Vehicle: 2009 Mazda Tribute, 4WD, V6-3.0L
Problem: The owner was concerned with a recent lack of power under hard acceleration onto the freeway or up steep hills. The malfunction indicator light (MIL) was not on
Case Details: The first thing the technician did was to check for diagnostic trouble codes (DTCs). There were no DTCs. Leaving the scan tool connected, he went on a test drive to duplicate the problem and to check the parameter identification data (PIDs). During test drive, he noticed bank 1 fuel trims going positive (adding fuel), while bank 2 fuel trims were going negative (subtracting fuel).
NOTE: The symptoms plus the reaction of the fuel trims indicated the possibility of a restricted exhaust system or a weak/failing fuel pump.
The technician cleared the adaptive trims and test drove the vehicle again to verify that the fuel trims behaved the same way. This time, the fuel trims on both banks went positive at all speeds and RPM ranges. When checking the PIDs, he noticed that they all looked normal except the mass airflow (MAF) sensor – the PID values were way off. When he inspected the MAF sensor, he found that it was contaminated. A bug was stuck in the sensor.
Confirmed Repair: The tech removed the bug and cleaned the MAF with a Mazda approved cleaner. After the repairs, he reset the fuel trims and went for another test drive. The fuel trims remained in the normal range and the engine’s power was restored. Problem solved!