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.

Real-world scan data

Seen in

1,041

scans in the past year

Found in

0.2%

of scans

0.3%

of scans that found faults

Appears alongside · share of P0140 scans

P0160in 15.9% of scans

P0138in 13.1% of scans

P0030in 12.4% of scans

Figures reflect only diagnostic scans recorded through our own apps and tools. Cars are typically scanned because a symptom or warning light prompted it, so these counts describe our scan records — not the incidence of faults in any model, and not the quality, reliability, or safety of any vehicle. No comparison between manufacturers or models is implied. All trademarks belong to their respective owners; no affiliation or endorsement is implied.

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.

Read & clear P0140 yourself

Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.

▶ Get it on Google Play

✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX