P0140 Code: O2 Sensor No Activity (B1S2) — Causes & Fix
P0140 means the downstream oxygen sensor (bank 1, sensor 2) shows no activity — the ECM sees a flat, unresponsive signal.
- Applies to
- All OBD-II vehicles (any make or model)
- Est. repair cost
- $40 – $300
- Time to fix
- 30 minutes – 2 hours
What it means
Causes include a dead downstream O2 sensor, an open in its wiring, or a heater/fuse fault. P0140 is a generic OBD-II powertrain code defined in the SAE J2012 standard, so it applies to virtually any 1996-or-newer petrol car or light truck regardless of make. Fix the underlying fault, then clear the code with an OBD-II scan tool — it will return if the problem isn't resolved.
Symptoms
- Check engine light on
- Little drivability effect
- Blocks emissions readiness
How to fix it
- 1
Check wiring and heater fuse
1. Inspect the connector and wiring. 2. Confirm the O2 heater fuse.
- 2
Replace the sensor
1. Replace an inactive downstream O2 sensor. 2. Clear the code.
Frequently asked questions
Is P0140 urgent?
Drivability is usually fine, but it prevents the emissions monitor from completing, so fix it before an inspection.
Last updated July 19, 2026
Guidance only — always consult a qualified professional or the official service manual before carrying out repairs.