Fix P0175: Mechanic’s solutions that WORKED

code P0175 – system is too rich (Bank 2) is set when your PCM needs to cut the amount of fuel to the system to keep the stochiometric ratio at 14.7:1. That means that you either have a fault that results in dumping more fuel in the combustion process, or less air than needed.

I also did a case study of several vehicles to give you real data found in real service reports shared by mechanics who fixed that particular vehicle. Use the menu to skip to the case study, or another part:

P0175 quick overview

Meaning	P0175: System Too Rich (Bank 2)
Is it serious?	This code indicates that the engine is running too rich on Bank 2, which can lead to poor fuel economy, increased emissions, and potential engine damage if not addressed promptly.
Possible causes	-Faulty or dirty Mass Air Flow (MAF) sensor -Faulty fuel pressure regulator -Faulty or clogged fuel injectors -Leaking or stuck-open PCV valve -Faulty oxygen (O2) sensor -Issues with the Intake Air Temperature (IAT) sensor -Problems with the Engine Coolant Temperature (ECT) sensor -Faulty or dirty throttle position sensor (TPS) -Issues with the Powertrain Control Module (PCM)
How to diagnose?	Check Fuel Pressure: Ensure that the fuel pressure is within the manufacturer’s specifications at idle and under load. Inspect the fuel pressure regulator for leaks or malfunctions. Inspect the MAF Sensor: Verify the MAF sensor’s operation by checking its signal and cleaning or replacing it if necessary. Verify Sensor Operation: Use a scan tool to monitor live data from the O2, IAT, ECT, and TPS sensors to ensure they are functioning correctly. Test for Fuel System Leaks: Inspect for any fuel injector leaks or clogs, and verify that the fuel injectors are operating properly. Inspect for Vacuum Leaks: Check for any vacuum leaks, particularly in the PCV valve, which could cause incorrect air-fuel mixture readings. Examine the PCM: If all other components are functioning correctly, consider a possible PCM issue or a need for a software update.

P0172, P0175 System rich – fix case study

I thought that a faulty MAF sensor is causing only lean conditions, but apparently, it is one of the top causes for the rich system codes. And it kind of makes sense, dirty MAF will definitely cause a lean condition because there is more air coming in than it measures, but it can apparently have other faults and measure less air than is actually coming in, causing a rich condition.

The other causes were more expected, I suspect the fuel pressure regulator and other fuel system components when I see a system too rich fault code.

If you have a GM vehicle, you also need to know that I found cases of fake rich condition caused by PCM, which needed reflash at the dealership. You can verify this at your vehicle brand’s official dealer before throwing expensive parts on your car.

Here are the vehicles that participated in my study, get more insights about this code:

P0172 Volkswagen jetta

Car: 1996 Volkswagen Jetta GL 2.0L
Problem: Surge, P0172, Check engine light

Fix: The MAF sensor was contaminated by oil and the problem is fixed by replacing the MAF sensor. I would suggest first solving the oil in the intake issue because it will probably damage the new sensor as well.

Car: 1997 Volkswagen Jetta GL 2.0L
Problem: P0172, Check engine light

Fix: I found a service record from another Jetta with the same engine and the issue was exactly the same. MAF sensor was dirty of oil, only this time the cleaning was enough to resolve this trouble code.

P0172 Volvo

Car: 1998 Volvo S70 GLT 2.4L
Problem: P0172, Check engine light, P0171

Fix: This car had a very strange combination of codes, the P0172 is a system too rich, and P0171 is a system too lean. The technician checked the fuel pressure, looked for vacuum leaks, and replaced the MAF sensor and both oxygen sensors (aftermarket Denso). Turned out the car wasn’t still fixed, and the OEM oxygen sensor solved the issue.

Car: 2004 Volvo S60 2.4 2.4L
Problem: P0172, Check engine light

Fix: The car had negative fuel trims indicating the rich condition (LTFT -23%) and fuel pressure seemed to be OK (42 PSI). Further testing showed that you cannot rely on PCM to take fuel pressure readings, because the manual reading was more than 80 PSI, which is too high. Fixed by replacing the fuel pressure regulator.

P0172/P0175 Ford F-150

Car: 1999 Ford F-150 XL 4.2L
Problem: P0172, P0175, Check engine light

Fix: The fuel pressure was too high on this Ford, and the fix was simple. Replacing the fuel pressure regulator solved the trouble code.

P0172/P0175 Mercury

Car: 2003 Mercury Sable LS 3.0L
Problem: P0172, P0175, Check engine light

Fix: What should you do when you replace the fuel pressure regulator and MAF sensor and cannot find anything else? There are no vacuum/fuel leaks, injectors work fine and oxygen sensors seems to be working as well. As in this case, sometimes there is an update for your PCM which will solve the issue without replacing anything. Check at your dealership for this information.

