P0170 Fuel trim malfunction (bank 1)
What P0170 means
Fuel trim is the correction the engine computer applies to keep the air-fuel mixture right. On bank 1 this correction has reached its limit, meaning the engine is running too lean or too rich and the computer can no longer compensate.
P0170 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
- 50–500 €
- 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 or unmetered air entering after the air flow meter
- Dirty or faulty mass air flow sensor
- Fuel pressure too low or too high (pump, filter or regulator)
- Leaking or clogged injectors
- Exhaust leak before the upstream oxygen sensor
Can I keep driving with P0170?
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
- Read the freeze-frame and live fuel trims: large positive values mean the engine runs lean, large negative values mean rich.
- If lean, check for vacuum leaks with a smoke test and inspect intake hoses and the PCV system.
- Clean or test the MAF sensor and check fuel pressure.
- If rich, check for leaking injectors, a stuck-open purge valve and high fuel pressure.
Related codes
- P0171 System too lean (bank 1)
- P0172 System too rich (bank 1)
- P0173 Fuel trim malfunction (bank 2)
- P0174 System too lean (bank 2)
- P0175 System too rich (bank 2)
- P0161 Oxygen sensor heater circuit (bank 2, sensor 2)
- P0160 Oxygen sensor circuit no activity detected (bank 2, sensor 2)
- P0181 Fuel temperature sensor A range/performance
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.
Updated: