOWN" arrows to make your choices. Hit the "READ" button to allow the reader to accept each of your answers. You will be prompted for foreign or domestic vehicle, year, make, model, and then what function you want the computer to perform. Choose the "Read Diagnostic Codes" selection and press "READ." When the computer is done you will receive the P0455 code, along with any other code your truck is producing.4
Press the "ERASE" button on the reader to erase the existing P0455 code. Start the truck and drive the truck for no less than 10 miles. If the "Check Engine" light does not return, then you simply had a loose fuel cap. If the P0455 code returns within the 10-mile drive, return to your work and move to Step 5.5
Remove the fuel cap completely from your Dodge truck, assuming the initial test failed to remove the P0455 code. This does not mean that your fuel cap is not bad. Take the fuel cap to your local auto parts store and purchase a matching fuel cap. Return to your truck and install the new cap. Make sure the cap is securely sealed. Repeat Steps 3 through 5 to again erase the P0455 code, and test drive the truck to see if the code returns. If it does not return, you had a bad cap.6
Retest the trouble codes in the OBDII computer by performing another test with the code reader. At this point, if you have cured the evaporative emissions leak, then you are going to have to perform a visual inspection. Kneel down just in front of the rear driver-side tire. You will see two pipes going from the fuel fill neck to the fuel tank. These are the fuel filler tube and the evaporative emissions tube or vapor return tube. Check both of these tubes out thoroughly, feeling them with your hand.7
Place your nose near the rear tire and inhale deeply to sense if you can smell fuel vapors or gas. If you smell gas, or if you locate a puncture between the fuel filler tubes and the tank with your hand, get your truck to a local shop as soon as possible. A leaking neck or vapor tube can ignite with the slightest spark and will need immediate attention from a trained professional.