Check Engine Code P0171

Code P0171 "system too lean bank 1" means that the computer has noticed (by reading the oxygen sensors) that there is too much air going into bank one (the bank that includes cylinder number one in the firing order in v style engines).

This information is also applicable to code P0174, system too lean bank 2, as this code is the same except of the opposite bank of cylinders.

Engine control computers need to have a specific ratio of air to fuel in order to work properly, and if there is too much of one or the other then it will set a code.


What Causes a P0171 Code?

  • Dirty Mass Airflow Sensor
  • Vacuum Leak
  • Bad Oxygen Sensor(s)
  • Low Fuel Pressure
  • Running Out of Gas

Less Common Causes

  • Clogged Fuel Injectors
  • Leaking Exhaust System
  • Evaporative Emissions System Malfunction
  • EGR System Malfuncion

How to Fix Code P0171

1. Check Gas Level

The first thing that I would do is make sure no one has ran out of gas in the vehicle recently. This will cause the P0171 code to appear almost every time.

2. Clean MAF Sensor

If you decide to clean the MAF yourself you need to be very careful as it is very fragile. There is a small wire that you will be cleaning that is very easy to break. It is best to use just the aerosol mass airflow sensor cleaner as using a q-tip or something like that can leave debris on it and cause it to not read correctly.

Then you should check for vacuum leaks, especially ones that are after the MAF like tears in the tube that goes from the airbox to the engine. If this is torn it will let air in that the computer cannot tell is coming into the engine.

3. Check Oxygen Sensors

The next most common cause for this code code is bad oxygen sensors. If they are not working properly then they will not be reading the amount of oxygen in the exhaust gas.

4. Check Fuel Pressure

Another common cause of this code is low fuel pressure. If the fuel pump does not put the right pressure of fuel into the fuel system then the result can be this OBD code.

If you want to check it you will need to have a fuel pressure tester that will fit your fuel system. Then you just need to check the pressure. If it is low you need to replace the fuel filter first (unless it has been done recently). After the fuel filter has been changed you need to check the fuel pressure again. If it is still low, then you most likely have a fuel pump problem.

These are the easier things to check with code P0171. If none of this fixes it then it would be a good idea to take your car to a professional.

If you still have any unresolved vehicle problems or questions, you can ask an auto mechanic online. For expert answers specific to your vehicle's make and model, I recommend JustAnswer Car. They have a large pool of certified mechanics to answer your questions for a small fee and you can also browse their answers to other users for free.

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