P0140
O2 Sensor Circuit No Activity Detected Bank 1 Sensor 2
Fuel & air metering (O2 sensor)
Generic OBD-II
Medium
What it means
P0140 means the downstream oxygen sensor on Bank 1 (Sensor 2, after the catalytic converter) shows no switching activity — its signal is flat instead of responding to exhaust changes. This sensor mainly monitors converter health rather than controlling fuel, so the car usually drives normally, but the code will fail an emissions test until the sensor or its wiring is repaired.
Medium
Can I keep driving? Safe to drive short-term — this is the downstream sensor used for catalyst monitoring, so drivability is usually normal, but it will fail an emissions test.
Common symptoms
What you'll notice
- Check-engine light on
- Failed emissions/readiness test
- Little or no change in how the car drives
- Flat, unchanging downstream O2 reading on a scan tool
Common causes
Most likely first
- Failed downstream oxygen sensor (Bank 1, Sensor 2)Likely
- Corroded or damaged wiring/connector at the sensorCommon
- Exhaust leak near the sensor letting in outside airCommon
- Faulty ECM (rare — confirm sensor and wiring first)Less often
How to diagnose & fix
Work through it in order
- View the Bank 1 Sensor 2 signal live — 'no activity' shows as a flat, static voltage.
- Inspect the sensor connector and wiring for corrosion, melting, or damage.
- Check for exhaust leaks upstream of the sensor that can flatten the signal.
- Replace the downstream O2 sensor if the wiring is good and the signal stays inactive.
- Clear the code and drive a full cycle to confirm the sensor now switches.
FAQ
Quick answers
Is it safe to drive with P0140?+
Generally yes. Sensor 2 monitors the catalytic converter rather than controlling fuel, so the car usually drives normally — but it won't pass an emissions test until fixed.
Can I just clear P0140?+
It returns after the next monitor run if the sensor is still inactive. Replace the sensor or fix the wiring/exhaust leak first.
Related codes
Often seen with P0140
Read & clear P0140 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX