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P0175 OBD2 Code: System Too Rich (Bank 2)

When the air-to-fuel ratio in your engine is off, the OBD2 Code P0175 will tell you.
P0175 Code shows you the air-to-fuel ratio in your engine is off.

The P0175 OBD2 code tells you the air-to-fuel ratio in your engine is off. Specifically, there’s more fuel in the mix than there should be. This decreases your fuel economy, increases your emission, and can cause internal engine damage if not fixed promptly. 

There are a lot of different engine problems that could lead to a rich air/fuel mixture. Identifying the exact source of the P0175 trouble code is much easier if you’re able to read other diagnostic trouble codes, especially those related to the oxygen sensors, MAF sensor, or fuel pressure. 

It’s also a good idea to look up technical service bulletins related to this code for your vehicle. While it is a generic powertrain code, and therefore applicable to any OBD2-compatible vehicle, the most common causes and fixes may differ between manufacturers. Learning what has fixed the problem for other owners of your vehicle could steer you toward the correct solution for yours.

P0175 Code Definition (Generic)

System too rich (Bank 2)

What does P0175 mean?

The ideal air to fuel ratio for a combustion engine is 14.7:1, or 14.7 parts air to every 1 part fuel. Variations from this standard are described with the words “rich” and “lean.”  A lean mixture has more air than it should, while a rich mixture has more fuel than the ideal ratio. 

The powertrain control module (PCM) or engine control module (ECM) periodically tests the air/fuel mix and makes adjustments to maintain this ideal 14.7:1 ratio. In the case of a rich mixture, less fuel is injected into the mixture to compensate for the rich condition. 

If the adjustments made by the PCM or ECM in response to the rich condition exceed a designated level, the P0175 trouble code is triggered. It may also trigger at the point that the ECM or PCM is unable to fully compensate for the rich mixture. 

Maintaining the correct air-to-fuel ratio is important maintaining proper engine timing. The amount of air and gasoline within each cylinder dictates the speed and timing of the corresponding piston. Even a slight imbalance can disrupt this timing, causing misfires and other engine issues. 

This code doesn’t tell you the exact cause of the rich condition, only that it exists, something that can make it tricky to fully diagnose. Your OBD2 scanner is often your best friend in making these diagnoses accurately, since you’ll often see P0175 in combination with one or more other trouble codes. 

What are the symptoms of the P0175 code?

In some cases, you won’t notice any drivability symptoms when the P0175 trouble code is active. The most common symptoms include:

  • Activation of the check engine light
  • Reduced engine power
  • Increased fuel consumption
  • Rough idling
  • Hesitations from the engine
  • Fuel smell in exhaust
  • Soot or black smoke in exhaust
  • Engine misfires

What are the causes of P0175?

  • Dirty or faulty mass air flow (MAF) sensor
  • Over-oiled air filter
  • Leaks in vacuum lines
  • Dirty or faulty oxygen sensor
  • Faulty air/fuel ratio sensor
  • Faulty coolant temperature sensor or coolant thermostat
  • Fuel injectors are leaking, stuck, or clogged
  • Fuel pressure regulator is stuck or faulty
  • Worn spark plugs

How serious is the P0175 code?

The P0175 trouble code is of moderate severity. It is safe to drive with this code active for a short period of time. However, long-term operation with a rich fuel mixture can lead to more serious damage to internal engine components. For that reason, you should make repairs as soon as possible. 

How to diagnose and fix the P0175 code

Tools you’ll need:

  • OBD2 scan tool
  • Basic tools (screwdriver, pliers, etc.)
  • Fuel pressure gauge
  • MAF sensor cleaner
  • Digital multimeter
  1. Use an OBD2 scanner to read all trouble codes. If other codes are present address those first, as they may be the cause of the rich fuel condition.
  2. Check for obstructions in the airflow into the engine. Inspect the air filter, as well, to make sure it’s not clogged or dirty. 
  3. Visually inspect all vacuum hoses for leaks and damage. Pay special attention to the ends of hoses, which can become cracked or damage. Replace as necessary. 
  4. If you use an oiled air filter, check to make sure that it’s not over-oiled. If you see traces of oil on the MAF sensor, clean the sensor and change to a non-oiled filter. 
  5. Remove the MAF sensor and clean it using MAF sensor cleaner. Once it’s reinstalled, clear all trouble codes, test drive your vehicle, and re-scan to see if the P0175 OBD2 code returns.
  6. Inspect the fuel lines, checking for any cracks or pinches that could be affecting the flow of fuel. Repair or replace as necessary. 
  7. Use a fuel pressure gauge to test your vehicle’s fuel pressure. If there are issues with the fuel pressure, inspect the fuel injectors and fuel pressure regulator. Either of these components can become stuck, leading to high fuel pressure that causes the rich condition. Faulty or leaking fuel injectors can also release too much fuel into the cylinders, resulting in a rich fuel mix. Clean or replace components as necessary.
  8. Check the operation of the coolant temperature sensor, MAF sensor, and oxygen sensors using a digital multimeter, and replace as necessary. 
  9. If the code still won’t clear at this point, it’s recommended to take your vehicle to a mechanic for further diagnosis. You could have a problem with the cooling system, or require reprogramming of your ECM or PCM. Professional garages have the diagnostic equipment to determine if this is the case.

Common mistakes to avoid while diagnosing the P0175 code

Make sure you follow the entire diagnostic process when you’re working with a P0175 code. Because there can be a number of different causes of a rich fuel condition, the obvious answer isn’t always the right one. If you rush the diagnosis, you could easily end up replacing the MAF sensor when the real problem is a vacuum leak. 

Tips to avoid P0175 in the future

Make sure you don’t over-oil engine components when you install them. If this grease gets onto your MAF sensor or oxygen sensors, it can cause faulty readings and malfunctions, leading to codes like P0175.

Read more: Best OBD2 Scanner: Complete Buying Guide and Review 2020

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