Solve driveability issues with fuel trim diagnostics Fuel trim is an indicating metric that can shed light on how hard the engine controller is working to achieve its desired air-to-fuel ratio. By Scott Brown, Technical Editor F uel trim is a vital data point technicians can leverage when assessing vehicle anomalies related to driveability and emissions challenges. Fuel trim (also known as additive, block learn, integrator, or multiplicative) is the correction factor applied to the air-fuel mass delivered to the cylinder during engine operation. Small errors in this cylinder air/fuelhttp://www.VehicleServicePros.com