P2A08O2 Sensor Negative Voltage 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
- P2A08 is the negative-voltage fault of the third oxygen sensor on bank 1, which sits behind a second converter or another aftertreatment stage. Such a sensor is normally a zirconia switching type whose output should stay above zero; an intact, correctly wired sensor does not deliver a negative reading in normal operation, so the code suggests swapped leads, a short between the signal return and another circuit, or a cracked element. No manufacturer documents P2A08 publicly; this description rests on CARB's duty to catch open circuits and readings outside the valid band, on Ford's −0.2 V limit for rear sensors (stored there under range codes) and on a Denso patent for crack detection. Sensor 3 hardly influences mixture control, so the main consequence is an incomplete converter monitor.
- What you may notice
- Check engine light on
- Converter monitor readiness missing
- Normal driving behaviour in most cases
- Likely causes
- LikelySignal return shorted to another circuit or leads swapped
- PossibleCracked sensing element of sensor 3
- RareFault in the module's sensor input stage
- 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: €60 – €350
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.