What Is Open Loop?
Open loop is the operating mode in which the engine computer meters fuel from pre-programmed maps, ignoring oxygen-sensor feedback. It occurs normally at cold start and warm-up, and under heavy load on some strategies.
In plain English
When an engine starts cold, its oxygen sensors are too cool to signal accurately, so the computer runs on its stored calibrations — richer mixtures, fixed timing — until everything reaches operating temperature. Then it transitions to closed loop.
Open loop is normal at cold start. It's a problem only when a warmed engine stays in open loop — usually a temperature sensor, oxygen sensor, or heater circuit fault — because fueling accuracy and self-testing both depend on closed-loop feedback.
Example
Related trouble codes
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