P0172 Mazda

Car: 2002 Mazda Protege5 2.0L
Problem: P0172, Check engine light

Fix: The technician replaced the fuel pressure regulator and MAF sensor but it didn’t fix the issue. The cause was found when he did a fuel injector swap test, and the condition disappeared. Fixed by replacing fuel injectors.

P0172/P0175 Chevrolet

Car: 1996 Chevrolet Tahoe LS 5.7L
Problem: P0172, P0175, Check engine light

Fix: The technician started by measuring the fuel pressure which was slightly lower than the acceptable range so he changed the fuel pump. That fixed the fuel pressure and now it shows the right value, however, the rich condition didn’t disappear. It turned out, the fuel pressure regulator was leaking fuel into the intake. Fixed by replacing the regulator.

Car: 1996 Chevrolet K1500 Cheyenne 5.0L
Problem: P0172, P0175, Check engine light

Fix: The fuel pressure regulator is often issued on older Chevrolets having the rich condition issue. This was the same case and be careful because you might not see the regulator leaking fuel, but it does it only at certain temperatures. The problem was fixed by replacing the regulator.

P0172 Toyota

Car: Toyota Corolla CE 1.8L
Problem: P0172, Check engine light, Hesitation

Fix: This was the scan data from the vehicle: LTFT is -28.9, STFT -6.2. No vacuum leaks. MAF at idle 3.12 g/s. We often see the MAF being responsible for lean codes, but it can also trigger the rich ones if it reads too much airflow when damaged/dirty. Fixed by replacing mass airflow sensor.

P0172/P0175 GMC

Car: 1999 GMC C3500 Sierra SL 5.7L
Problem: P0172, P0175, Check engine light

Fix: Nothing was wrong with this car, it needed PCM to reflash/update specifically for triggering false rich condition codes. Engine problems are sometimes solved this way, check with the dealer if there are any updates for your vehicle’s PCM. This is common for GM vehicles.

P0172/P0175 Dodge

Car: 2000 Dodge Intrepid 2.7L
Problem: P0172, P0175, Check engine light

Fix: The technician checked the usual fuel pressure and fuel regulator which seemed to be OK. The MAF sensor was found to be covered in oil and the rich condition is fixed after cleaning the sensor. Cleaning was enough in this case, however, sometimes only the OEM part replacement will fix the issue.

P0172/P0175 Jaguar

Car: 1999 Jaguar XJ8 4.0L
Problem: P0172, P0175, Check engine light

Fix: The Vehicle was also having issues which intermittent safety power reduction and both banks’ fuel trims were highly negative, less than -20%. The vehicle is fixed by replacing the MAF sensor.

P0172 Mercedes

Car: 2005 Mercedes-Benz C230 Kompressor 1.8L
Problem: P0172, Check engine light

Fix: Data taken from the car were: idle, operating temp, upstream O2 sensor was biased at .950-.980 volt and fuel trim were negative -18.8%. The smoke machine detected a large leak in the intercooler hose. Fixed by replacing the hose.

P0172 Honda

Car: 2001 Honda Accord EX 3.0L
Problem: P0172, Check engine light, slow acceleration

Fix: Car also had the code P1121 – TP sensor signal too low. The data were TP % at WOT: 13.8% (spec: >13.7%). In D4, fast/laggy 1-2 shift, gradual acceleration. Manual 1st gear = strong power. TP volts: 0.44 – 1.2 at WOT. Car was fixed by replacing TPS (throttle position sensor).

P0172/P0175 Suzuki

Car: 2004 Suzuki Verona LX 2.5L
Problem: P0172, P0175, Hesitation, MIL Lamp on

Fix: There weren’t any vacuum leaks (shouldn’t be with rich codes) and the fuel system also seemed to be OK without out-of-spec fuel pressure or leaking fuel pressure regulator. The fix was done by replacing faulty O2 sensors.

P0172/P0175 Audi

Car: Audi A8 Quattro L 4.0L
Problem: P0172, P0175, Check engine light, Poor Idle Quality

Proccess:

1. A cold start is generally okay.
2. As the vehicle warms up, it misfires and may stall.
3. When warm, starting issues – extended cranking or failure to start.
4. The throttle becomes unresponsive after starting.
5. Pulling the oil filler cap results in a massive vacuum in the crankcase, exceeding normal levels.
6. The manometer reading shows excessive vacuum in the crankcase.
7. The oil separator underneath the inter-cooler was replaced by the dealer about a year ago.
8. Turbo diverter valves were inspected and found to be in good condition.
9. The customer reports previous PCV (Positive Crankcase Ventilation) issues.
10. Suspicions that the PCV system may be problematic again.

Fix: Both turbochargers were damaged and had to be replaced.

Conclusion

I hope my study will help you understand and solve your system to a rich condition. Just keep in mind that this is one of the codes that will require a solid diagnostic process because there are so many parts that could be causing this fault.

The good news is that you need only a simple engine code reader, a digital multimeter, and some knowledge. I hope this guide will provide you with the information you need and don’t hesitate to share your experience of solving this issue in the comment section.