OBD-II Code · Sensors
P0140
O2 Sensor No Activity (B1S2)
Severity
low
Lowest on our scale. Fix it when convenient.
Can you drive it
Only if running normally
A short trip to a shop may be reasonable if the light is steady and the car runs normally. Stop safely for a flashing light, severe shaking, overheating, loss of power, or another urgent warning. The code alone cannot confirm safety.
Indicative cost (USD)
$150–$400
Varies by vehicle, diagnosis, parts, and local labor. This is not a repair quote.
Downstream sensor flatlined.
How a shop works this
Work from evidence to part, not the other way round. A code names a circuit or a symptom; it does not name the part that failed.
Note every code that is set, not just this one.
Codes that appear together usually narrow the cause faster than any one of them read alone.
Read the freeze frame — the conditions the fault was recorded under.
Cold or warm, idle or load, road speed and engine speed. A fault that only appears cold is a different fault from one that only appears under load, even with the same code on the scanner.
Confirm the fault is current rather than history.
Clear the code and see whether it returns under those same conditions. A code that does not come back may have been logged during a repair, a flat battery, or a bad connection that has since been disturbed.
Then work the likely-causes list in the order shown.
That order is what a shop checks first for this code — wiring and connections before the component they run to, because a connector costs nothing to inspect and is a common answer.
If the code comes back after a repair, the underlying fault is still there. That is the point to bring in a scanner with live data and freeze-frame, or a shop that has one.
Common symptoms
- Check engine light
Likely causes
- Dead sensorMost common
- Disconnected harness
Read the full diagnostic procedureP0140 means bank 1 downstream sensor (B1S2) shows NO activity — the signal sits flat at bias voltage and never moves, even under conditions (decel fu…
P0140 means bank 1 downstream sensor (B1S2) shows NO activity — the signal sits flat at bias voltage and never moves, even under conditions (decel fuel cut, throttle snap, cat-monitor test) where a working downstream sensor should show some movement. Like P0134 upstream, this often pairs with a heater fault (P0141), because a cold sensor produces no signal at all.
Cheapest-first
- ohm the heater pins (spec 6-15 ohms narrow-band cold) — open circuit means sensor heater failed.
- If heater is in spec, verify the ECU is providing bias voltage (key-on engine-off, ~0.45V at the signal pin).
- If bias is there but no activity once warmed up, the element is dead.
- Note that on cars with cylinder-deactivation or aggressive lean-burn modes (GM AFM, Honda VCM, Chrysler MDS), the downstream may legitimately sit quieter than the upstream and the ECU has wider tolerance — so a P0140 only sets when the signal is truly inert.
Vehicle-specific patterns2004-2008 Ford F-150 5.4L 3V throws P0140 routinely past 120k miles — Motorcraft downstream sensors degrade in cold-weather salt environments.
- 2004-2008Ford F-150 5.4L 3V throws P0140 routinely past 120k miles — Motorcraft downstream sensors degrade in cold-weather salt environments.
- 2006-2013Chevy Impala / Malibu 3.5L/3.9L sets P0140 when the downstream harness chafes against the catalytic converter shield.
- 2005-2012Toyota Avalon / Sienna 2GR-FE throws P0140 after a cylinder-deactivation event damages the downstream element with quench.
- 2007-2014Nissan Murano / Pathfinder VQ35 sets P0140 from a TSB-noted Bosch sensor lot (Nissan campaign extended warranty on affected VINs). Cost band: $150-$350 for sensor + labor; under $80 if it's a chafed wire repair.
Look up another code
P0140 — frequently asked
What does a P0140 code mean?
Downstream sensor flatlined.
What causes a P0140 code?
Common causes: Dead sensor; Disconnected harness.
What are the symptoms of a P0140 code?
Typical symptoms: Check engine light.
Is it safe to drive with a P0140 code?
Only if running normally. A short trip to a shop may be reasonable if the light is steady and the car runs normally. Stop safely for a flashing light, severe shaking, overheating, loss of power, or another urgent warning. The code alone cannot confirm safety. Estimated repair: $150-$400.
How do I diagnose a P0140 code?
Work from evidence to part, not the other way round. A code names a circuit or a symptom; it does not name the part that failed. 1. Note every code that is set, not just this one. 2. Read the freeze frame — the conditions the fault was recorded under. 3. Confirm the fault is current rather than history. 4. Then work the likely-causes list in the order shown.
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