P0140 — O2 Sensor Circuit No Activity / Slow Response (Bank 1 Sensor 2)
The ECU detects no switching or excessively slow response from the downstream oxygen sensor on bank 1. Typical for an aged or poisoned sensor; downstream sensors should show a relatively flat signal but must respond to fueling changes during diagnostic monitor runs.
General code reference. Confirm the definition and diagnostic procedure for your vehicle's year, model and engine. A stored code alone does not identify a failed part.
Affected components
- Oxygen sensor b1s2
- Oxygen sensor heater circuit
- Catalytic converter bank1
Possible causes to check
These are possible checks, not a ranked diagnosis. Follow the vehicle manufacturer's test procedure before replacing parts.
- Sensor aged or poisoned
- Sensor heater circuit weak
- Catalytic converter so degraded that downstream signal mirrors upstream
Possible symptoms
- Check engine light on
- Increased fuel consumption
- Possible rough idle or hesitation
- Failed emissions test
Diagnostic notes
- The malfunction indicator lamp may illuminate
- This code can affect emissions
- A drive cycle may be required after repair
Related codes
Sources
Check each reference's vehicle and model-year scope. General background links do not establish which fault is most likely on your vehicle.
Diagnostic information is provided for reference only. Confirm the code with a compatible scan tool and follow the vehicle manufacturer's service procedures before replacing components.