P0163
O2 Sensor Circuit Low Voltage (Bank 2 Sensor 3)P0163 is a generic OBD-II powertrain diagnostic trouble code: O2 Sensor Circuit Low Voltage (Bank 2 Sensor 3). It is logged by the engine control unit when the o2/lambda monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.
What P0163 means
P0163 is set when the PCM detects that the Bank 2, Sensor 3 oxygen sensor signal is stuck at an abnormally low voltage — typically below approximately 0.1 V — for longer than the calibrated fault timer. A healthy downstream O2 sensor should hover in the 0.5–0.8 V range after the catalytic converter has fully processed the exhaust, producing only minor, slow fluctuations. A persistently low voltage indicates either that the sensor cannot generate sufficient output (open signal path, internal fault) or that the exhaust chemistry is genuinely extremely lean at that point.
The 'low voltage' designation distinguishes P0163 from the broader 'circuit malfunction' of P0162. Both codes concern Bank 2 Sensor 3, but P0163 specifically identifies a signal that is measurably present but biased toward zero volts, rather than absent entirely. Common hardware causes include an open circuit on the signal wire (which can pull the line to ground through the ECM's internal bias), an internally shorted sensor element, or a genuine lean exhaust condition caused by a large exhaust leak introducing air downstream of the catalyst.
As with all third-sensor codes, B2S3 is present only on vehicles with dual catalytic converters in series, certain Y-pipe layouts, or similar multi-catalyst configurations — it is not a universal fitment. The sensor does not drive active fuel trim, so drivability impact is usually minimal, but the MIL will remain illuminated and catalyst monitoring for Bank 2 will be suspended until the fault is resolved.
Common causes
Most-frequently reported root causes when P0163 is logged.
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1
Open circuit on the signal wire — the ECM's internal pull-down bias holds the line low when the sensor cannot source any current.
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2
Failed sensor element with an internal short — the zirconia cell has degraded and pulls its own output toward ground.
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3
Exhaust leak downstream of the second catalyst introducing ambient air — false lean reading holds voltage below 0.1 V.
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4
Corroded or damaged sensor connector — high contact resistance or broken signal terminal presents as a low-voltage open circuit.
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5
Contaminated sensor element (oil, coolant, or carbon deposits) — severely degraded output that cannot rise above the low threshold.
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6
Vacuum leak on the Bank 2 intake driving genuine lean combustion — the sensor correctly reports a lean condition that is real, not a sensor fault.
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7
Harness wiring shorted to ground — a chafed signal wire contacting the chassis or exhaust system pulls the signal to 0 V.
Symptoms drivers notice
How to diagnose P0163
A typical diagnostic flow when this code is present.
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1
Connect a scan tool and record P0163 freeze-frame data; note the sensor voltage value logged at the time of the fault — confirm it is at or near 0 V.
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2
With the engine warm, view B2S3 live data; if the voltage is fixed at 0 V or below 0.1 V and does not respond even to a brief rich snap of the throttle, the sensor or its signal circuit is at fault.
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3
Inspect the sensor connector and wiring harness from the sensor back toward the PCM for chafing, melted insulation, or corrosion; pay particular attention to areas where the harness routes near exhaust components.
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4
With the sensor disconnected, use a multimeter to check the signal wire for continuity and short-to-ground; a wire shorted to chassis will read near 0 Ω to ground.
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5
Check for exhaust leaks downstream of the second catalytic converter — a crack, loose clamp, or failed gasket near the sensor position can admit ambient air and produce a genuine low-voltage reading.
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6
Disconnect the sensor and measure the sensor's internal resistance between the signal and ground pins; an abnormally low reading (less than a few hundred ohms) suggests an internal short in the element.
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7
Replace the sensor if wiring and exhaust integrity are confirmed good; verify after a full warm drive cycle that the signal now reads in the normal 0.5–0.8 V range at steady cruise.
Related powertrain codes
- P0040 — Upstream Oxygen Sensors Swapped From Bank To Bank
- P0041 — Downstream Oxygen Sensors Swapped From Bank To Bank
- P0130 — O2 Sensor Circuit Malfunction (Bank 1 Sensor 1)
- P0131 — O2 Sensor Circuit Low Voltage (Bank 1 Sensor I)
- P0132 — O2 Sensor Circuit High Voltage (Bank 1 Sensor 1)
- P0133 — O2 Sensor Circuit Slow Response (Bank 1 Sensor 1)
Frequently asked questions
What is the difference between P0162 and P0163?
Both codes refer to Bank 2 Sensor 3, but P0162 is a general 'circuit malfunction' (signal out of range or inactive in any direction), while P0163 specifically identifies a 'low voltage' condition where the signal is confirmed stuck below the lower threshold of approximately 0.1 V. P0163 narrows the diagnosis toward open-circuit or sensor failures that pull the line low rather than high.
Can an exhaust leak cause P0163?
Yes. If there is a crack or loose joint downstream of the catalytic converter near the sensor, ambient air is drawn into the exhaust under vacuum pulses, creating a genuinely lean oxygen reading. The sensor may be working perfectly and accurately reporting the lean condition. Always inspect the exhaust system before replacing the sensor.
Could a vacuum leak trigger P0163?
Indirectly, yes. A large vacuum leak on the Bank 2 intake causes the engine to run lean, which the upstream sensor (B2S1) reports to the PCM. If the lean condition is severe enough that even the post-cat exhaust on Bank 2 remains oxygen-rich, B2S3 will read low voltage correctly. Upstream fuel trim codes (P0171/P0174) would likely accompany P0163 in this scenario.
Will clearing the code make P0163 go away permanently?
No. If the underlying fault — whether a damaged wire, failed sensor, or exhaust leak — is not repaired, the PCM will detect the same low-voltage condition again after the drive-cycle monitoring period elapses and re-set the code. Clearing codes without fixing the root cause only delays diagnosis.
Disabling P0163 in software
RaceTune can permanently disable P0163 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.
Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.
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