P0173
Fuel Trim Malfunction Bank 2
Fuel trims on bank 2 exceed adaptation limits in either lean or rich direction. The ECU cannot maintain stoichiometric mixture within calibrated boundaries.
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: medium
Common causes
Ordered by how often each turns out to be the cause.
- Oxygen sensor bank 2 agedCommon
- Vacuum leak bank 2 sidePossible
Parts involved
- Oxygen Sensor
- Mass Air Flow Sensor
- Fuel Injector
- Intake Manifold
P0173 is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.