What is fuel trim, and how does a positive fuel trim manifest during engine operation?

• A. Fuel trim reflects ECU adjustments to fuel delivery to reach the stoichiometric air-fuel ratio; a positive trim means the ECU is adding fuel.
• B. Fuel trim is a fixed ambient reading used for sensor calibration; positive trim means shutting off fuel.
• C. Fuel trim is the sum of all injector voltages; positive trim means the engine is turbocharged.
• D. Fuel trim indicates fuel pressure only; positive trim means reduced pressure.

Answer: (A)