Below is the basic causes and common fixes for a P0171 OBDII error code.
What Is a P0171 Error Code?
A P0171 code indicates there is a fuel/air mixture problem on bank 1 of the engine.
The term Lean means the cylinder is receiving too much or too little air creating a bad fuel mixture.
What Causes a P0171?
Several things can cause a P0171 with the most common failures being the Mass Air Flow Sensor or Vacuum Leak.
P0171 Error Code Fixes
There are several components that must work together to get the right air and fuel pressure mix.
A vehicle computer uses the mass air flow sensor to adjust the air mix into the engine.
For this reason the mass air flow sensor is commonly replaced to fix a a P0171 error code but may not be the problem.
A vacuum leak can cause the mass air flow sensor to get a bad reading.
The first step would be to clean the mass air flow sensor to see if the problem goes away or the vehicle runs better.
Next look for a vacuum leak using one of the many vacuum troubleshooting techniques.
Once a vacuum leak or mass air flow sensor is ruled out next step is to look at the fuel pressure.
A weak or failing fuel pump can case the pressure to be off messing up the mixture.
A clogged up fuel filter or pressure regulator can also cause this problem.
The fuel injector may also be failing causing a bad mixture to go into the cylinder.
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P0171 Fix Videos