Short Term Fuel Trim

percent. A positive fuel trim value indicates that the PCM is adding fuel in order to compensate for a lean condition. A negative fuel trim value indicates that the PCM is reducing the amount of fuel in order to compensate for a rich condition.

When the PCM determines that the short term fuel trim is out of the operating range, the following DTCs will set:
^ DTC P0171 Bank 1 Too Lean
^ DTC P0172 Bank 1 Too Rich