What should be confirmed if fuel trim readings are abnormal during diagnosis?

When diagnosing abnormal fuel trim readings, confirming the calibration of the mass airflow sensor is critical. The mass airflow (MAF) sensor plays a vital role in calculating the correct air-fuel mixture by measuring the amount of air entering the engine. If this sensor is miscalibrated or malfunctioning, it can provide inaccurate data to the engine control unit (ECU), leading to improper fuel trim adjustments.

Abnormal fuel trim readings indicate that the engine is not achieving an optimal air-fuel mixture, which can result in engine performance issues and increased emissions. By ensuring that the MAF sensor is calibrated correctly, technicians can ascertain that the readings reflect the true conditions of the air intake and thus adjust the fuel delivery accurately. This step is essential in the diagnostic process as it can help identify whether the issue is truly with fuel delivery or if it stems from the air measurement side of the equation.

Each of the other choices also relates to potential causes of abnormal fuel trim readings but does not address the fundamental air measurement input that significantly influences fuel trim calculations as directly as confirming the mass airflow sensor’s calibration does.