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.
Medium severity. Can I keep driving?Yes, you can normally drive in moderation, but get it repaired soon: you will use more fuel and the catalytic converter can be damaged over time.
Bank 1 is the side of the engine with cylinder 1. Inline engines only have this bank.
Symptoms
- Check engine light
- Sensor 3 signal stuck around its mid voltage in live data
- Catalyst or aftertreatment monitor not completed
Most likely causes
- Broken virtual-ground wire or loose pin in the sensor plug
- Corroded terminals in the connector near the rear exhaust
- Internal break of the common electrode inside the probe
What to check, in order
Start with the simplest. You can tick off each step.
Good to know
- Repair difficulty: medium
- It affects emissions.
What each character of P2A3B means
- P: Powertrain: engine and transmission
- 2: Generic code: same on every make
- A: Hybrid or air and fuel
- 3B: Specific fault in that system
Frequently asked questions
Can I keep driving with code P2A3B?
Yes, you can normally drive in moderation, but get it repaired soon: you will use more fuel and the catalytic converter can be damaged over time.
What causes code P2A3B?
The most common causes are: broken virtual-ground wire or loose pin in the sensor plug; corroded terminals in the connector near the rear exhaust; internal break of the common electrode inside the probe.
Related codes
- P2A3CO2 Sensor Negative Current Control Circuit Low Bank 1 Sensor 3
- P2A3DO2 Sensor Negative Current Control Circuit High Bank 1 Sensor 3
- P2A38O2 Sensor Positive Current Control Circuit/Open Bank 1 Sensor 3
- P22B2O2 Sensor Negative Current Control Circuit/Open (Bank 1 Sensor 2)
- P2251O2 Sensor Negative Current Control Circuit/Open (Bank 1 Sensor 1)
- P0142O2 Sensor Circuit Bank 1 Sensor 3
Sources
- newtonnet.co.uk: fordobd2012
- saabwisonline.com: dtc p2237 p2239 p2243 p2251 or p2626
- bosch-motorsport.com: Data Sheet 69034379 Lambda Sensor LSU 4.9
- law.cornell.edu: 13 CCR 1968.2
Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.