On Board Diagnosis Logic

With the Air-Fuel Mixture Ratio Self-Learning Control, the actual mixture ratio can be brought closely to the theoretical mixture ratio based on the mixture ratio feedback signal from the air fuel ratio (A/F) sensor 1. The ECM calculates the necessary compensation to correct the offset between the actual and the theoretical ratios.

In case the amount of the compensation value is extremely large (the actual mixture ratio is too rich.), the ECM judges the condition as the fuel injection system malfunction and lights up the MIL (2 trip detection logic).

Fig 1: Describing A/F Sensor Signal To ECM

Courtesy of NISSAN MOTOR CO., U.S.A.

Fig 2: Identifying DTC P0172 & P0175 Conditions & Possible Causes

Courtesy of NISSAN MOTOR CO., U.S.A.