Overall drivability and vehicle performance is dependent on the engine receiving everything it needs in the right amount and at the right time. When that doesn’t happen, the Engine Control Module will try to compensate – and that typically shows up in the STFT and LTFT data PIDs you see on your scan tool. But does a correction ALWAYS indicate a “lean” or “rich” fuel condition? Or can the numbers be affected by something else? Join Pete and G. as they explore what fuel trims are, what affects them and, most importantly, how to use them in your everyday diagnostics!