Fuel trim is being discussed. Technician A says a positive fuel-trim value means the PCM detects a lean mixture and is increasing the pulse width to add more fuel to the mixture. Technician B says LTFT [long-term fuel trim] is erased when the ignition is turned off. Who is correct?
A)A only
B)B only
C)both A and B
D)neither A nor B

Question

Quizplus · Accepted Answer

Technician A is correct because a positive fuel trim value indicates the Powertrain Control Module (PCM) is compensating for a lean condition by adding more fuel. Technician B is incorrect because LTFT values are stored in the PCM's memory and are not erased when the ignition is turned off; they are long-term adjustments.

Fuel Trim Is Being Discussed