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My car sprung a P0101 pending code recently, which shows up as a Mass or Volume Air Flow Sensor "A" Circuit Range/Performance on my BlueDriver OBDII scanner. I started to read this article SUCCESSFUL MAF SENSOR DIAGNOSIS by Sam Bell and I couldn't follow this discussion that uses the terms open-loop and closed-loop. What exactly is this referring to and how can I trigger each in my vehicle?

To function correctly, all of the air entering an engine's combustion chambers must be "seen" by the MAF sensor. This means that any vacuum or air leak downstream of the sensor will result in insufficient fuel metering, causing a lean condition in open-loop operation and higher-than-normal fuel trim values in closed-loop.

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    Open and closed loop are control algorithms usually coded in the ecu - but to solve your problems apply the tests and look at the results, the code and meaning you show suggest a replacement sensor is required. – Solar Mike Sep 27 '17 at 5:21
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The engine runs in "open loop" when first started, before the oxygen sensors come up to operating temperature. It basically means the fuel is being metered with MAP/MAF as the primary input.

Once warmed up, fuel is metered by an active feedback loop with the O2 sensor, known as closed-loop operation.

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Open and closed loop are control algorithms usually coded in the ecu - but to solve your problems apply the tests and look at the results, the code and meaning you show suggest a replacement sensor is required.

The trim values can usually be used, if they are editable, to "fine tune" the sensor in the application - perhaps due to parameters such as pipe length etc.

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Trim levels generally refer to fuel trims. St and lt. Short term and long term. They are essentially the correction factors introduced following a combustion cycle reading. At the o2 sensor. You have air. fuel. spark. and the o2's detect the remaining fuel/oxygen mixture. This generates a correction; short term and long term. If your able to log those values huge corrections like over 5% ST is ideal. And maybe up TO 20% long term. All this is in a traditional internal combustion engine. Not turbo\ supercharged ,nitrous or hybrid. Though principles are standards. It really matters what vehicle we are talking about. Hope that helps a bit.

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