P2A01O2 Sensor Circuit Range/Performance Bank 1 Sensor 2
- 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
- Sensor 2 on bank 1 sits behind the catalytic converter and mainly serves to judge how well the converter stores oxygen. Ford uses P2A01 for a signal that is out of range on the low side: on petrol engines with certain Continental control modules from 2011, and still in its 2020–2023 summary, a reading under −0.2 V lasting 10 s sets the code, usually because signal and return wires are swapped or the sensor is worn. On diesels this position is often taken by a NOx sensor with an oxygen output: Ford checks it against a calculated oxygen level, and GM's 2025 diesel tables let it differ from sensor 1 by at most 6 % at full load (120 of 240 samples, Type B). Mazda's CX-9 bulletin SA-004/19 links it to engine oil inside connector C-34 from a leaking oil pressure switch.
- What you may notice
- Check engine light on
- Catalyst or aftertreatment monitor stays incomplete
- Usually no noticeable change in driving behaviour
- Likely causes
- LikelyDownstream sensor worn or contaminated
- PossibleEngine oil or moisture in the sensor connector (Mazda CX-9 connector C-34)
- PossibleSignal and return wires swapped, e.g. after a sensor replacement
- PossibleOn diesels, oxygen output of the second NOx sensor drifting
- 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 – €450
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.