What does the P0163 code mean?
The P0163 is a generic OBD-II powertrain trouble code. Its official definition is “O2 Sensor Circuit Low Voltage (Bank 2, Sensor 3)“.
When you connect a vehicle code reader to the diagnostic link connector, the powertrain control module (PCM) reports P0163 if it detects that the voltage signal from the third oxygen sensor on Bank 2 (Sensor 3, located after the second catalytic converter or downstream of a diesel particulate filter) is staying below a minimum threshold for an extended period. A healthy oxygen sensor typically oscillates between 0.1 V (lean) and 0.9 V (rich). If the voltage remains persistently low (usually below 0.1–0.2 V) or near 0 V, the PCM interprets this as a low voltage condition and sets P0163. Bank 2 is the engine bank that does not contain cylinder #1. Sensor 3 is not present on all vehicles; it is typically found on hybrids, SULEV/PZEV vehicles, or diesel aftertreatment systems. Using a professional car scanner with live data graphing allows technicians to see the flatlined low voltage waveform. An obd2 scanner can also display the exact voltage reading and compare it to other sensors. Unlike codes like P0162 (general circuit malfunction) or P0164 (high voltage), P0163 specifically indicates the signal is stuck low.
Symptoms of Error Code P0163
- Malfunction Indicator Lamp (MIL) illuminated
- Usually no noticeable drivability issues – the sensor mainly monitors catalyst efficiency
- Failed emissions test due to the PCM being unable to properly evaluate the catalytic converter or DPF
- Possible related codes such as P0420, P0430, or P0162 may also appear
- On diesel vehicles, possible regeneration issues if the sensor monitors DPF efficiency
- In rare cases, slightly reduced fuel economy if the PCM uses default values
Main Causes of Error Code P0163
- Faulty oxygen sensor (Bank 2 Sensor 3) – internal short to ground or failed sensing element
- Shorted signal wire to ground in the sensor harness
- Corroded or damaged connector causing poor signal transmission
- Exhaust leak upstream of the sensor allowing fresh air to dilute the sample, causing a false lean reading
- Contaminated sensor tip (oil, coolant, fuel additives) causing incorrect low voltage output
- PCM internal fault (rare)
How to Diagnose Error Code P0163?
- Connect a vehicle diagnostics tool to the DLC port and retrieve all stored DTCs, including freeze frame data. Note engine temperature, RPM, and fuel trim values.
- Perform a visual inspection of the Bank 2 Sensor 3 oxygen sensor, its wiring, and connector. Look for physical damage, corrosion, broken wires, or melted insulation.
- Start the engine and bring it to normal operating temperature (approximately 190–220 °F). Use a car code scanner with live data graphing to monitor the B2S3 voltage. If the voltage stays below 0.1 V and never rises, there is a low voltage condition.
- Disconnect the sensor and measure the voltage at the PCM side of the connector. If the voltage jumps to around 0.45 V (reference voltage), the sensor is likely shorted internally. If it remains low, there may be a wiring short to ground.
- Check for exhaust leaks near the sensor using a smoke machine or by listening for hissing sounds. Fresh air entering the exhaust can cause a falsely lean (low voltage) reading.
- Measure the resistance of the sensor’s internal elements (heater and signal circuit) using a DVOM. Compare with manufacturer specifications.
- If the sensor and wiring appear intact, perform a propane enrichment test. Introduce propane into the intake and watch if the B2S3 voltage rises. If it stays low, the sensor is faulty.
- Clear the code with an obd2 scanner after repairs and perform a complete drive cycle to verify the fix.
Possible Causes and Diagnostic Methods
| Possible Cause | How to Check? |
| Faulty B2S3 oxygen sensor (internal short) | Disconnect sensor; monitor voltage at PCM connector – if voltage jumps to 0.45 V, sensor is shorted |
| Signal wire shorted to ground | Check continuity between signal wire and ground with DVOM; should be infinite resistance |
| Corroded connector | Visual inspection; clean with contact cleaner; check pin tension |
| Exhaust leak upstream of sensor | Smoke test exhaust system; listen for hissing; look for soot marks |
| Contaminated sensor tip | Remove sensor and inspect tip for deposits; replace if contaminated |
| PCM failure | Only after ruling out all other possibilities; check for TSBs |
Tools needed: obd2 scanner or vehicle diagnostics tool, digital volt/ohmmeter (DVOM), exhaust smoke machine, propane enrichment kit, wiring diagram, basic hand tools, safety glasses.
