P2A06O2 Sensor Negative Voltage Bank 1 Sensor 1
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- P2A06 means the switching oxygen sensor ahead of the converter on bank 1 is delivering a voltage below zero. A zirconia sensor generates its voltage from the oxygen difference between exhaust gas and reference air, normally about 0.1–0.9 V; a negative value means the exhaust side looks richer in oxygen than the reference side, or the polarity at the module is reversed. No manufacturer documents this code publicly. A Denso patent uses exactly this symptom during fuel cut-off, with a time counter, to detect a cracked sensing element; Ford watches for rear-sensor readings under −0.2 V but stores them as P2A01/P2A04. The code only makes sense for switching sensors – many current engines use wide-range sensors in this position. Fuel control loses its feedback.
- What you may notice
- Check engine light on
- Mixture control falls back to open loop, consumption rises
- Possible rough idle or poor emissions result
- Likely causes
- LikelyCracked ceramic element, for instance after water shock or impact
- PossibleSignal and signal-return wires swapped at connector or after a repair
- RareReference air path of the sensor contaminated by oil, sealant or water
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Easy · Often possible to do yourself.Typical cost: €60 – €300
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.