P2A08
O2 Sensor Negative Voltage Bank 1 Sensor 3
The ECM detects a negative voltage on the signal line of oxygen sensor 3 on bank 1. This is unusual for narrow-band sensors and often indicates a short to a negative reference, ground offset, or a wide-band sensor wired incorrectly.
- 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.
- Signal wire shorted to negative referenceCommon
- Ground offset between sensor and ECMPossible
Parts involved
- Oxygen Sensor B1s3
- Wiring Harness
- ECM
P2A08 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.