Lambda / O₂ — Narrow Band

What it tells you

A healthy narrow-band oxygen sensor swings briskly between rich (~0.8V) and lean (~0.1V) as the ECU corrects fuel trim. A scope exposes lazy switching, a stuck-rich bias, or a flat-lined sensor — the difference between a fault and a clean bill of health.

Healthy vs fault

Toggle Fault overlay on the scope above to drop the faulty capture over the healthy one. Seeing both traces on the same graticule is how you train your eye for the difference — the deviation that names the fault.

Symptoms this catches

• ▸lean
• ▸rich
• ▸fuel trim
• ▸emissions fail
• ▸lazy o2
• ▸cat efficiency

Watch the walkthrough