P2A04O2 Sensor Circuit Range/Performance Bank 2 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 2 is the oxygen sensor behind that bank's catalytic converter, used for converter monitoring and fine mixture trim. Ford documents P2A04 together with P2A01 for certain Continental control modules on petrol engines from 2011, and again in its 2020–2023 summary: a rear-sensor voltage that stays below −0.2 V over 10 s sets the code – a value an intact switching sensor should not produce, normally pointing to swapped signal and return wires or a worn sensor. Mazda's CX-9 (2007–2015) logs P2A04 for the left-hand downstream sensor, often together with P2272; bulletins SA-004/18 and SA-004/19 send the technician to look for oil from a leaking oil pressure switch in connector C-34 before replacing the sensor. Driveability rarely suffers, but converter monitoring on bank 2 stops.
- What you may notice
- Check engine light on
- Often stored together with a stuck-lean code for the same sensor
- Catalyst monitor of bank 2 not ready
- Likely causes
- LikelyOil in the sensor connector from a leaking oil pressure switch (Mazda CX-9)
- LikelyDownstream sensor on bank 2 worn
- PossibleSignal and return wires swapped or sensors of both banks plugged in crosswise
- 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: €40 – €350
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.