System Too Rich Bank 1
Your engine computer has detected too much fuel and not enough air in the air-fuel mixture on bank 1. This can cause rough running, poor fuel economy, black smoke, and damage to the catalytic converter if ignored.
You can usually drive short distances if the vehicle runs normally, but avoid heavy driving and fix it soon. If the engine runs rough, misfires, smells strongly of fuel, or the check engine light is flashing, stop driving and repair it immediately.
P0172 means the powertrain control module has reached the limit of fuel correction while trying to reduce a rich condition on bank 1. The oxygen or air-fuel ratio sensor feedback shows the exhaust is consistently rich, so the PCM stores this code when fuel trims stay too negative for too long.
Bank 1 is the side of the engine that contains cylinder number 1. On inline engines, there is only one bank, so bank 1 refers to the whole engine.
Yes. A dirty or faulty mass airflow sensor can report incorrect airflow and cause the PCM to command too much fuel.
Yes. A rich mixture uses more fuel than normal, so reduced fuel economy is very common with this code.
They can contribute if misfires leave unburned fuel in the exhaust, but spark plugs are not the most common direct cause of P0172.
Yes. If left unfixed, it can foul spark plugs, damage the catalytic converter, and cause poor running.