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.
Medium severity. Can I keep driving?You can drive in moderation for a short time. A very lean or very rich mixture can damage the engine or the catalytic converter.
Bank 1 is the side of the engine with cylinder 1. Inline engines only have this bank.
Symptoms
- Check engine light on (after two drive cycles)
- Rough idle or hesitation
- Higher consumption
- Often no symptoms
Most likely causes
- Air flow sensor dirty or drifting
- Air leak or crankcase ventilation leaking
- Injection quantity error (diesel: injector drift, rail pressure sensor; petrol: injectors, fuel pressure)
- Oxygen or NOx sensor offset
What to check, in order
Start with the simplest. You can tick off each step.
Good to know
- Repair difficulty: medium
- It affects emissions.
What each character of P0170 means
- P: Powertrain: engine and transmission
- 0: Generic code: same on every make
- 1: Air and fuel
- 70: Specific fault in that system
Frequently asked questions
Can I keep driving with code P0170?
You can drive in moderation for a short time. A very lean or very rich mixture can damage the engine or the catalytic converter.
What causes code P0170?
The most common causes are: air flow sensor dirty or drifting; air leak or crankcase ventilation leaking; injection quantity error (diesel: injector drift, rail pressure sensor; petrol: injectors, fuel pressure).
Related codes
- P0173Fuel Trim Bank 2
- P0171System Too Lean Bank 1
- P0172System Too Rich Bank 1
- P0101Mass or Volume Air Flow Sensor A Circuit Range/Performance
- P0263Cylinder 1 Contribution/Balance
Sources
- law.cornell.edu: 13 CCR 1968.2
- fordservicecontent.com: obd summary diesel 2023
- automotivetechinfo.com: Causes of DTCs P0170 and P0173 in Mercedes Benz Ve
Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.