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

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.

Likely causes

Symptoms

• Malfunction indicator lamp on
• Slightly higher fuel consumption

Repair estimate

Typical range across vehicles; the real cost depends on what the testing finds.

What to check first

1. Check upstream trims
2. Check downstream sensor
3. Look for misfires

Parts involved

Related codes

References: fordservicecontent.com, gsi.ext.gm.com, gsi.ext.gm.com, static.nhtsa.gov.