P0175: System Too Rich (Bank 2)

What Is P0175?

The P0175 code is a generic OBD-II Diagnostic Trouble Code (DTC) defined as “System Too Rich (Bank 2)”.

It shows up when the Engine Control Module (ECM) or Powertrain Control Module (PCM) detects too much fuel or insufficient oxygen in the air-fuel ratio. This creates rich mixture conditions (excess fuel and inadequate oxygen). 

A. Why Is the Right Air-Fuel Ratio Important?

Your car needs the correct air-fuel ratio and spark (via spark plugs) for the perfect combustion to run your vehicle. And for a smooth ride, the fuel and oxygen levels must change as you slow down or rev up your engine.

The ECM or PCM sets the required air-fuel ratio using the information sent by the mass air flow sensor (MAF sensor), crankshaft position sensor, and engine coolant temperature sensor. 

The PCM then uses readings from the oxygen sensor (O2 sensor) to further adjust the air-fuel ratio based on oxygen levels in the exhaust gas.

Ideally, your vehicle’s air-fuel mixture ratio should be 14:7:1, i.e., 14:7 parts air and 1 part fuel.

B. What Triggers the P0175 Code?

Sometimes, the ECM or PCM may be unable to balance the air-fuel ratio due to vacuum leaks, a faulty fuel injector, or other fuel delivery issues.

If the imbalance causes a rich condition, the ECM registers a code P0175. This can also trigger a related code P0172, defined as “System Too Rich (Bank 1)”.

P0175 Causes

A faulty fuel pressure sensor, damaged catalytic converter, or malfunctioning MAF sensor can be the possible cause of DTC P0175.

Here’s why these components may trigger the P0175 error code:

➤ Clogged, stuck, or leaking fuel injector: Sometimes, a faulty fuel injector pushes extra fuel into the system. Leaks in the fuel system may also make it seem like the injector isn’t doing its job. 

➤ Faulty fuel pressure regulator: A malfunctioning fuel pressure regulator will supply excess fuel to the fuel injector, causing an imbalance in the air-fuel ratio. 

➤ Dirty mass air flow sensor: A dirty MAF sensor is another common cause that restricts oxygen intake, resulting in a rich condition. 

➤ Bad thermostat: If the thermostat is stuck open, it prevents the engine from warming up properly, keeping the engine too cool. As a cold engine needs more fuel, the system injects excess fuel, leading to a rich fuel mixture.

➤ Dirty or faulty oxygen sensors: A failing O2 sensor or AF (air-fuel) sensor will send inaccurate oxygen readings to the ECM. Any incorrect sensor reading will prompt the fuel injector to push more fuel. 

➤ Vacuum leak: A vacuum leak lets unmonitored air into the engine’s intake system, creating an incorrect air-fuel mixture with excess air. To compensate for the unmetered air, the ECU injects more fuel, leading to a rich condition. 

Other underlying causes include:

• Damaged fuel pump check valve
• Worn-out spark plug
• Dirty air filter
• Exhaust leak
• Faulty coolant temperature sensor
• Over-reporting manifold absolute pressure (MAP) sensor
• Shorted fuel injector windings
• Outdated Engine Control Module (ECM) or PCM

6 Major Symptoms of DTC P0175

An incorrect air-fuel mixture may trigger the P0175 code, turning your Check Engine Light (CEL) on.

Here are some other signs of a DTC P0175:

1. Black residue from exhaust: You may find soot or black residue in your exhaust, usually due to unburnt raw fuel in the system. This also causes increased emissions. 
2. Strong exhaust odors: Vehicles with a P0175 error code will emit a strong gasoline or diesel odor due to the presence of excess, unburnt fuel. This smell can also indicate a possible exhaust leak. 

   NOTE: Faulty oxygen sensors may also cause the odor.

3. Rough idle or misfires: An overly rich fuel mixture will disrupt the combustion process, leading to rough idle, misfires, and uneven engine operation. 
4. Sluggish acceleration: Excess fuel can cause inefficient combustion, leading to decreased engine performance and poor acceleration. 
5. Poor fuel economy: Fuel consumption increases when your vehicle releases unburnt fuel from your tailpipe. A faulty fuel injector could also inject more fuel, leading to high fuel consumption. 
6. Engine oil dilution: Unburnt fuel can seep into the engine oil, reducing its lubrication properties and potentially causing engine wear or damage.

Can You Still Drive?

Symptoms like rough idling or misfiring may allow you to drive with code P0175 for some time, but it’s not recommended. If neglected, code P0175 can become severe, leading to expensive repairs.

For example, if the fuel system runs too rich, your car may force the catalytic converter to filter more pollutants, stressing it and shortening its lifespan. An improper air-fuel mixture may also overwork the engine, causing severe internal damage.

So, it’s best to call an auto repair shop ASAP to get the code and underlying reason fixed.

Diagnosis for P0175

If you misdiagnose code P0175, you may replace the wrong parts to resolve the error code. So, it’s best to contact a professional mechanic.

Your mechanic may do the following checks for diagnosing the P0175 trouble code:

1. Use an OBD-II scanner to determine if the P0175 rich code is causing issues. They’ll also check if other codes, such as error code P0172, are present. 
2. Analyze short–term fuel-trim values, long–term trim values, and freeze frame data on the scan tool to check for rich conditions. The short–term fuel trim values are the real-time adjustments made by the ECM or PCM to your car’s air-fuel mix, while long-term fuel trim values are the cumulative adjustments made to the air-fuel mix over time. 
3. Inspect for incorrect fuel pressure, which could be caused by a faulty fuel regulator. 
4. Check for a blocked or leaking fuel injector. 
5. Examine the fuel injector pulse. 
6. Check the vacuum lines for any damage or cracks. 
7. Check if the oxygen sensor and mass airflow sensor are relaying an incorrect reading. 
8. Finally, use the scan tool to read and compare the engine temperature to an infrared thermometer reading. This will help rule out a malfunctioning thermostat.

Possible Repairs for P0175 & Costs

Here are the potential repairs for DTC P0175 and their estimated costs (including labor charges):

• Cleaning MAF sensor: $85 – $125
• Air filter: $10 – $25
• Intake manifold gasket replacement: $260 – $1,800
• Fuel filter replacement: $190 – $280
• Fuel injector replacement: $335 – $2,000
• Replacing fuel lines: $150 – $2,000
• Fuel pressure regulator replacement: $260 to $870 
• Fuel pump replacement: $1,100 – $1,300
• Replacing spark plugs:
  • Copper spark plugs: $2 to $10 per piece
  • Silver spark plugs: $5 per piece
  • Platinum spark plugs: $10 per piece
  • Double platinum spark plugs: $20 per piece
  • Iridium spark plugs: $20 to $100 per piece
• MAF sensor replacement: $250 – $470 
• MAP sensor replacement: $60 – $170 
• Faulty coolant temperature sensor replacement: $400 – $500
• Oxygen sensor replacement: $360 – $520 
• Exhaust pipe replacement: $1,130 – $1,170
• EGR valve replacement: $135 – $520
• Thermostat replacement: $200 – $750
• Vacuum leak (or replacing vacuum lines): $100 – $1,500
• ECM replacement: $1,030 – $1,110

NOTE: The replacement costs depend on your vehicle’s make, your location, and local labor charges.