The 2003 Dodge Ram uses an electronic control module (ECM ) to control all of the electronic functions of the truck. It also has a second-generation on-board diagnostics system (OBD II) that monitors the hundreds of components that make the Ram function properly. If something stops working on the truck, the "Service Engine" light comes on and does not turn off until the broken component is replaced or the ECM is reset.
Remove the negative cable terminal from the Ram's battery with an adjustable wrench. Leave the battery disconnected for 20 minutes to reset the computer. Reconnect the negative cable and drive the vehicle for 50 miles to recalibrate the computer. If the code does not come back on, the issue was intermittent. If the code returns, move to the next step.
Remove the gas cap and put it back on, making sure that it's tight. The Dodge Ram has a sensor that measures fuel emissions. If the computer misreads the emissions from the gas cap, it generates a code. After you remove and reattach the gas cap, remove the negative battery cable and repeat Step 1.
Change the oxygen sensors located just above the catalytic converters. The oxygen sensors look like spark plugs with a small wire coming out of them. They measure the amount of oxygen processed by the engine and expelled as exhaust gas. If the sensor fails to read the levels properly, it triggers a code. Worn-out oxygen sensors commonly cause error codes. Locate the sensor directly above the catalytic converters on the exhaust pipe. Disconnect the wiring harness to the sensor by pulling the two connectors together and remove the sensor with an adjustable wrench. Repeat Step 1.
Drive your Ram to a Dodge dealer or certified repair facility and ask for a diagnostic test. They have OBD II scanners that read the code and indicate the component that needs to be replaced. OBD II scanners are available from auto parts stores but they can be costly.
