DTC Detection 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 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 lean), the ECM judges the condition as the fuel injection system malfunction and illuminates the MIL (2 trip detection logic).

Sensor

Input signal to ECM

ECM function

Actuator

A/F sensor 1

Density of oxygen in exhaust gas

(Mixture ratio feedback signal)

Fuel injection control

Fuel injector

DTC No.

Trouble diagnosis name

(Trouble diagnosis content)

DTC detecting condition

Possible cause

P0171

FUEL SYS-LEAN-B1

[Fuel injection system too lean (bank 1)]

Fuel injection system does not operate properly.
The amount of mixture ratio compensation is too large. (The mixture ratio is too lean.)

Intake air leakage
A/F sensor 1
Fuel injector
Exhaust gas leakage
Incorrect fuel pressure
Lack of fuel
Mass air flow sensor
Incorrect PCV hose connection

P0174

FUEL SYS-LEAN-B2

[Fuel injection system too lean (bank 2)]