O2 Sensor Signal Biased/Stuck Lean Bank 1 Sensor 4
Bank 1 sensor 4 O2 sensor signal is biased low — sensor stuck reading lean regardless of true mixture. A drifted or sluggish lambda sensor lets the mixture run lean or rich without correction — fuel economy and emissions suffer immediately.
Affected components
- Oxygen sensor b1s4
Common causes
- High likelihood: Sensor aged or contaminated
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
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.