P2096
Post Catalyst Fuel Trim System Too Lean (Bank 1)
Long-term fuel trim derived from the downstream oxygen sensor on bank 1 has reached the lean limit. The downstream-trim correction is a fine adjustment that runs after the main trim from the upstream sensor; persistent excursion suggests a degraded catalyst, an exhaust leak after the catalyst, or a drifting downstream sensor.
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: medium
Symptoms
- Check engine light on
- Failed emissions inspection
- Possibly slightly increased fuel consumption
- Sulfur (rotten egg) smell from exhaust under load
Common causes
Ordered by how often each turns out to be the cause.
- Exhaust leak after catalyst (post-cat sensor sees ambient air)Common
- Downstream sensor driftingPossible
- Catalyst lightly degradedLess likely
Parts involved
- Oxygen Sensor Downstream
- Catalytic Converter
- Exhaust Pipe Post Cat
P2096 is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.