P2097: Post Catalyst Fuel Trim System Too Rich (Bank 1)

What does P2097 mean?

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.

The code tells you which monitor failed, not which part is broken. Test before replacing parts.

Symptoms

• Malfunction indicator lamp on
• Slightly higher fuel consumption

Common causes

• Medium Exhaust leak ahead of the rear oxygen sensor drawing in air
• Medium Rear oxygen sensor skewed lean or aged
• Medium Calibration issue fixed by an ECM update

Likelihood is a general estimate across vehicles; your make and model may differ.