P0137Powertrain
Powertrain · SAE
O2 Sensor 2 (Bank 1) — Low Voltage
Meaning
The downstream oxygen sensor (bank 1, sensor 2) reports a constantly low voltage. This sensor monitors catalytic converter efficiency, so the abnormal reading corrupts that monitoring.
Common causes
- Faulty or aged downstream sensor
- Short to ground or damaged wiring
- Exhaust leak near the sensor
- Corroded connector
- Degraded catalytic converter altering the signal
Symptoms
- Check engine light on
- Catalyst efficiency monitors not completing
- Slightly increased fuel consumption
- No obvious driveability loss in mild cases
Severity
Mild/moderate: rarely affects driveability but blocks the emissions monitors and can fail an inspection.
What to do
- Compare the downstream sensor signal with the upstream one
- Inspect wiring, connector and any exhaust leaks
- Check the catalytic converter state if the sensor is healthy
- Replace the downstream sensor if the signal stays low