Failed downstream oxygen sensor (bank 2 sensor 3) due to contamination or age; Open or high-resistance wiring in the sensor signal circuit, including a bad connector or chafed harness; Poor ground connection at the sensor or engine block causing a voltage drop; Exhaust leak upstream of the sensor allowing outside air to skew the reading; Leaking fuel injector or rich condition on bank 2 that contaminates the sensor; Faulty engine coolant temperature sensor or thermostat stuck open causing a lean-running condition; Rarely, a failing engine control module driver for the oxygen sensor heater circuit

DTC codes / P01xx · Fuel and air metering / P0163

P0163O2 Sensor Circuit Low Voltage (Bank 2 Sensor 3)

Q: What does code P0163 mean?

O2 Sensor Circuit Low Voltage (Bank 2 Sensor 3). P0163 means the engine computer has detected a low-voltage condition on the downstream oxygen sensor circuit for bank 2 sensor 3, which is the post-catalytic converter sensor on the bank opposite cylinder one. The sensor's signal voltage stayed below the expected threshold for longer than the calibration allows, indicating either a lean exhaust stream, a wiring fault, or a failing sensor.

P0163 means the engine computer has detected a low-voltage condition on the downstream oxygen sensor circuit for bank 2 sensor 3, which is the post-catalytic converter sensor on the bank opposite cylinder one. The sensor's signal voltage stayed below the expected threshold for longer than the calibration allows, indicating either a lean exhaust stream, a wiring fault, or a failing sensor.

SystemPowertrain

Code typeGeneric (all makes)

SeverityLow

Fix difficultyIntermediate

AreaFuel and air metering

Symptoms you may notice

Illuminated check engine light, often with no other noticeable symptoms
A slight decrease in fuel economy as the computer adjusts fuel trim based on faulty feedback
Occasional rough idle or hesitation if the low voltage is caused by a lean condition
Failed emissions test due to the oxygen sensor monitor not completing or reporting a fault
In rare cases, a sulfur or rotten egg smell from the exhaust if the converter is being overworked

Common causes, most likely first

Failed downstream oxygen sensor (bank 2 sensor 3) due to contamination or age
Open or high-resistance wiring in the sensor signal circuit, including a bad connector or chafed harness
Poor ground connection at the sensor or engine block causing a voltage drop
Exhaust leak upstream of the sensor allowing outside air to skew the reading
Leaking fuel injector or rich condition on bank 2 that contaminates the sensor
Faulty engine coolant temperature sensor or thermostat stuck open causing a lean-running condition
Rarely, a failing engine control module driver for the oxygen sensor heater circuit

How to diagnose and fix it

Connect a scan tool and verify the code is current, then check live data for bank 2 sensor 3 voltage to confirm it is stuck low
Inspect the sensor wiring and connector for corrosion, chafing, or loose pins, and repair any damage found
Check for exhaust leaks between the converter and the sensor using a smoke machine or by listening for ticking
Measure the sensor heater resistance and compare to specification, and check the heater circuit for power and ground
Perform a propane enrichment test at the intake to see if the sensor voltage responds, which helps rule out a stuck sensor
Replace the downstream oxygen sensor only after electrical and exhaust integrity checks pass
Clear the code and complete a drive cycle to verify the repair and ensure the monitor runs without resetting

Downstream sensor codes are not always the sensor

A low voltage on a downstream sensor often indicates a lean exhaust stream rather than a dead sensor, so check fuel trims and look for vacuum leaks before condemning the part.
The bank 2 sensor 3 location is frequently exposed to road splash and debris, making harness chafing and connector corrosion more common than on upstream sensors.
An exhaust leak just ahead of the sensor can draw in outside air and produce a false low-voltage reading that mimics a failed sensor.
Replacing the sensor without addressing a rich-running condition or coolant temperature sensor fault will quickly foul the new part and set the code again.
Some vehicles use the downstream sensor to monitor catalyst efficiency, so a persistent low voltage may be an early warning of converter degradation rather than a sensor fault.

Can I keep driving with P0163?

The vehicle remains safe to drive with P0163 because the fault affects emissions monitoring rather than immediate engine operation. Avoid long-term driving with the light on, as continued operation with a faulty sensor can damage the catalytic converter and increase emissions.

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.