P0173 Fuel trim malfunction (bank 2)
What P0173 means
The engine computer's mixture correction on bank 2 has reached its limit, meaning that side of the engine is running too lean or too rich and the computer can no longer compensate. Bank 2 is the side of a V6, V8 or boxer engine that does not contain cylinder 1.
P0173 is a generic SAE J2012 code: it means the same on every make. The exact cause still depends on the car, so read the freeze-frame data before replacing parts.
At a glance
- Severity
- Medium
- Typical repair cost
- 100–600 €
- Workshop time
- 0.5–3 h
- Repair difficulty
- Medium
- DIY possible
- Yes
- Check engine light
- Yes
- Affects emissions test
- Yes
Parts and labour at an independent workshop in Europe. Main dealers charge more; the cause decides the bill, not the code.
Symptoms
- Check engine light on
- Higher fuel consumption
- Rough idle or hesitation
- Possible loss of power
Common causes
- Vacuum leak on the bank 2 side, such as an intake gasket
- Dirty or faulty mass air flow sensor
- Fuel pressure too low or too high
- Leaking or clogged injectors on bank 2
- Exhaust leak before the bank 2 upstream oxygen sensor
Can I keep driving with P0173?
You can drive, but have it checked within one to two weeks. A mixture that stays wrong increases fuel use and can harm the catalytic converter.
What to check first
- Compare fuel trims on both banks: if both are off, look for a shared cause (MAF, fuel pressure, large vacuum leak); if only bank 2, look at that side.
- Smoke-test the intake for leaks, paying attention to the bank 2 intake gasket.
- Check fuel pressure and the MAF sensor.
- Check bank 2 injectors and the exhaust manifold for leaks.
Related codes
- P0172 System too rich (bank 1)
- P0174 System too lean (bank 2)
- P0171 System too lean (bank 1)
- P0175 System too rich (bank 2)
- P0170 Fuel trim malfunction (bank 1)
- P0181 Fuel temperature sensor A range/performance
- P0161 Oxygen sensor heater circuit (bank 2, sensor 2)
- P0160 Oxygen sensor circuit no activity detected (bank 2, sensor 2)
Data: TORKO fault-code catalogue, built on OBDex (CC0-1.0) and reviewed against workshop practice. Informational only — it does not replace a diagnosis by a mechanic.
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