P2A02O2 Sensor Circuit Range/Performance Bank 1 Sensor 3
- 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 3 on bank 1 follows a second converter or, on diesels, a further aftertreatment stage. GM is the only maker found that documents P2A02: in its 2025 diesel tables the oxygen value of the third NOx sensor is held against that of sensor 2 while the engine runs at full load, and a gap of more than 6 % in either direction in 120 of 240 samples sets a two-trip Type B fault. The test only starts once both sensors report themselves fully operational and the sensor-2 check has run, so a fault further upstream shows up as P2A01 first. For petrol engines with a third sensor no public description of this code exists; there CARB's rule applies that downstream sensors must stay good enough for converter monitoring. A drifting sensor 3 hardly changes how the car drives but stops the aftertreatment checks.
- What you may notice
- Check engine light on
- Aftertreatment monitor does not complete
- No noticeable effect on driving in most cases
- Likely causes
- LikelyOxygen output of the third NOx or oxygen sensor drifting with age
- PossibleExhaust leak between sensor 2 and sensor 3 lets outside air in
- RareSensor coated with soot, ash or urea deposits
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Often possible to do yourself.Typical cost: €100 – €600
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.