OBD-II code · Powertrain (generic, extended)
P2A09 O2 Sensor Negative Voltage Bank 2 Sensor 1
The ECM detects a negative voltage on the signal line of oxygen sensor 1 on bank 2. 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.
Is it safe to drive with P2A09?
Usually safe to drive in the short term. Get it diagnosed when convenient, sooner if the car drives differently.
Common causes
- Most likelySignal wire shorted to negative reference
- PossibleGround offset between sensor and ECM
Symptoms
- Check engine light on
- Increased fuel consumption
- Possible rough idle or hesitation
- Failed emissions test
Repair at a glance
- Difficulty
- Medium
- DIY friendly
- Best left to a mechanic
- Typical labour
- 0.5–3 h
- Emissions test
- Likely to fail
- After the fix
- A drive cycle is needed before the light stays off
- Parts involved
- Oxygen Sensor B2s1, Wiring Harness, Ecm
Related codes
- P2A08O2 Sensor Negative Voltage Bank 1 Sensor 3
- P2A10O2 Sensor Negative Voltage Bank 2 Sensor 2
- P2A11O2 Sensor Negative Voltage Bank 2 Sensor 3
- P2A06O2 Sensor Circuit Range/Performance Bank 1 Sensor 4
- P2A07O2 Sensor Circuit Range/Performance Bank 2 Sensor 4
- P2A0AManifold Absolute Pressure Sensor B Circuit
- P2A0BManifold Absolute Pressure Sensor B Circuit Range/Performance
- P2A0CManifold Absolute Pressure Sensor B Circuit Low
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.