P0172 obd2 code description and its analysis on engine fuel system

To check P0172 obd2 code the engine fuel mixture has to be monitored by measuring the oxygen sensor signal voltage readings at both idle and high idle settings.

P0172 Fuel mixture System

This obd2 P0172 code refers to the engine fuel mixture which is too rich. This can be checked by testing the oxygen sensor in the engine bank 1 exhaust manifold. If accessible, the oxygen sensor can be tested for voltage while the engine is running. If running rich, here are some possibilities:

oxygen sensor diagram

defective oxygen sensor
defective mass sensor (service it first)
engine vacuum leak
Bad wiring connections or ground

How fuel mixture affects your engine:

In an engine condition where the air-fuel mixture is rich and too few O2 (oxygen) in the engine exhaust, the oxygen levels across the sensor internal element which generates a voltage through the sensor at around 0.8 to 0.9 volt. However, when the air/fuel mixture is lean, and the sensor's voltage decrease to 0.1 to 0.3 volt. (note: readings will alway be under 1 volt range). This shows that when the voltage reading at the sensor is high, the air mixture is rich whereas if the voltage reading is low, it is lean. For the mixture to be normal, the sensor voltage should oscillate between 0.1 and 0.9 volt.

The ECM (engine computer) uses the engine mixture data to adjust the fuel setting and engine ignition timing as the engine is warming up. If the coolant sensor has a defect and tells the computer otherwise that it is hot, the resulting fuel mixture will be rich because the ecm is compensating. Such term as closed loop is used to describe the operating cycle when all engine control sensors are used to get best fuel engine mixture that has the lowest emissions and good horsepower. And when an engine is operated in open loop cycle, it runs rich accompanied by more exhaust emissions. The quicker the engine attains close loop cycle and remains in that state, the better performance is obtained without sacrificing the environment.



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