P2A08: O2 Sensor Negative Voltage Bank 1 Sensor 3
Standardized SAE J2012 code · P2Axx codes
What does P2A08 mean?
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.
The code tells you which monitor failed, not which part is broken. Test before replacing parts.
Symptoms
- Check engine light on
- Increased fuel consumption
- Possible rough idle or hesitation
- Failed emissions test
Common causes
- High Signal wire shorted to negative reference
- Medium Ground offset between sensor and ECM
Likelihood is a general estimate across vehicles; your make and model may differ.
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