P0163
O2 Sensor Circuit Low Voltage (Bank 2, Sensor 3)
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P0163 is triggered when the PCM detects a persistently low voltage from the third oxygen sensor on Bank 2. This sensor is found on vehicles with dual-stage catalytic converter setups and sits behind the secondary catalytic converter. A low voltage reading indicates the sensor is seeing a lean exhaust condition — either because the exhaust is genuinely lean at that point, or because the sensor has failed.
This is one of the less impactful O2 sensor codes because Sensor 3 is the furthest downstream monitor in the exhaust system. It has minimal influence on fuel trim calculations and primarily exists for emissions compliance monitoring of the secondary catalytic converter. Most drivers will not notice any change in how the vehicle drives.
The standard repair is replacing the oxygen sensor, though you should first check for exhaust leaks near the sensor and inspect the wiring harness. Sensor 3 may be more difficult to access than upstream sensors, potentially requiring the vehicle to be raised on a lift. Parts cost is similar to other O2 sensors, but labor may be slightly higher due to the location.
Severity
Symptoms
- •Check Engine Light is on
- •Marginally decreased fuel economy
- •Slight increase in exhaust emissions
- •No significant performance changes
- •Failed emissions inspection
- •Possible faint exhaust smell
Likely Causes
The third oxygen sensor on Bank 2 has aged or failed, causing it to produce a constant low voltage signal indicating a lean exhaust reading.
A broken wire or high-resistance connection in the sensor signal circuit is dropping the voltage reading below normal operating range.
An exhaust leak near the sensor allows ambient air to dilute the exhaust stream, causing the sensor to read lean and produce a low voltage signal.
An actual lean fuel condition on Bank 2 is causing legitimately low exhaust oxygen levels at the third sensor location.
Corrosion at the sensor connector creates resistance that reduces the voltage signal reaching the PCM.
Estimated Cost
Professional Repair
Includes parts + labor
Common Fixes
- Replace the Bank 2 Sensor 3 oxygen sensor
- Repair damaged or broken wiring in the sensor circuit
- Seal exhaust leaks near the sensor mounting point
- Clean or replace corroded connectors