P2A07O2 Sensor Negative Voltage 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 is the switching oxygen sensor behind the converter; P2A07 says its output has dropped below zero volts. Because the voltage comes from the oxygen difference across the zirconia element, a negative value points to reversed signal and return wires, a contaminated reference air path or a cracked element. No manufacturer documents P2A07 publicly. The closest documented test is Ford's: from 2011 a rear sensor held below −0.2 V for 10 s, put down to swapped wires or sensor degradation – Ford, however, files it as P2A01. A Denso patent watches for a negative output in overrun shut-off, a phase in which the exhaust behind the converter is almost pure air, to find element cracks. As long as the signal is negative, the converter cannot be assessed and the downstream trim switches off.
- What you may notice
- Check engine light on
- Catalyst monitor of bank 1 not ready
- Usually no noticeable change while driving
- Likely causes
- LikelySignal and return wires swapped, e.g. after fitting a universal sensor
- PossibleCracked sensing element
- PossibleSensor degraded or reference air contaminated
- 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: €50 – €250
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.