Error Code P0175 is defined as Engine Too Rich Bank 2. As its definition suggests, this code describes a rich condition problem (exhaust with too little oxygen) on O2 (oxygen) sensor Bank 2. For vehicles on V6, V8 or V10 engines, the Bank 2 is located at the side of the engine without cylinder #1.

This code is a generic trouble code, meaning it applies and appears to all vehicles equipped with OBD-II. Specifications on the definition, troubleshooting and repair of course, vary from one make or model to another.

Definition

The engine needs to put in the right amount of fuel for the right amount of air that gets in. The proper AFR or air-fuel ratio is needed in order to deliver the best power and fuel economy for the engine. The PCM uses multiple sensors such as MAF (mass airflow), CKP (crankshaft position), and ECT (engine coolant temperature) to read and determine how much fuel it should put in. Through the feedback from the heated oxygen (HO2S) sensor or AFR sensor, or Lambda sensor, the PCM will fine-tune the fuel injector pulse width to be able to deliver the best air-fuel ratio.

By definition, Error Code P0175 indicates the PCM (powertrain control module, also referred as ECM or engine control module) has detected too much fuel and not enough oxygen in the air fuel ratio. This code is set when the PCM is unable to compensate for the amount of air or fuel required to get back to the required air fuel ratio. This also means that there is too much fuel being injected, causing the engine to take more than fuel it is required to consume. The PCM will try to compensate the difference by reducing IPW, but if the trim goes more than -25% or so, the PCM will detect it as a malfunction, setting the trouble code.

Note that this code is similar to P0172; some vehicles may even show both codes simultaneously.

Common Symptoms

Symptoms for this error code may vary depending on the nature it was set, and the accompanying error codes. It usually doesn’t cause drivability issues. As with other trouble codes, it triggers the Check Engine light, and at the very least, it causes excessive fuel consumption as the PCM is set at “limp-home mode” and no longer for HO2S and AFR sensors for their feedback. Other common symptoms include:

  • Black residue or soot from the exhaust
  • Strong odor from the exhaust
  • Misfiring of the engine
  • Lack of power on acceleration (on other cases)
  • Trouble idling when warm or when sitting at a stoplight (on other cases)

Possible Causes

Depending on the make, year and model of the vehicle, Error Code P0175 may be triggered by a number of difference causes. Here are some of the most common possible causes:

  • Ignition misfires
  • Engine mechanical problems
  • Clogged, stuck or leaking fuel injector
  • Defective throttle position sensor
  • Defective or restricted fuel return line
  • Dirty or faulty MAP sensor
  • Dirty or faulty MAF sensor
  • Dirty or faulty O2 sensor
  • Faulty thermostat
  • Faulty fuel regulator
  • Faulty coolant temperature sensor
  • Problem on fuel delivery
  • Stuck open thermostat
  • Wrong fuel pressure
  • Vacuum leak
  • Outdated PCM software

How to Check

Diagnosis starts by checking the fuel pressure. You should inspect the fuel injectors for any restrictions.

Next, check the fuel injector pulse.

Then, check the fuel lines for signs of cracks or pinches.

Next, check all the vacuum lines for signs of deterioration, especially cracks.

Inspect the O2 sensors.

With the help of the scan tool, read the engine temperature and compare the findings with an infrared thermometer.

How to Fix

Fixes for this error code are pretty simple and straightforward, which you can achieve through a thorough diagnosis.

  • Check all vacuum hoses and PCV hoses. Replace if necessary.
  • Clean the MAF sensor. Make sure you consult with your manual for its specific location. The best way to clean it is to take it off and then spray it with a brake cleaner or electronics cleaner. Be cautious in cleaning the MAF sensor, and make sure it’s fully dry before reinstalling.
  • Inspect the fuel line for cracks, pinches and leaks.
  • Check the fuel rail’s fuel pressure.
  • Check the fuel injectors for dirt. Use the fuel injector cleaner. If you don’t know how to clean them, then it’s much better to have them professionally cleaned, if not replaced.
  • Check the exhaust leaks before the first O2 sensor. This may be unlikely to happen, but better not left any stones unturned.

For many Toyota and Lexus vehicles, contaminated MAF, common in aftermarket filters cause this code. Toyota hotwire MAFs are highly susceptible to contamination. Cleaning will not usually solve the problem. This is why the old MAF must be replaced including the engine air filter. Also, clean the air box and install new MAF and air filter, preferably using only OEM (original equipment manufacturer) parts to make sure the air box is properly sealed.