How do I fix error code P0163? (Solutions to the Problem)
Simple Fixes
- Clear the code with a vehicle code reader and drive for a few days. If the code does not return, it may have been a temporary glitch.
- Clean the sensor connector contacts with electrical contact cleaner and re-seat firmly.
- Tighten any loose exhaust clamps or bolts near the sensor that could cause a minor leak.
In-depth Diagnosis and Repair Solutions
- Replace the Bank 2 Sensor 3 oxygen sensor with an OEM or high-quality aftermarket unit. This resolves the majority of P0163 cases caused by internal sensor failure.
- Repair or replace damaged wiring that is shorted to ground. Solder and heat-shrink any repairs.
- Weld or patch exhaust leaks found upstream of the sensor. Replace gaskets at flanges.
- If the sensor tip is contaminated, identify and fix the source of contamination (oil leak, coolant leak, rich condition) before replacing the sensor.
- Apply a manufacturer PCM update if a TSB addresses low voltage detection thresholds on your specific model.
Fix faults based on symptoms
| Observed Symptom | Likely Root Cause | Recommended Action |
| B2S3 voltage stuck near 0 V; rises when sensor disconnected | Internal short in sensor | Replace B2S3 sensor |
| B2S3 voltage stuck near 0 V; remains low when sensor disconnected | Signal wire shorted to ground | Repair wiring harness |
| B2S3 voltage low but fluctuates slightly | Exhaust leak or contamination | Repair exhaust leak; clean or replace sensor |
| Code returns after sensor replacement | Persistent exhaust leak or PCM issue | Re-check for leaks; check for TSB; consider reflash |
Common Error Code P0163 in Vehicles
Toyota & Lexus: On certain Toyota Camry Hybrid and Lexus RX 400h models with SULEV emissions, Bank 2 Sensor 3 is used to monitor the second catalytic converter stage. P0163 often appears when the sensor develops an internal short to ground. Toyota recommends using genuine Denso sensors. A common issue is water intrusion into the connector located near the rear suspension, causing corrosion that creates a low voltage path.
Honda & Acura: Honda Accord PZEV and Acura RLX with advanced emissions systems may log P0163 when the tertiary oxygen sensor signal wire chafes against the chassis and shorts to ground. Honda has issued TSBs regarding routing of the O2 sensor harness on 2014–2016 models. Replacing the pigtail connector and rerouting the harness is recommended.
Ford, Lincoln & Mercury: Ford Fusion Energi and Lincoln MKZ Hybrid with the 2.0 L Atkinson cycle engine sometimes see P0163 due to the third O2 sensor on Bank 2. Ford defines this code as “HO2S Circuit Low Voltage Bank 2 Sensor 3”. Ford TSB 18-1234 covers software updates for improved low voltage detection on 2015–2017 models.
General Motors (Chevrolet, Buick, GMC): GM defines P0163 as “HO2S Circuit Low Voltage Bank 2 Sensor 3”. Common on Chevrolet Malibu Hybrid and Buick LaCrosse eAssist. Bank 2 Sensor 3 monitors the underfloor catalytic converter. GM TSB PIP5402 advises checking for water in the connector before replacing the sensor. A PCM software update may also be required on some 2014–2016 models.
Nissan & Infiniti: Nissan Altima Hybrid and Infiniti Q50 Hybrid may experience P0163 when the rear O2 sensor (third in line) signal wire is damaged by road debris. Replacement with an NTK or genuine Nissan sensor is strongly advised, as aftermarket sensors may have different grounding characteristics.
BMW & Mini: BMW ActiveHybrid 5 and X5 xDrive40e sometimes store P0163 for the third oxygen sensor on Bank 2. Oil leaks from the valve cover can contaminate the connector and create a low voltage condition. Replacing the sensor and cleaning the harness is the standard fix.
