A failed oxygen sensor that is internally shorted or contaminated, causing a fixed rich bias; A wiring fault such as a short to voltage or chafed harness between the sensor and PCM; An exhaust leak upstream of the sensor that draws in air and skews the reading; A leaking fuel injector or high fuel pressure that genuinely makes the mixture rich; A restricted air intake or dirty mass airflow sensor causing inaccurate fueling; A PCM calibration issue or faulty PCM driver for that sensor circuit

DTC codes / P01xx · Fuel and air metering / P01F7

P01F7O2 Sensor Signal Biased/Stuck Rich Bank 1 Sensor 4

Q: What does code P01F7 mean?

O2 Sensor Signal Biased/Stuck Rich Bank 1 Sensor 4. P01F7 means the powertrain control module (PCM) has detected that the downstream oxygen sensor on bank 1, sensor 4, is reporting a mixture that stays biased rich or stuck rich beyond a calibrated threshold. The PCM monitors this sensor's voltage and compares it to expected behavior; when the signal remains higher than it should for too long, it flags the sensor as biased or stuck rich.

P01F7 means the powertrain control module (PCM) has detected that the downstream oxygen sensor on bank 1, sensor 4, is reporting a mixture that stays biased rich or stuck rich beyond a calibrated threshold. The PCM monitors this sensor's voltage and compares it to expected behavior; when the signal remains higher than it should for too long, it flags the sensor as biased or stuck rich.

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 PCM adds fuel based on the false rich signal
Possible rough idle or hesitation if the rich bias affects fuel trim enough
Black sooty exhaust or a strong fuel smell in severe cases
Failed emissions test due to the sensor monitor not completing or out-of-range readings

Common causes, most likely first

A failed oxygen sensor that is internally shorted or contaminated, causing a fixed rich bias
A wiring fault such as a short to voltage or chafed harness between the sensor and PCM
An exhaust leak upstream of the sensor that draws in air and skews the reading
A leaking fuel injector or high fuel pressure that genuinely makes the mixture rich
A restricted air intake or dirty mass airflow sensor causing inaccurate fueling
A PCM calibration issue or faulty PCM driver for that sensor circuit

How to diagnose and fix it

Connect a scan tool and record freeze-frame data and fuel trim values to confirm the rich bias
Visually inspect the sensor, its connector, and the wiring harness for damage or contamination
Check for exhaust leaks between the engine and the sensor using a smoke test or listening for ticks
Measure the sensor's signal voltage with a multimeter and compare to the scan tool reading to verify circuit integrity
Test for a short to voltage on the signal wire with the sensor disconnected and the key on
Replace the oxygen sensor if it is confirmed stuck rich and the wiring tests good
Clear the codes and perform a road test to verify the repair and that the monitor completes

Why a rich code may not be the sensor

A stuck-rich downstream sensor often follows a genuine rich condition upstream, so check fuel trims and injector balance before condemning the sensor.
Exhaust leaks before the sensor can pull in outside air and cause a lean reading, but a leak after the sensor can trap rich exhaust and falsely bias the sensor rich.
Contamination from silicone sealants or coolant can coat the sensor element and cause a permanent rich bias that no amount of cleaning will fix.
Some vehicles use a wideband sensor for sensor 4, and a biased reading may indicate a reference circuit fault rather than a failed sensing element.
A faulty thermostat that keeps the engine cold can cause the PCM to command a rich mixture, indirectly setting this code without any sensor fault.

Can I keep driving with P01F7?

You can usually drive the vehicle short distances to a repair shop, but avoid heavy acceleration or towing because the rich condition can damage the catalytic converter over time. If the check engine light is flashing or you notice rough running, stop driving and seek immediate service.

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.