What it means
The downstream oxygen sensor signal is fixed at a low voltage. Either the catalyst is letting unburned oxygen through (sensor sees lean), the sensor itself is shorted to ground, or the catalyst is so degraded that the downstream signal mirrors a lean upstream condition.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
Bank 1 Sensor 2 is the oxygen sensor after the catalytic converter, where it reports the oxygen level in the exhaust leaving the catalyst. The control module sets this code when that sensor's signal stays below the expected range, which can result from a lean exhaust reading or a signal circuit pulled low.
Common causes
Most likely first.
- Signal wire shorted to ground
- Oxygen sensor failed
- Exhaust leak near the downstream sensor
Symptoms
- Check engine light on
- Failed emissions test
How to diagnose it
- Record freeze-frame data and check when P0137 set, including engine temperature and fuel-control status.
- Inspect Bank 1 Sensor 2 and its wiring for exhaust damage, a signal wire touching ground, loose pins, or corrosion.
- Check for an exhaust leak near the downstream sensor that could draw in outside air and produce a lean reading.
- Use a scan tool to compare the downstream sensor signal with the Bank 1 upstream sensor and fuel-trim data once the engine is warm.
- Test the Bank 1 Sensor 2 signal circuit for a short to ground and verify sensor operation against the wiring diagram and manufacturer's specification.
Common fixes
- Repair a signal wire shorted to ground or damaged near the exhaust.
- Repair an exhaust leak close to Bank 1 Sensor 2.
- Clean or repair corroded or loose connector terminals.
- Replace the Bank 1 Sensor 2 sensor if circuit checks pass but its signal remains low.
Can I keep driving?
The vehicle may drive normally, but emissions monitoring can be impaired and it may fail an emissions test. Avoid ignoring the light; if the engine begins running poorly or the light flashes, stop driving and investigate promptly.
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.