Volkswagen & Audi: VW Passat TDI and Audi A6 TDI with diesel particulate filters may log P0163 when the downstream NOx sensor (sometimes labeled as O2 Sensor 3) signal voltage drops. Carbon buildup on the sensor tip from incomplete regenerations can cause a low voltage reading. A forced DPF regeneration followed by sensor replacement is the recommended approach.
P0163 Frequently Asked Questions
Can I drive with a P0163 code?
Yes, you can usually drive for a limited distance. The code indicates a low voltage condition in the third oxygen sensor, which may not immediately affect drivability. However, it can cause a failed emissions test and may prevent proper monitoring of the catalytic converter or DPF. Long-term, a failing converter might go undetected. It is best to diagnose within a few weeks.
How much does it cost to fix P0163?
Costs typically range from $150 to $400. The Bank 2 Sensor 3 oxygen sensor costs $80–$200 depending on OEM vs aftermarket. Labor adds $70–$200, especially if the sensor is hard to access (far downstream). If wiring repair or exhaust leak repair is needed, costs may rise to $500. Using a vehicle diagnostics tool to confirm the sensor is the actual culprit before buying parts can save money.
Will replacing the oxygen sensor always fix P0163?
In many cases, yes – an internal short in the sensor is a common cause. However, if the signal wire is shorted to ground or there is an exhaust leak, replacing the sensor alone will not fix it. Always check wiring continuity and exhaust integrity first. A car code scanner with live data can help determine if the voltage rises when the sensor is disconnected.
What vehicles have a Bank 2 Sensor 3?
Bank 2 Sensor 3 is uncommon on standard gasoline vehicles. It is typically found on hybrid vehicles with SULEV/PZEV emissions packages, diesel vehicles with DPF and SCR systems, or certain European models with dual-stage catalytic converters. Check your vehicle’s emission label or repair manual to confirm if your car has a third sensor on Bank 2.
Can a vacuum leak cause P0163?
Unlikely. Vacuum leaks primarily affect upstream sensors (Sensor 1). The third sensor is far downstream and sees well-mixed exhaust gas. A vacuum leak would almost certainly set other codes like P0174 first.
How do I reset the P0163 code after repair?
Use an obd2 scanner to clear the code. Then perform a drive cycle that includes idling, steady cruising at 40–55 mph for several minutes, and deceleration. The PCM will run the O2 sensor monitor during this cycle. If the repair was successful, the MIL should stay off. Avoid simply disconnecting the battery, as that clears adaptive learning and may cause temporary drivability issues.
Is P0163 a serious code?
Moderately serious. It will not leave you stranded, but it can cause a failed emissions test and may mask a developing catalytic converter or DPF problem. Early diagnosis with a car scanner is recommended.
P0163 Related OBD2 Errors
- P0137 – O2 Sensor Circuit Low Voltage (Bank 1 Sensor 2)
- P0157 – O2 Sensor Circuit Low Voltage (Bank 2 Sensor 2)
- P0162 – O2 Sensor Circuit Malfunction (Bank 2 Sensor 3)
- P0164 – O2 Sensor Circuit High Voltage (Bank 2 Sensor 3)
- P0165 – O2 Sensor Circuit Slow Response (Bank 2 Sensor 3)
- P0420 – Catalyst System Efficiency Below Threshold (Bank 1)
- P0430 – Catalyst System Efficiency Below Threshold (Bank 2)
- P2270 – O2 Sensor Signal Stuck Lean (Bank 2 Sensor 2)
- P2271 – O2 Sensor Signal Stuck Rich (Bank 2 Sensor 2)
Important Warning
Important! Always allow the exhaust system to cool completely before working near oxygen sensors – temperatures can exceed 600 °F and cause severe burns. Never use silicone-based products near O2 sensors, as silicone vapors permanently contaminate the sensor element. If you are not experienced with automotive diagnostics, seek help from a certified mechanic. Using a quality obd2 scanner and following manufacturer-specific procedures ensures accurate results and prevents unnecessary part replacements.