How do I fix a P0172 error code?

Alton Alexander
By Alton AlexanderUpdated on June 4th, 2022

P0172 is a code for too rich a mixture in Bank 1. This can be caused by a faulty oxygen sensor, mass air flow sensor, or fuel injector. It can also be caused by a vacuum leak or a problem with the fuel pressure regulator.

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1. Check for vacuum leaks and repair as necessary

  1. Remove the screws that fasten the fuel rail to the engine block.
  2. Lift the fuel rail off of the engine block.
  3. Check for any cracks or tears in the fuel rail. If there are any, replace the fuel rail.
  4. Check for any vacuum leaks around the fuel rail. If there are any, repair the leaks.
  5. Replace the fuel filter if necessary.
  6. Reinstall the fuel rail and screws.

2. Check the engine's air filter and replace it if it is dirty

  1. Remove the air filter cover.
  2. Locate the air filter. It is usually located on the left or right side of the engine.
  3. Remove the air filter.
  4. Clean the air filter.
  5. Replace the air filter.

3. Inspect the engine's oxygen sensors and replace them if they are faulty

  1. Start the vehicle and allow it to idle for a few minutes to warm up the engine.
  2. Locate the oxygen sensor bungs on either side of the engine.
  3. Disconnect the oxygen sensor connectors.
  4. Inspect the oxygen sensor for damage. If the sensor is damaged, replace it.
  5. Reconnect the oxygen sensor connectors.
  6. Start the vehicle and drive it for a few minutes to check for any irregularities. If there are no problems, replace the oxygen sensor.

4. Check the fuel injectors and clean or replace them if they are dirty

  1. Disconnect the negative battery cable.
  2. Remove the fuel rail cover.
  3. Remove the fuel injectors.
  4. Clean the injectors if necessary.
  5. Reinstall the fuel injectors.
  6. Connect the negative battery cable.
  7. Reconnect the air intake hose.
  8. Reconnect the exhaust hose.
  9. Start the engine and check the engine performance.

Some users might also have success with the following opitons:

  1. Adjust the air/fuel mixture by turning the mixture screws on the carburetor.
  2. Have the engine's computer system checked for faults.