Short-term fuel trim, bank x

Measurement range 0-2.

The value displays how much the injection period needs to be corrected (from the pre-programmed injection period in the engine control module (ECM)) to reach λ=1. If the engine runs lean or rich (λ deviates from 1), the short-term fuel trim injection period is increased or decreased so that λ=1. The average value of this parameter from different engine speed and load ranges is used for in the different fuel trim adaptations (idling, lower part load and upper part load) so that the short-term fuel trim is always around 1.

Short-term fuel trim = the actual injection period required to reach λ=1, divided by (/) the injection period pre-programmed in the engine control module (ECM) to reach λ=1.

The normal value oscillates around 1, when the lambda adaptations for each engine speed (RPM) / load range are ready.

Value over 1: The engine control module (ECM) increases the injection period (to prevent a lean fuel / air mix).

Value under 1: The engine control module (ECM) decreases the injection period (to prevent a rich fuel / air mix).

The parameter must be checked under stable conditions, such as stable engine speed (RPM) and load.

HINT: When λ deviates from 1, the short-term fuel trim initially compensates at every engine speed (RPM) / load range (idling speed, lower partial load and upper partial load). The diagnostic trouble codes (DTCs) are erased, the adaptation values are reset. This means short-term fuel trim will be high or low when driving in the low engine speed/load ranges before the adaptations are ready. For more information about fuel-trim adaptation, see VADIS Design and Function, Fuel trim.