P0173: Fuel trim malfunction (bank 2)
The ECU cannot keep the air and fuel mixture on bank 2 under control. Typical causes are an air leak, an injector or the oxygen sensor.
| Code | P0173 |
|---|---|
| System | Engine and transmission |
| Group | P01xx, Air and fuel metering |
| Type | Generic: it means the same on every make |
| Can you keep driving? | With care |
What P0173 means
Bank 2 is the side of the engine opposite cylinder 1, and it only exists on V or flat engines. The ECU corrects that side by adding or removing fuel, and this code means the correction has gone beyond what is acceptable. It can be too much or too little fuel, so the direction of the trim matters.
Most common causes
- Air leak in the intake manifold or a vacuum hose on bank 2
- Faulty bank 2 upstream oxygen sensor or damaged wiring to it
- Dirty, clogged or leaking injector on bank 2
- Exhaust leak ahead of the bank 2 oxygen sensor
- Dirty mass air flow (MAF) sensor, which affects both banks
Symptoms
- Engine warning light on
- Rough idle
- Loss of power or hesitation
- Fuel consumption different from usual
Can you drive with P0173?
With care You can drive, but a badly adjusted mixture wastes fuel, can cause misfires and may damage the catalytic converter. Have it checked before long.
How to check it
Compare the live long term fuel trim (LTFT) of both banks. If only bank 2 is off, the fault is on that side of the engine; if both are off, look at something shared such as the MAF sensor or fuel pressure.
How to read and clear P0173 with Final OBD
Plug an OBD2 scanner in under the steering wheel, switch the ignition on and open Final OBD. Under Faults you’ll see P0173 with this same explanation and whether it’s confirmed, pending or permanent.
With Free you read this code with its short description for nothing, and clear it if the engine stores it over standard OBD. With Pro you get the full explanation, how the car was running when it was logged (revs, temperature, load) and clearing in every control unit.
Clearing the code only turns the light off: if the cause is still there, it comes back. Clear it once it’s fixed, and not right before the ITV. It’s all in how to read and clear fault codes and in the ITV and OBD.
Similar codes
- P0161 Oxygen sensor heater (bank 2, sensor 2): circuit fault
- P0170 Fuel trim out of limits (bank 1)
- P0171 Mixture too lean (bank 1)
- P0172 System running too rich (bank 1)
- P0174 System running too lean (bank 2)
- P0175 System running too rich (bank 2)
- P0180 Fuel temperature sensor A circuit malfunction
- P0181 Fuel temperature sensor A range or performance problem
- P0100 Mass or volume air flow sensor circuit fault
- P0101 Air flow sensor range or performance problem
- P0102 Air flow sensor circuit low input
- P0103 Air flow sensor circuit high input
P0173 is a generic code, so it means the same on any make, for example on Audi, BMW, Fiat, Mazda, Peugeot, Volkswagen. See what Final OBD does on your car in makes and models.
What does code P0173 mean?
Bank 2 is the side of the engine opposite cylinder 1, and it only exists on V or flat engines. The ECU corrects that side by adding or removing fuel, and this code means the correction has gone beyond what is acceptable. It can be too much or too little fuel, so the direction of the trim matters.
Can you drive with P0173?
You can drive, but a badly adjusted mixture wastes fuel, can cause misfires and may damage the catalytic converter. Have it checked before long.
How do you clear P0173?
With an OBD2 scanner and an app like Final OBD, which clears it for free if it’s stored by the engine control unit. But clearing it only turns the light off: if the cause isn’t fixed, P0173 comes back.
Read it on your car
Final OBD reads the faults of every control unit for free, including each make’s own codes, and with Pro explains each one in plain English. Free clears engine faults at no cost.
Coming soon
Mid to late October 2026
If you want to try it in your car before anyone else, send us your email and we will add you as a tester.
info@finalobd.com