P0170 — Fuel Trim — Bank 1
P0170 is the standardized powertrain DTC for “Fuel Trim — Bank 1.” The code identifies the monitored condition; it does not by itself prove which part failed.
What P0170 means
P0170 is the standardized powertrain DTC for “Fuel Trim — Bank 1.” The code identifies the monitored condition; it does not by itself prove which part failed.
Bank/sensor location note
Bank 1 is the cylinder bank containing cylinder No. 1. On an inline engine there is normally only one bank. Do not guess bank location from left/right orientation; verify the engine-specific service information.
Possible symptoms
- Check Engine Light
- Possible rough idle, hesitation, or poor fuel economy
- Fuel trims at or near adaptive limits
- Possible lean/rich companion codes
Causes to test
These are diagnostic possibilities, not a statistical parts-replacement ranking. Vehicle-specific service information takes priority.
- Unmetered air or intake/PCV/purge leak
- Fuel-pressure or injector delivery problem
- MAF/MAP/load measurement error
- Exhaust leak or biased upstream O2/A/F feedback
- Engine mechanical condition affecting airflow or combustion
Step-by-step diagnostic workflow
- Record STFT/LTFT by bank at idle and at a steady higher RPM.
- Compare both banks to distinguish shared causes from bank-specific faults.
- Check intake leaks, purge flow, fuel pressure, and airflow/load data.
- Inspect upstream exhaust leaks and O2/A/F sensor response.
- Resolve misfire and mechanical faults before condemning mixture sensors.
- Clear codes only after repair, then complete an appropriate drive cycle and verify the code and symptoms do not return.
Scan data worth checking
- STFT/LTFT by bank
- MAF/MAP and calculated load
- Upstream O2/A/F feedback
- Fuel pressure/rail pressure
- Purge command and misfire data
Severity and drivability
Moderate. Fuel-trim faults mean the control module cannot keep mixture correction within its expected adaptive range; drivability and catalyst impact depend on the underlying cause.
Stop driving and investigate immediately if there is a flashing MIL, oil-pressure warning, overheating, fuel leakage, severe misfire, major loss of power, abnormal mechanical noise, or a transmission that is slipping badly.
Common diagnostic mistakes
- Treating a fuel-trim code as proof an oxygen sensor failed
- Reading fuel trims at only one operating condition
- Ignoring a common cause when both banks move in the same direction
Related generic codes
Source and accuracy notes
Generic DTC structure and standardized definitions are governed by SAE J2012/J2012DA. Actual enable criteria, thresholds, circuit pinouts, test values, software conditions, and repair procedures vary by vehicle. Use current OEM service information for the exact year/engine/calibration and check applicable manufacturer technical service bulletins. See the site methodology and primary-reference policy.