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.

A. Why Is the Right Air Fuel Ratio Important?

Your car needs the correct air fuel ratio and sparks (via spark plugs) for the perfect level of combustion to run your vehicle. And for a smooth ride, the fuel and oxygen levels need to 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. It’s set according to your car’s engine speed.

The PCM then uses readings from the heated 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, or 14:7 parts air and 1 part fuel.

B. What Triggers the P0175 Code?

Sometimes, the Engine Control Module or Powertrain Control Module may be unable to balance the air fuel ratio. This inability may be due to factors like vacuum leaks, a faulty fuel injector, or fuel delivery issues.

If the imbalance causes a rich condition (excess fuel and insufficient oxygen), the ECM registers a code P0175. This condition can also trigger a related rich code, such as code P0172.

Common Symptoms

An imbalanced airfuel mixture may trigger the P0175 code, turning your Check Engine Light on and causing severe engine and fuel economy problems.

Here are some more signs of a DTC P0175:

➤ Increased fuel consumption: 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. 

➤ Black residue from exhaust: You may find soot or black residue in your exhaust, usually due to unburnt raw fuel in the system. 

➤ Strong exhaust odors: A vehicle with a P0175 code will have a strong gasoline or diesel odor that smells like rotten eggs. This smell can also indicate a possible exhaust leak. 

➤Rough idle: Improper combustion or unburnt fuel causes your car to rough idle or misfire.

Can I Still Drive?

Symptoms like rough idle or misfiring may allow you to drive with code P0175 for some time. But if neglected, code P0175 can become very severe, leading to expensive repairs.

For example, if the fuel system runs too rich, your car may force the catalytic converter to filter out more pollutants, shortening its lifespan. Or, an improper air fuel mixture may overwork the engine, causing severe engine damage.

So it’s best to call the nearest auto repair shop to resolve the Check Engine Light and get your car fixed to avoid expensive repairs and additional replacement costs.

P0175 Causes

Several factors, such as a faulty fuel pressure sensor, a catalytic converter, or a MAF sensor malfunction, can cause DTC P0175.

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

➤ Clogged, stuck, or leaking fuel injector: This results in the fuel injector pushing extra raw fuel into the system. Leaks in the fuel system may also make it seem like the injector isn’t doing its job. 

➤Faulty fuel regulator: A faulty fuel pressure regulator will incorrectly supply excess fuel to the fuel injector. 

➤Dirty mass air flow sensor: A dirty mass air flow sensor restricts airflow and intake of oxygen, resulting in a rich condition. 

➤ Bad thermostat: This results in a rich fuel trim value as a bad thermostat can’t maintain the optimal engine temperature. 

➤Dirty or faulty oxygen sensor: An issue with the O2 sensor or AF sensor means it’ll send inaccurate oxygen readings to the ECM, prompting the fuel injector to send more fuel. 

➤ Vacuum leak: A vacuum leak lets unmonitored oxygen escape before mixing with the fuel, causing an imbalanced airfuel mixture. This leak may come from a damaged PCV hose, vacuum hose, or intake manifold gasket. 

Other causes may also include:

• Damaged fuel pump check valve
• Worn-out spark plug
• Dirty air filter
• Exhaust leak
• Bad engine coolant temperature sensor

Diagnosis for P0175

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

Your mechanic may do the following checks to diagnose 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 code p0172, are present to pinpoint the problem.

2. Afterward, they may start by inspecting the fuel pressure.

3. Your mechanic may then check if the fuel injector is blocked.

4. Next, they’ll examine the fuel injector pulse.

5. The mechanic will then check the vacuum lines for any damage or cracks.

6. They may also check if the oxygen sensor is working properly.

7. Finally, your mechanic may use a scan tool to read and compare the engine temperature to an infrared thermometer reading.

There’s a high possibility of misdiagnosis if the mechanic doesn’t compare the engine temperature to the thermometer. Subsequently,  they may also assume a component is defective without testing it properly.

Typically, analyzing short fuel trim values, long term trim values, and freeze frame data with a scan tool should help diagnose the issue properly. 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.

Possible Repairs for P0175 & Costs

Depending on the cause and diagnosis of the code P0175, your mechanic may repair or replace the following:

• Cracked or leaking vacuum lines
• Leaking intake manifold gasket
• Oxygen sensor or the AF sensor (AFR sensor)
• Mass air flow sensor
• Fuel pump
• Fuel filter 
• Fuel Injector
• Thermostat
• Air filter
• EGR valve
• Coolant temperature sensor
• Spark plugs

Repair cost:

Here are the estimated costs of some components or repairs:

• Replacing spark plug: $5-$30 per spark plug
• Cleaning MAF sensor with cleaner: $100 
• Fuel filter: $70 – $160
• Exhaust repair: $160 – $330
• Replacing MAF sensor: $80 – $380 
• EGR valve: $310 – $430
• Air-fuel sensor (AFR sensor)/Oxygen sensor: $50 – $450
• Fuel pressure regulator: $230 – $600 
• Fuel pump: $900 – $1,100
• Vacuum leak: $100 – $1,500

The replacement costs depend on which part requires repair or replacement, the vehicle’s make, location, and local labor charges.