A failed or contaminated bank 1 sensor 4 oxygen sensor that reads lean regardless of actual exhaust oxygen; An exhaust leak upstream of the sensor, such as a cracked pipe or failed gasket, allowing outside air to reach the sensor; A wiring fault in the sensor circuit, including chafed wires, corroded connectors, or a poor ground; A stuck-open or leaking fuel injector on bank 1 causing a genuine lean condition that the sensor correctly reports; A vacuum leak on bank 1 that leans the mixture and drives the downstream sensor signal low; A failing catalytic converter that no longer stores oxygen properly, altering the downstream sensor's expected switching; Low fuel pressure or a weak fuel pump that starves the engine and produces a lean exhaust stream

DTC codes / P01xx · Fuel and air metering / P01F6

P01F6O2 Sensor Signal Biased/Stuck Lean Bank 1 Sensor 4

Q: What does code P01F6 mean?

O2 Sensor Signal Biased/Stuck Lean Bank 1 Sensor 4. P01F6 indicates that the powertrain control module has detected a lean bias or stuck-lean condition on the downstream oxygen sensor for bank 1 sensor 4, meaning the sensor's voltage stays lower than expected for the exhaust oxygen content. The computer compares this signal against other sensors and its fueling model, and it flags the code when the reading remains lean beyond a calibrated time and threshold.

P01F6 indicates that the powertrain control module has detected a lean bias or stuck-lean condition on the downstream oxygen sensor for bank 1 sensor 4, meaning the sensor's voltage stays lower than expected for the exhaust oxygen content. The computer compares this signal against other sensors and its fueling model, and it flags the code when the reading remains lean beyond a calibrated time and threshold.

SystemPowertrain

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaFuel and air metering

Symptoms you may notice

Illumination of the check engine light, often with no other noticeable symptoms
A slight decrease in fuel economy as the engine runs richer to compensate
Occasional rough idle or hesitation during light acceleration
A faint sulfur or rotten-egg smell from the exhaust in some cases
Failed emissions inspection due to the stored code and monitor status
In rare cases, a lean misfire or surging at steady cruise speeds

Common causes, most likely first

A failed or contaminated bank 1 sensor 4 oxygen sensor that reads lean regardless of actual exhaust oxygen
An exhaust leak upstream of the sensor, such as a cracked pipe or failed gasket, allowing outside air to reach the sensor
A wiring fault in the sensor circuit, including chafed wires, corroded connectors, or a poor ground
A stuck-open or leaking fuel injector on bank 1 causing a genuine lean condition that the sensor correctly reports
A vacuum leak on bank 1 that leans the mixture and drives the downstream sensor signal low
A failing catalytic converter that no longer stores oxygen properly, altering the downstream sensor's expected switching
Low fuel pressure or a weak fuel pump that starves the engine and produces a lean exhaust stream

How to diagnose and fix it

Inspect the bank 1 sensor 4 wiring and connector for damage, corrosion, or loose pins, and repair as needed
Perform a visual and smoke test of the exhaust system upstream of the sensor to find leaks
Use a scan tool to view live oxygen sensor voltage and compare bank 1 sensor 4 against bank 1 sensor 2 and fuel trim data
Check fuel pressure and inspect for vacuum leaks on bank 1 using a smoke machine or propane enrichment
Test the oxygen sensor's heater circuit and signal response with a multimeter or oscilloscope before condemning the sensor
Replace the bank 1 sensor 4 oxygen sensor only after confirming the circuit and exhaust are sound
Clear the code and complete a drive cycle to verify the repair and confirm the monitor runs to completion

Why a lean code is not always the sensor

A downstream oxygen sensor that reads lean is often reporting a real lean condition caused by an exhaust leak or vacuum leak, so replacing the sensor first frequently fails to fix the code.
Bank 1 sensor 4 is typically a downstream sensor on a V8 or V6 engine, and its signal is heavily influenced by catalytic converter efficiency, so a tired converter can set this code without any sensor fault.
Corroded or oil-contaminated sensor connectors are a common hidden cause, especially on vehicles that have had recent engine work or a valve cover gasket leak.
Fuel trim data is the fastest way to separate a true lean condition from a biased sensor: positive long-term fuel trims on bank 1 point to a real lean mixture, while normal trims with a low sensor voltage point to the sensor or its circuit.
A stuck-lean sensor can be intermittent, so a wiggle test of the harness while watching live data often reveals a wiring problem that a static resistance check misses.

Can I keep driving with P01F6?

You can usually drive the vehicle short distances to a repair shop, but avoid sustained high-speed or heavy-load driving because a genuine lean condition can overheat the catalytic converter and cause costly damage. If the check engine light begins flashing or the engine runs rough, stop driving and have it towed.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.