Short-Term Fuel Trim, Bank 1

Measurement range 0-2.

The value displays how much the injection period needs to be corrected (from the preprogrammed injection period in the control module) 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 the different fuel trim adaptations (idling, lower partial load and upper partial 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 in preprogrammed in the control module 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 control module increases the injection period (to prevent a lean fuel / air mix).

Value under 1: the control module 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 (idle speed and load). When erasing the diagnostic trouble codes (DTCs), the adaptation values will be reset. This means the short-term fuel trim will be high or low when driving in the low engine speed/load ranges before the adaptations are ready.