How do you ckeck trouble codes with a jumper wire?

To check trouble codes using a jumper wire, first locate the diagnostic connector in your vehicle, usually found under the dashboard. Use a jumper wire to connect terminals labeled "B+" and "TE1" (or "E1" depending on the vehicle) in the connector. Turn the ignition key to the "ON" position without starting the engine, and watch the check engine light; it will blink a series of codes that correspond to stored trouble codes. Count the blinks to decode them based on your vehicle's service manual.