Circuit Description

WARNING: This page is about a different car, the 2003 Toyota Matrix and 2003 Toyota Corolla. However, it is still accessible from the selected car via links, so may be relevant.

Fuel trim refers to feedback compensation value compared against basic injection time. Fuel trim includes short-term fuel trim and long-term fuel trim. Short-term fuel trim is short-term fuel compensation used to maintain air-fuel ratio at it's ideal theoretical value. Signal from heated oxygen sensor indicates whether air-fuel ratio is RICH or LEAN compared to ideal theoretical value, triggering a reduction in fuel volume if air-fuel ratio is rich, and an increase in fuel volume if it is lean.

Long-term fuel trim is overall fuel compensation carried out long-term to compensate for continual deviation of short-term fuel trim from central value due to individual engine differences, wear over time and changes in usage environment. If both short-term fuel trim and long-term fuel trim are LEAN or RICH beyond a certain value, it is detected as a malfunction and Malfunction Indicator Light (MIL) lights up.

Detecting condition of DTCs is when air-fuel ratio feedback is stable after engine warming up, fuel trim is considerably in error on RICH (P0171) or LEAN (P0172) side (2 trip detection logic). If total of short-term fuel trim value and long-term fuel trim value is within plus or minus 25%, system is functioning normally.