P0172 – Meaning, Causes, Symptoms, & Fixes
Code P0172 Definition
Bank 1 has more fuel then it should or not enough air.
What Does P0172 Mean?
Combustion engines run most efficiently when they maintain an air-fuel mixture ratio of 14.7 parts air to 1 part fuel. When the upstream oxygen sensor detects there are less than 14.7 parts air to 1 part fuel in the air-fuel mixture, a rich condition exists. To keep the engine running properly, the powertrain control module (PCM) tries to compensate for the rich condition by injecting less fuel to the mixture in an effort to maintain the proper 14.7:1 air-fuel ratio. When these adjustments become too large, code P0172 is triggered.
What Are the Symptoms Of P0172?
- Check Engine Light is on
- Lack of power from the engine
- Rough idle
- Engine hesitating
- Engine misfiring
- Strong fuel smell from exhaust
What Is The Cause Of P0172?
- Dirty or faulty Mass Air Flow (MAF) sensor
- Faulty oxygen sensor
- Faulty air-fuel ratio Sensor
- Leaky fuel injectors allowing too much fuel into the combustion cylinders
- Worn spark plugs
- Stuck fuel pressure regulator
- Faulty coolant temperature sensor
- Faulty coolant thermostat
How Serious Is Code P0172? – Moderate
It is okay to drive a vehicle with P0172 for a short period of time, but driving with this code for an extended period of time can cause internal engine damage and failure of the catalytic converter.
Code P0172 Common Diagnosis Mistakes
It is important to complete the entire diagnostic process when diagnosing P0172. Many people will replace the air-fuel sensor or O2 sensor as soon as they get a bad reading, but the root cause is often a dirty or faulty Mass Air Flow (MAF) Sensor or vacuum leak, thus causing the O2 or A/F sensor to read differently to compensate. Reading and analyzing fuel trims and the freeze frame data is the key to properly diagnosing P0172.
Tools Needed to Diagnosis Code P0172:
How To Diagnosis Code P0172?
Difficulty of Diagnosis and Repair – 3 out of 5
- Use FIXD to scan your vehicle to verify P0172 is the only code present. If other codes are present, they must be addressed first.
- Inspect your air intake box and air intake pipe for any obstructions that would prevent sufficient airflow in the engine. Inspect your air filter to ensure it is not dirty and it is seated properly.
- Remove the Mass Air Flow (MAF) Sensor and clean the sensor using mass air flow cleaner. Reinstall the Mass Air Flow (MAF) Sensor and clear the check engine light using FIXD. If the check engine light comes back on with code P0172 continue the diagnostic process.
- If check engine light code P0172 persists after you have inspected the air intake system and cleaned the Mass Air Flow (MAF) Sensor, perform a fuel pressure test. If any components in the fuel system are failing, replace them as necessary. Pay special attention to the fuel pressure regulator and the fuel injectors. If the fuel pressure regulator is stuck, it can cause a rich condition due to the high pressure. If the fuel injectors are faulty, they could leak fuel into the cylinders rather than delivering the precise amount needed for the air-fuel ratio.
- Check that your coolant temperature sensor and coolant thermostat are functioning properly (see steps 3 and 4 of P0128). If either of these is not functioning properly, the vehicle will stay in an “open-loop” operation and continue to deliver a fixed rich mixture.
- If the check engine light persists after this diagnostic process, it is most likely time to change the oxygen sensor(s) and/or A/F sensor. You can test the oxygen sensor to verify this is the fix. Here is a great video that clearly explains this process!
Estimated Cost of Repair
For error code P0172, one or more of the below repairs may be needed to solve the underlying issue. For each possible repair, the estimated cost of repair includes the cost of the relevant parts and the cost of labor required to make the repair.
- Air filter $20
- Clean MAF $100
- Fuel pressure regulator $200-$400
- Air fuel sensor or oxygen sensor $200-$300
- Thermostat $200-$300
- Engine coolant temperature sensor $150-$200