Function Explanation (DTC Detection Outline)

The PCM detects the oxygen concentration in the exhaust gas from the A/F sensor signal and performs fuel injection amount feedback to maintain the optimum air/fuel ratio. If a condition in which the feedback correction amount is large (fuel injection amount being increased) continues for the specified time, a feedback correction amount malfunction is determined, and a DTC is stored. The feedback correction amount has a "Fuel feedback correction amount" for the air/fuel ratio and a "Fuel learning correction amount" for fuel injector deterioration over time.
"Fuel feedback correction amount (SHRTFT1)" and "Fuel learning correction amount (LONGFT1)" can be verified from the M-MDS PID item.

The sum of the fuel feedback correction amount (SHRTFT1) and the fuel learning correction amount (LONGFT1) is the specified value (30 % ) or more, and 10 s or more have elapsed with the fuel learning correction amount (LONGFT1) at the specified value (15 % ) or more.

Fig 1: Fuel Feedback Correction Amount Waveform (SHRTFT1)
Courtesy of MAZDA MOTORS CORP.
Fuel learning correction amount (LONGFT1) at specified value (25%) or more.

Fig 2: Fuel Feedback Correction Amount Waveform (LONGFT1)
Courtesy of MAZDA MOTORS CORP.