What is P0172 code?
P0172 is a fault code set when the ECU detects that there may be too much gasoline in the engine's air-fuel mixture.
A proper air-fuel ratio of approximately 14.7:1 is vital to achieve maximum engine power and fuel economy.
Meaning of code P0172
P0172 indicates that too much gasoline has been detected in the exhaust gases leaving the combustion chamber. The ECU uses a number of instruments such as the mass air flow sensor (MAF), oxygen sensors and manifold absolute pressure (MAP) to monitor the engine's air-fuel ratio.
Most routinely, the air-fuel ratio will be measured through oxygen sensors that calculate the amount of oxygen and carbon monoxide present in the exhaust gases. The best air-fuel ratio known to modern man is 14.7:1. This particular ratio was chosen because it was discovered to have the highest power output but the lowest fuel consumption rate.
The ECU has the ability to slightly adjust the air-fuel ratio if it is rich. However, if the compensation margin is too large, a P0172 code will likely be set. The term "rich" in this case means there is too much gasoline and not enough oxygen in the engine's air-fuel ratio.
What causes code P0172?
A dirty mass air flow sensor that overestimates the amount of air entering the engine, which can cause excessive fuel delivery
A bad oxygen sensor
A leaking fuel injector allowing too much fuel into the combustion chamber
A faulty fuel regulator that is not regulating pressure to the engine as it should
vacuum leak
Possible fault in the coolant system, such as a stuck thermostat or faulty coolant temperature sensor
worn spark plugs
What are the symptoms of code P0172?
Engine malfunction light will come on
Higher fuel consumption
Black smoke coming from exhaust
How to diagnose code P0172?
By performing a fuel pressure test
Checking fuel injectors
Checking the vehicle for vacuum leaks
Inspection of Mass Air Flow Sensor and Oxygen Sensors
Checking the Air intake system for blockage
Common mistakes when diagnosing code P0172
The coolant temperature sensor and cooling system are not checked. When the engine is cold, more fuel is added to heat it to the desired temperature. If the coolant temperature sensor is not sending the correct signal, there is a possibility that the engine ECU always assumes it is running cold.
How serious is code P0172?
Vehicle may fail vehicle exhaust inspection due to code P0172 setting Check Engine Light.
If the air-fuel ratio is rich enough, black smoke that is harmful to the environment will emerge from the exhaust.
What repairs can fix code P0172?
Vacuum leak repair
Replacing a faulty fuel injector, fuel pump or fuel regulator
Replacing an overly restricted air filter
Replacing the thermostat or coolant temperature sensor
Changing spark plugs
Cleaning the oxygen sensors and mass air flow sensor
Additional information to consider regarding code P0172
It is highly recommended to check the condition of the spark plugs and the operation of the coolant temperature sensor.
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