P0137 — O2 Sensor Circuit Low Voltage (Bank 1, Sensor 2)

P0137 means the downstream oxygen sensor on bank 1 is stuck at low voltage. Because sensor 2 sits after the catalyst, this is usually the sensor or its wiring rather than a fuel mixture problem.

Cost range: $120–$450. Severity: low. Safe to drive? Yes. This is an emissions monitoring fault, not a driveability one.

Most common causes of P0137

1. Failed downstream O2 sensor — Most likely cause on a high-mileage car. ($120–$400)
2. Exhaust leak between catalyst and sensor — Fresh air keeps the reading pinned low. ($100–$400)
3. Damaged sensor wiring — Road debris and heat take out the under-car harness. ($80–$250)

Symptoms drivers report with P0137

• Check engine light
• Failed emissions test
• No driveability change