P0170 — Fuel Trim Malfunction (Bank 1)

The controller detected a fuel-trim malfunction on bank 1. This code alone does not specify whether the mixture is too lean or too rich. Bank 1 contains cylinder 1; determine its physical location from the engine information.

Affected system: Powertrain

Symptoms

• Engine warning light, uneven idle or hesitation.
• Changed fuel consumption and possible loss of power, depending on the correction problem.

Possible causes

• Unmetered air or inaccurate MAF/MAP information.
• Incorrect fuel delivery, injector problems or inaccurate oxygen-sensor information.

What to check

• Identify bank 1 and save operating conditions; review related airflow, temperature, misfire and oxygen-sensor codes.
• With the engine warm in closed loop, log STFT and LTFT at idle and light load.
• Establish correction direction before testing: positive values add fuel and negative values remove it, using the scan tool’s convention.
• Follow the results with intake/exhaust leak and fuel-pressure checks, then evaluate oxygen-sensor response; do not replace it from this code alone.
• After repair, clear codes and recheck bank 1 fuel trims under the original recorded conditions, following the manufacturer’s procedure.

Also written as: P0170-00, P017000, PO170 (some scan tools add the fault-type byte, e.g. -00).