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.
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.
Common causes
- high
Signal wire shorted to negative reference
One of the most commonly reported causes for this code — check this first.
Typical part cost: $110-660
- medium
Ground offset between sensor and ECM
A plausible cause — test and verify before replacing parts.
Typical part cost: $110-660
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First things to check
- 1Confirm the code with a scan tool and check for additional related codes.
- 2Inspect the relevant sensors, wiring, and connectors for damage or corrosion.
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Related codes
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Frequently asked questions
What does P2A09 mean?
P2A09 means "O2 Sensor Negative Voltage Bank 2 Sensor 1". It is a generic OBD-II code that points to a fault in the auxiliary emission controls.
What are the most common causes of P2A09?
signal wire shorted to negative reference; ground offset between sensor and ecm — these are the most commonly reported causes. Verify with a proper diagnosis before replacing parts, or use the Wrenchify app for a vehicle-specific diagnosis.
Can I keep driving with this code?
The vehicle is usually drivable for short distances, but the problem can worsen or affect emissions. Diagnose and repair as soon as practical. Use the Wrenchify app for a full diagnosis specific to your vehicle.
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