Autos: fuel trim

Self-tutoring about autos: the tutor mentions the idea of fuel trim.

To my understanding, fuel trim means the amount of fuel the computer decides to add or subtract from the default amount. Short-term fuel trim refers to instantaneous execution, while long-term measures a trend. Positive means fuel is being added to default; negative, subtracted. Fuel trims are decided based on feedback taken from the exhaust side.

Fuel trim readings show up on some car computer readers.

Source:

gtc.ca