P2A3BO2 Sensor Negative Current Control Circuit/Open Bank 1 Sensor 3
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- How the car detects it
- P2A3B points to a break in the negative current control line of wide-band sensor 3 on bank 1, the common return of pump and Nernst cell. Bosch calls it virtual ground (IPN/VM, pin 2 on the LSU 4.9), NTK names it COM; the controller holds it at a bias of about 2.5 V, as Saab's 2010 9-5 shows at the plug, so current can flow both ways. No manufacturer documents P2A3B publicly. On the upstream analog P2251, Ford tells an open return from an open pump lead because lambda still shifts during reference-current pulses, and it flags a sensor voltage parked inside a band of 1.45–1.55 V, allowing 10 s before the fault is stored. P2A3C/P2A3D are low/high, P2A38 is the open pump lead. Expect the lamp, not a drivability change.
- What you may notice
- Check engine light
- Sensor 3 signal stuck around its mid voltage in live data
- Catalyst or aftertreatment monitor not completed
- Likely causes
- LikelyBroken virtual-ground wire or loose pin in the sensor plug
- PossibleCorroded terminals in the connector near the rear exhaust
- RareInternal break of the common electrode inside the probe
- 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: €0 – €450
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.