O2 Sensor Circuit No Activity / Slow Response (Bank 1 Sensor 1)
The ECU detects that the upstream oxygen sensor on bank 1 shows no switching activity or responds too slowly to changing exhaust gas composition. Often the sensor is aged, contaminated by silicone or fuel additives, or the heater circuit is degraded.
Affected components
- Oxygen sensor b1s1
- Oxygen sensor heater circuit
- Exhaust manifold gasket
Common causes
- High likelihood: Sensor aged or poisoned (silicone, lead, coolant)
- Medium likelihood: Sensor heater circuit weak
- Medium likelihood: Exhaust leak upstream of sensor diluting reading
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
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.