What it means
Same condition as P0131 but on bank 2. The upstream sensor sees a continuously lean exhaust on bank 2 or has a signal short to ground.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
Bank 2 Sensor 1 is the upstream oxygen sensor that reports exhaust oxygen for Bank 2 fuel control. P0151 sets when its signal voltage stays lower than expected; this can reflect genuinely lean exhaust or a signal circuit pulled toward ground.
Common causes
Most likely first.
- Exhaust leak upstream of the sensor
- Bank 2 running lean (vacuum leak, fuel pressure)
- Connector pins corroded - high contact resistance
Symptoms
- Check engine light on
- Increased fuel consumption
- Possible rough idle or hesitation
- Failed emissions test
How to diagnose it
- Record freeze-frame data and compare Bank 2 Sensor 1 live readings with fuel trims and the other bank to see whether Bank 2 appears genuinely lean.
- Inspect for exhaust leaks ahead of the upstream Bank 2 sensor and for intake or vacuum leaks affecting that bank.
- Check the Bank 2 Sensor 1 connector for corrosion, pushed-back pins, and poor contact, then inspect its harness for damage.
- If live data supports a lean condition, investigate Bank 2 fuel delivery and other causes of lean running before replacing the sensor.
- Test the signal circuit for a short to ground and verify sensor operation using the manufacturer's procedure.
Common fixes
- Repair an exhaust leak upstream of Bank 2 Sensor 1.
- Repair a vacuum leak or other confirmed cause of lean running on Bank 2.
- Clean or repair corroded or poorly seated connector terminals.
- Repair a signal wire short to ground or replace the sensor if testing identifies it as faulty.
Can I keep driving?
A short gentle drive may be possible if the engine runs normally, but a true lean condition can cause rough running and, if severe, engine damage. Avoid hard acceleration and stop if the engine misfires or loses power.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.