Coming across a code P0172 essentially signals that your engine is drowning in too much fuel, a problem that wastes gas and risks damage.
Keep reading to learn more about a P0172 code, what causes it, and how you can fix it and get the correct air-fuel balance in your engine.
What Does Code P0172 Mean?
OBD-II Trouble Code P0172 Stand For “System Too Rich (Bank 1)”.
Your engine control unit is constantly monitoring and communicating with the sensors of your fuel injection system.
If the unit detects that too much fuel is in the combustion chamber, the powertrain will generate diagnostic trouble code (DTC) P0172, and in most cases, a more generic P0170 code.
There are several sensors and instruments used to detect the quantity of fuel within the exhaust gases of the chamber.
These include the manifold absolute pressure, mass air flow sensor, and the oxygen sensors. Whenever there is too much fuel, that means there is not enough oxygen.
The term “Bank 1” refers to the area of the engine that has the first cylinder, which is technically cylinder #1. The oxygen sensors measure the quantity of oxygen in the exhaust gases that are in this cylinder.
If the sensors detect that there is very little oxygen present, it means the ratio of air-to-fuel is not where it needs to be.
The normal ratio is 14.7:1 for most gasoline engines. This ensures the engine generates the most amount of power possible with the least amount of fuel.
If the engine control unit detects the bank 1 cylinder is “too rich,” it means it has too much fuel and not enough in oxygen.
Symptoms of Code P0172
The symptoms of trouble code P0172 are usually the same symptoms of an engine running rich. Normally, your check engine light will be on (unless the bulb is burnt out). But in addition to that, here are some additional symptoms:
- Strong fuel or rotten egg smell from exhaust
- Poor fuel economy
- Engine hesitating
- Engine misfiring
- Lack of power when accelerating
- Rough idling
Causes of Code P0172
There are several reasons why this problem could exist. The most common reasons include a faulty oxygen sensor or a dirty mass air flow sensor (MAF). In addition, here are some additional causes of throwing code PO172.
- Faulty fuel injectors leaking fuel into the combustion chamber
- Faulty spark plugs
- Faulty manifold absolute pressure sensor (MAP)
- Faulty throttle position sensor
- Dirty or clogged air filter
- Vacuum leak
- Faulty ECU (or PCM module)
- Faulty fuel pressure regulator
- Faulty thermostat (stuck open)
- Cooling system that’s been retrofitted (ie: thermostat removed, fan running direct, etc.)
- Restricted or damaged fuel line
How to Fix
Because there can be so many causes of DTC P0172, diagnosing and ultimately fixing the issue can be tricky. It’s recommended to always start with the easiest options.
Check and clean your Mass Air Flow sensor and air filter first and work your way down from the easiest (and cheapest) possible causes.
It’s common for some to automatically assume they need to replace either the O2 sensor or air/fuel sensor but this is a common misdiagnosis.
Cost to Fix Code P0172
Fuel Injector – Replacing a fuel injector can cost between $130-$500. The labor cost is typically around $80-$140 per hour. It might take 1 to 3 hours to complete the job, depending on your vehicle’s make and model.
Spark Plug – The cost of a spark plug replacement ranges from $50-$300. This price depends on the type of spark plug and labor rates. A spark plug change usually takes less than an hour.
MAP Sensor – A new MAP sensor can cost $50-$300. The labor cost for replacing the MAP sensor is usually between $80 and $140 per hour, and the replacement process generally takes under an hour.
Throttle Position Sensor – Replacing your throttle position sensor can cost anywhere from $100-$300. The labor for this job will range from $80 to $140 per hour. The entire process should take about an hour.
Air Filter – An air filter replacement costs around $15-$100, depending on your car and the type of filter. The labor cost for this task is minimal and typically included in the price. It usually takes less than half an hour.
ECM/PCM – Repairing or replacing your vehicle’s ECM or PCM costs between $500-$2,000. The labor cost is generally $80 to $140 per hour. Total replacement time can range from 1 to 4 hours, sometimes more.
Fuel Pressure Regulator – The cost of a fuel pressure regulator ranges from $50 to $200. Labor costs for the replacement are about $80-$140 per hour. The replacement process usually takes under an hour.
Thermostat – Replacing a thermostat costs between $50 and $200 for parts and labor. It typically takes between 30 minutes to 2 hours to complete the job.
Fuel Line – A fuel line repair or replacement can cost around $100-$600. The labor rate for this service ranges from $80 to $140 per hour. The job might take anywhere from 1 to 4 hours, depending on the complexity.