Closed Loop
The ECU uses O2 sensor feedback to actively adjust fueling in real time.
Why it matters
In closed loop, the ECU self-corrects fueling errors. Problems show up as large fuel trim values rather than lean/rich conditions.
What to look for
Most driving is closed loop. WOT typically switches to open loop where fueling runs from a fixed map.
Related terms
Fueling runs from a fixed map without O2 sensor feedback, typically at WOT under boost.
The ECU's real-time, moment-to-moment adjustment to fueling. Think of it as the ECU saying "right now I need to add a little more fuel" or "right now I need to pull back a little."
The ECU's permanent, learned correction to fueling. Unlike STFT which changes moment-to-moment, LTFT is the ECU saying "over time, I've learned I consistently need to add or remove this much fuel."
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