P2A10: O2 Sensor Negative Voltage Bank 2 Sensor 2
What to do
The car will usually drive normally with worse economy. This is nearly always wiring or an earth rather than the sensor — ask for the sensor's ground path and its connector to be checked before a new sensor is fitted, because a new one on the same fault reads exactly the same.
What this code means
The oxygen sensor on bank 2, position 2 is reporting a negative voltage.
A negative voltage from an oxygen sensor is not a reading — it is a symptom of the wiring, and knowing that saves a sensor.
A conventional zirconia oxygen sensor is a battery. It generates its own voltage — roughly 0.1 to 0.9 volts — by comparing exhaust oxygen against outside air, and the chemistry that produces it can only produce a positive voltage. There is no condition of the engine that makes a real sensor read below zero.
So a negative reading means the module is not seeing what the sensor is producing. The two ordinary causes are both wiring. A signal wire shorted to a sensor of the opposite bank or to another circuit can pull the reference below ground. And a poor sensor earth does it directly: the sensor's low side floats above the module's ground, so the difference the module measures goes negative.
That earth path is the one worth checking first, because on many engines the sensor grounds through its own body into the exhaust — so corrosion at the boss, or an exhaust that has been replaced with a poorly bonded section, produces exactly this. The sensor is usually fine.
Which makes this a code where the obvious repair is the wrong one. A new sensor on the same faulty earth reads negative too, and the second one gets blamed on quality.
Likely causes
Start here
- Corroded earth connection · moderate
- Corroded or loose connector · specialist
- Wiring shorted to ground · specialist
Less common
- Faulty oxygen sensor · specialist
- Damaged wiring harness · specialist
Symptoms
Components involved
Information, not instruction
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Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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