P2097Post Catalyst Fuel Trim System Too Rich (Bank 1)
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- P2097 is the opposite limit of the post-catalyst trim on bank 1: the rear oxygen sensor keeps reporting lean exhaust, so the outer loop keeps adding fuel until it reaches its rich limit. GM's Bosch-based 2005 V6 sets it for a correction above +0.03 lambda; GM's 2018 four-cylinders list it as the high limit, with the integral offset at +99 % and total offset at +50 % or more (Type B); Ford's 2020 to 2023 engines set it 5 s after reaching a rear bias trim of +0.087. Air drawn in through an exhaust leak ahead of the rear sensor, a rear sensor skewed lean, or a front sensor reading rich all produce this pattern. Several manufacturers have issued software fixes: GM for the 2013 ATS and Malibu 2.5 (only when long-term trim stays within ±13 %) and for the 2017 Malibu 1.5, Mitsubishi for the 2014 Outlander V6 after a wrong threshold. Subaru's 2025 bulletin corrects the service manual steps for P2096 and P2097 across its range.
- What you may notice
- Malfunction indicator lamp on
- Slightly higher fuel consumption
- Likely causes
- PossibleExhaust leak ahead of the rear oxygen sensor drawing in air
- PossibleRear oxygen sensor skewed lean or aged
- PossibleCalibration issue fixed by an ECM update
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Often possible to do yourself.Typical cost: €0 – €300
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.