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P0140: O2 Sensor Circuit No Activity Detected (Bank 1 Sensor 2)
Severity: Low With a steady light and normal running, arrange diagnosis soon. Stop for a flashing light, severe misfire, overheating, or a glowing catalyst; do not assume those symptoms are only a sensor fault.
What does P0140 mean?
The bank 1 downstream oxygen-sensor signal shows no expected activity during monitoring. This can reflect a dead sensor, a heater problem preventing warm-up, or an interrupted signal circuit.
Generic OBD-II definition: O2 Sensor Circuit No Activity Detected (Bank 1 Sensor 2). Confirm applicability in your vehicle service information.
Common causes
- Open or shorted sensor signal wiring
- Failed or contaminated downstream sensor
- Heater failure or water in the connector
Symptoms
- Steady check engine light
- Usually normal engine feel
- Catalyst readiness may be affected
Diagnostic focus
A rear sensor may be quiet when the catalyst is working well. Confirm the specified no-activity test conditions before deciding that a flat graph proves the sensor or converter is bad.
Can I keep driving with P0140?
Severity: Low With a steady light and normal running, arrange diagnosis soon. Stop for a flashing light, severe misfire, overheating, or a glowing catalyst; do not assume those symptoms are only a sensor fault.
If the check engine light is flashing or the car runs badly, stop driving and have it checked.
Typical fixes
- Allow full warm-up and inspect related heater codes
- Inspect the rear harness for melted insulation
- Verify supply/return and sensor response using factory tests
Related codes
O2 Sensor Circuit (Bank 1 Sensor 2)P0139
O2 Sensor Circuit Slow Response (Bank 1 Sensor 2)P0141
O2 Sensor Heater Circuit (Bank 1 Sensor 2)
Sources & review
Definitions and diagnostic background checked 2026-11-06. Generic guidance, not a substitute for the service procedure for your exact year, engine, and transmission.