Toyota Sequoia P0172: Fuel System Rich – Bank 1

A common trouble code with the Toyota Sequoia is P0172. This code number references a number that is given to you when you plug your car into a OBDII scanner. It’s not the most complicated OBDII trouble code to diagnose. It is also one of the most common. It means that the motor is running with a rich condition.

Toyota Sequoia P0172 Fuel System Rich Diagnosis


Sequoia P0172 Code Defined

P0172 is thrown when the oxygen sensors detect that the air fuel mixture is too rich. Bank 1 refers to the rich condition being detected on the side of the engine with cylinder 1.

A rich condition indicates that the air fuel mixture has too much fuel or not enough air. This would be the opposite of a lean condition, which’ll throw P0171.

Sequoia P0172 Code Symptoms

P0172 Toyota Sequoia

The P0172 code on a Toyota Sequoia will often be thrown if the fuel injection system is not operating properly. Typically the code will be triggered by a rich condition in the engine.

There aren’t usually any drivability issues associated with P0172. For most people the first sign that anything is wrong at all is the service engine soon light coming on.

Here are the typical symptoms that something is wrong when you have code P0172.

  • Mileage- may or may not suffer depending on how much the air fuel mixture has changed.
  • Misfire– If the air fuel mixture has gotten too far from factory specs, this can cause the Sequoia to misfire.
  • Idle Issues– With the air/fuel mixture altered, the vehicle can idle erratically as the computer compensates to keep the engine running.
  • Exhaust Smell/Color– Depending on how rich the motor is running, there could be some exhaust odor or discoloration.
  • Fouled Spark Plugs– The spark plugs can foul if the engine runs very rich for a long enough period of time.


This youtube video is a great resource for diagnosing the P0172 trouble code in your Sequoia.

Top Toyota Sequoia P0172 Causes

Here are the most common causes of P0172:

  • Vacuum Leaks– With the Toyota Sequoia, one of the most common cause for the P0172 code to show is a vacuum leak. Take a look around and see if you can find the vacuum leak. Here’s a great YouTube video on how to find a vacuum leak.
  • Oxygen Sensor– The P0172 codes is thrown when the oxygen sensor(s) do not register the right amount of oxygen in the exhaust. When the oxygen sensor is bad, it can cause a false reading and trigger the code. The computer will still adjust the air/fuel mixture to compensate. This will cause the Sequoia to run rich. Toyota Sequoia O2 Sensor
  • Mass Air Flow Sensor– The mass air flow sensor calculates the volume of air entering the engine. If it has gone bad, the air fuel mixture will be off and the P0172 code will show.
  • Bad Fuel Injectors– If you have one or more fuel injectors that have gone bad that can certainly cause the air/fuel mixture to go bad.
  • Fuel Pump/Fuel Filter– Today’s modern fuel injected motors need a lot of fuel pressure to atomize the gas properly. If the fuel pressure is off, atomization doesn’t happen properly and the optimal air/fuel mixture isn’t achieved.
  • Air Filter– While it’s not the most common reason to throw the P0172 code, a clogged air filter certainly can cause the code to throw. And, since it’s so easy to check, why not look?

Good luck figuring out what is wrong with your Sequoia. If there is anything that you feel could improve the article, please feel free to comment or message. Thank you.