P2A10 O2 Sensor Negative Voltage Bank 2 Sensor 2

The downstream oxygen sensor of bank 2, behind that bank's converter, is reporting a negative voltage. Bank 2 only exists on V and flat engines. A healthy switching sensor swings between roughly 0.1 and 0.9 V; readings below zero come from swapped signal and return wires, for instance after splicing in a universal sensor, from a fouled reference air path or from a cracked ceramic. No manufacturer documents P2A10 publicly. Ford monitors precisely this condition on rear sensors with a limit of −0.2 V held over 10 s but stores P2A04 for bank 2. A Denso patent treats negative readings during fuel cut-off as a sign of an element crack. The engine itself runs normally, but converter monitoring on bank 2 is blocked until the cause is fixed.

Likely causes

Symptoms

• Check engine light on
• Catalyst monitor of bank 2 not ready
• No change in driving behaviour

Repair estimate

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

Related codes

References: law.cornell.edu, newtonnet.co.uk, patents.google.com.