P2AC5
Intake Air O2 Sensor Reference Voltage Circuit Low Bank 2
The reference voltage supplied to the intake air oxygen sensor on bank 2 reports a low condition. Lambda measurement on the intake side is unreliable.
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: medium
Symptoms
- Check engine light on
- Increased fuel consumption
- Possible rough idle or hesitation
- Failed emissions test
Common causes
Ordered by how often each turns out to be the cause.
- Reference wire shorted to groundCommon
- Internal short in sensor referencePossible
- Connector pins corroded - high contact resistanceLess likely
Parts involved
- Intake Air O2 Sensor B2
- Wiring Harness
- ECM
P2AC5 is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.