I have the V6, but I am looking at the FSM for your vehicle right now

Connect the "Trouble Code Test" terminals with each other. (In the Trooper, these are found in the console in front of the ECM.) You can lift the little tray out of the front of the console. There should only be two connectors that can be connected together.

Turn the key to the "On" position without starting the vehicle.

The ECM will chause the "Check Engine" light to flash Code 12, indicating that the ECM diagnostics are working. Code 12 with flash three (3) times, followed by any other trouble codes stored in memory. Each additional code will flash three times, starting with the lowest code, and then start over with Code 12.

Record any codes other than 12 and post the results here and one of us with look them up for you.