O2 Sensor Circuit Low Voltage (Bank 2, Sensor 3)
The P0163 code means the vehicle's onboard diagnostic system has detected: O2 Sensor Circuit Low Voltage (Bank 2, Sensor 3). This is a moderate severity code.
- Keep driving?
- Short distances only
- DIY difficulty
- moderate
- Estimated cost
- $100 - $350 (parts and labor)
Test O2 sensor voltage (should fluctuate 0.1-0.9V). Do not replace a $150 sensor without confirming it is actually bad first.
Shows real-time O2 sensor readings on your phone. See if the sensor is lazy, stuck, or actually working before spending money.
Affiliate links — we earn a commission at no extra cost to you.
Common Symptoms
- Check Engine Light illuminated
- Poor fuel economy
- Possible lean running condition
- Emissions test failure
Probable Causes (Ranked by Likelihood)
- Failed O2 sensor reading lean (Bank 2, Sensor 3) Very High
- Exhaust leak before sensor allowing fresh air in High
- Damaged sensor wiring (shorted to ground) Moderate
- PCM reference voltage issue Low
Common Fixes by Vehicle
What techs usually find when diagnosing P0163 on specific vehicles — tap your vehicle for the fix and the exact part:
2004-2010 Ford F-150 5.4L 3V Triton V8 easy DIY
Replace Bank 2 Sensor 3 (tailpipe-end) O2 sensor with an OE-quality Motorcraft unit. Ford trucks with dual exhaust have three sensors per bank -- S3 is the rearmost. Verify wiring hasn't been melted by the heat shield bolt area (common chafe point).
Labor: 30 min2003-2014 Ford Expedition/Navigator 5.4L easy DIY
Replace the rearmost B2 O2 sensor. Before replacing, check for exhaust leaks at the Y-pipe to the rear cat -- Expedition cats crack at the inlet flange. If leak is present, a fresh sensor will throw the same code.
Labor: 45 min2000-2005 Ford Excursion 6.8L V10 moderate DIY
V10 has three sensors per bank -- B2S3 is deepest on passenger side. Use 7/8 offset O2 socket with extensions. NTK Ford OEM sensor required. If code returns, check for failing coils on bank 2 causing rich burn.
Labor: 1 hourFrequently Asked Questions
What does low voltage mean on an O2 sensor?
Low voltage (below 0.2V) means the sensor is reporting a lean condition, from a failed sensor, exhaust leak, or wiring short to ground.
Can an exhaust leak cause P0163?
Yes, an exhaust leak before the sensor allows fresh air into the exhaust stream, making the sensor read lean and producing a low voltage signal.
Should I replace the O2 sensor or check wiring first?
Always check wiring and exhaust leaks first. A visual inspection and simple voltage test can save you the cost of an unnecessary sensor replacement.
What actually makes the computer set an oxygen sensor code?
The OBD II regulation requires four separate detections for an oxygen sensor (Title 13 CCR 1968.2, section (e)(7.2)): deterioration in voltage, response rate or amplitude that would push emissions past 1.5 times the FTP standards; loss of circuit continuity; out-of-range values; and the case where the sensor has degraded enough that the fuel system stops using it and falls back to open loop. A sensor can therefore set a code while still producing a signal that looks plausible on a scan tool. This is the threshold the monitor is designed around, not a description of your specific fault — the regulation says what the system must detect, not how to find it on your vehicle.
Mechanics Guide Step-by-step diagnosis
Step-by-Step Diagnostic Procedure
-
Read Bank 2 Sensor 3 voltage. Constant reading below 0.2V indicates a stuck lean sensor.
-
Inspect for exhaust leaks in the pipe section between the catalytic converter and the sensor.
-
Check sensor wiring for shorts to ground or damaged insulation.
-
Measure sensor signal wire voltage with sensor disconnected. Should see PCM bias voltage (around 0.45V).
Sources 3
This page is built from documented references. Verify against your own service info before repair work.
- California Code of Regulations, Title 13 section 1968.2 (OBD II)malfunction criteria, section (e)
- SAE J2012Diagnostic Trouble Code Definitions (defines the generic OBD-II code ranges)
- Cross-checked against the SAE J2012:2002 DTC table (2026-08-27)archived scan of the SAE standard — readable copy, not SAE’s current edition
Commonly Affected Vehicles
- 2010-2020 Ford F-250 (6.2L V8)
- 2012-2019 Chevrolet Tahoe (5.3L V8)
- 2008-2018 Toyota Sequoia (5.7L V8)
- 2011-2020 GMC Sierra (5.3L V8)
Related Codes
See All Codes & Fixes for Your Vehicle
Explore More
Was this helpful?
Send this to whoever is fixing the car — your mechanic, or the person asking what the light means.