P0170 Fuel Trim Malfunction Bank 1

P0170 indicates a fuel trim malfunction on bank 1. The controller cannot keep bank 1 fuel correction within expected limits.

Code details

Generic OBD-II · P0

System: Fuel / Air
Code type: Generic (SAE / ISO controlled)
Standard: SAE J2012 / ISO 15031-6

Diagnostic boundary

A diagnostic trouble code reports that a monitored test failed. It does not prove one specific part is bad, and manufacturer logic can add vehicle-specific conditions.

Do not replace oxygen sensors from fuel trim codes alone; verify air, fuel, exhaust, and sensor data first.

Symptoms of P0170

Check-engine light on, sometimes with rough or uneven running.
Hesitation, surging, or a noticeable change in fuel economy.
Occasionally hard starting or a smell of unburnt fuel.

Common causes of P0170

A failing or contaminated sensor (MAF, MAP, oxygen or air-fuel sensor).
Intake or vacuum leaks, or an exhaust leak near an upstream sensor.
Wiring, connector, or fuel-delivery problems that skew the reading.

Useful checks before replacing parts

Compare short-term and long-term fuel trims, oxygen sensor activity, MAF or MAP data, fuel pressure, and freeze-frame load.
Inspect intake leaks, exhaust leaks, fuel delivery, injector balance, vacuum hoses, PCV faults, and sensor contamination.
Check whether trim error is lean, rich, idle-only, load-only, bank-specific, or shared with related fuel trim codes.

Related OBD-II codes

These nearby fuel / air entries can help compare wording and pin down the fault area.