P0172 code definition
P0172 is a fault code that is set when the ECU detects that there may be too much gasoline in the engine’s air-fuel mixture.
A correct air/fuel ratio of about 14.7:1 is essential for maximum engine power and fuel economy.
What the P0172 code means
The P0172 code indicates that too much gasoline has been detected in the exhaust gas leaving the combustion chamber. The ECU uses various instruments such as the mass air flow (MAF) sensor, oxygen sensors, and manifold absolute pressure (MAP) to monitor the engine’s air/fuel ratio.
The most common air/fuel ratio is measured by oxygen sensors, which calculate the amount of oxygen and carbon monoxide present in the exhaust. The best known air/fuel ratio today is 14.7:1. This particular ratio was chosen because it was found to have the highest power but the lowest fuel consumption ratio.
The ECU has the ability to adjust the air/fuel ratio slightly, if it is rich. However, if the offset margin is too large, code P0172 is likely to be set. The term “rich” in this case means that there is too much gasoline and too little oxygen in the engine’s air/fuel ratio.
What causes the P0172 code?
- A contaminated mass airflow sensor that overestimates the amount of air entering the engine, which can cause excessive fuel delivery.
- Bad oxygen sensor
- Leaking fuel injector allowing too much fuel to enter the combustion chamber
- Faulty fuel regulator, which may not regulate the fuel pressure to the engine as it should.
- Vacuum leakage
- Possible cooling system malfunction, such as a clogged thermostat or a defective coolant temperature sensor
- Worn-out spark plugs
What are the symptoms of the P0172 code?
- The check engine light is on
- Increased fuel consumption
- Black smoke coming out of the exhaust
How does a mechanic diagnose a P0172 code?
- Performing a fuel pressure check
- Using noid lights to check fuel injector pulses
- Checking the vehicle for vacuum leaks
- Checking the air mass flow meter and oxygen sensors
- Checking the air intake system for clogging
The most common errors when diagnosing code P0172
The technician may not have checked the coolant temperature sensor and the cooling system. When the engine is cold, more fuel is added to help warm the engine to the desired temperature. If the coolant temperature sensor is not sending the correct signal, there is a possibility that the engine ECU is assuming that it is always cold.
How serious is the code P0172?
- The car may miss a state vehicle inspection because the P0172 code causes the Check Engine Light to turn on.
- If the air/fuel ratio is rich enough, black smog comes out of the exhaust, which is harmful to the environment.
What fixes can repair a P0172 code?
- Repair a vacuum leak
- Replacing a defective fuel injector, fuel pump, or fuel regulator
- Replacing an overly restricted air filter
- Replacement of a defective thermostat or coolant temperature sensor
- Replacement of spark plugs
- Clean oxygen sensor and mass airflow sensor.
Additional notes on code P0172
It is recommended to check the condition of the spark plugs and the operation of the coolant temperature sensor.
