What does a short-term fuel trim of -20 indicate?

[VanAnna]

Short-term fuel trim refers to a correction value stored in permanent memory, meaning the memory is retained even after the ignition is turned off. This value itself holds little significance as it is merely an adjustment parameter. Below is expanded information on short-term fuel trim: 1. Overview: Short-term fuel trim is a real-time correction control of fuel injection volume based on oxygen sensor feedback regarding the air-fuel mixture's richness or leanness during previous operating cycles. 2. Air-fuel mixture concentration: When the mixture is too rich (high concentration), the oxygen sensor's output voltage increases, causing the short-term fuel trim to decrease - manifested as reduced fuel injection pulse width, displaying values below 1 on diagnostic tools. Conversely, when the mixture is too lean, short-term fuel trim increases, showing values greater than 1 on diagnostic equipment.