- 1). Connect the scan tool to the vehicle's onboard computer. Attach the scan tool's OBD port reader to the OBD port, located under the driver's side dash.
- 2). Turn on the scan tool, and allow the tool to boot to the ready state.
- 3). Start the engine on the vehicle.
- 4). Access the scan tool's menu to view the fuel trim measurements reported by the vehicle's on-board computer. The exact steps required depend on the manufacturer and model of the scan tool. Consult the owner's manual for specific instructions.
- 5). Drive the vehicle, and monitor the scan tool for fuel trim adjustments at different throttle positions. Typical throttle positions include idle, one-third, one-half and wide-open throttle. Fuel trim data might be different in each throttle position.
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