• Troy Wierenga

Short Term vs. Long Term Fuel Trim

What's the difference between short term and long term fuel trim?



The visual...


Lets think about baseball for a minute. Let’s say the strike zone over home plate is the perfect air/fuel mix. The catcher’s arm and mitt is the short term fuel trim and where his feet are planted is the long term fuel trim. If the pitchers throw is not a strike, the catcher has to reach his arm out to catch it. Let’s say if he reaches to the left, the throw was lean, if he reaches to the right, the throw was rich. If the catcher is continuously reaching in one direction, he begins moving his feet over a little to make a prediction of the general area where he thinks the ball will be thrown.


Here is a short list of possible scenarios of short term vs. long term numbers.

  1. If long term is high, and short term is low, there has been a fairly consistent condition for a while.

  2. If long term is close to zero, but there are high short term numbers, either codes have been recently cleared and problem still exists, or a new problem has just arrived.

  3. If long term is high for 1 direction, and the short term is high in the opposite direction, either the problem is intermittent, or the problem has been fixed without clearing codes.


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