Powertrain
generic / SAE
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.
SystemPowertrain
Typegeneric / SAE
GroupP2
Range / number– / 96
Possible causes
- Exhaust leak after catalyst (post-cat sensor sees ambient air) high
- Downstream sensor drifting medium
- Catalyst lightly degraded low
Symptoms
- Check engine light on
- Failed emissions inspection
- Possibly slightly increased fuel consumption
- Sulfur (rotten egg) smell from exhaust under load
Inspection / repair
- Difficulty: medium
- DIY: possible
- Estimated cost: 60–700 €
- Estimated time: 0.5–4 h
- Component: oxygen sensor downstream
- Component: catalytic converter
- Component: exhaust pipe post cat
- MIL / check engine light
- emissions-relevant
- drive cycle required
Sources
References
sae:J2012