P0170: Fuel Trim Bank 1

What does P0170 mean?

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.

The code tells you which monitor failed, not which part is broken. Test before replacing parts.

Symptoms

• Check engine light on (after two drive cycles)
• Rough idle or hesitation
• Higher consumption
• Often no symptoms

Common causes

• High Air flow sensor dirty or drifting
• Medium Air leak or crankcase ventilation leaking
• Medium Injection quantity error (diesel: injector drift, rail pressure sensor; petrol: injectors, fuel pressure)
• Low Oxygen or NOx sensor offset

Likelihood is a general estimate across vehicles; your make and model may differ.