P0170Fuel Trim Bank 1
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- With closed-loop control the engine module corrects the injected fuel using the oxygen sensor: short-term fuel trim reacts within fractions of a second, long-term trim stores a learned base correction per load and speed range. Positive values mean fuel is being added because the mixture was lean, negative values mean fuel is being removed; around ±10 % is normal. P0170 is the older, direction-neutral code for 'mixture adaptation of bank 1 out of range'; whether lean or rich has to be read from the trim values. Users are Mercedes-Benz petrol engines, which often set P0170/P0173 instead of P0171–P0175 – a Mercedes-Benz magazine for independent workshops reports that cleaning or replacing the air flow sensor most often cures it – and Ford's 6.7 litre diesel, where it flags a fuel quantity error above 15 % in either direction from its fuel mass observer. GM and Ford petrol engines do not use it. Two trips.
- What you may notice
- Check engine light on (after two drive cycles)
- Rough idle or hesitation
- Higher consumption
- Often no symptoms
- Likely causes
- LikelyAir flow sensor dirty or drifting
- PossibleAir leak or crankcase ventilation leaking
- PossibleInjection quantity error (diesel: injector drift, rail pressure sensor; petrol: injectors, fuel pressure)
- RareOxygen or NOx sensor offset
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Often possible to do yourself.Typical cost: €20 – €600
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.