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.

Medium severity. Can I keep driving?You can go to a repair shop without extreme urgency, driving in moderation. Do not drag it out: an actually rich mixture overheats the catalytic converter and greatly increases fuel consumption; if you smell gasoline or the car loses power, stop and get it checked.

Bank 1 is the side of the engine with cylinder 1. Inline engines only have this bank.

Symptoms

Malfunction indicator lamp on
Slightly higher fuel consumption

Most likely causes

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

What to check, in order

Start with the simplest. You can tick off each step.

First resolve any misfire or fuel mixture codes
Look for exhaust leaks between the engine and the second sensor
Use live data to compare the signals from both oxygen sensors
Check for a blockage by measuring exhaust back pressure
Replace the catalytic converter only at the end of the diagnosis

Good to know

Repair difficulty: medium
It affects emissions.

What each character of P2097 means

P: Powertrain: engine and transmission
2: Generic code: same on every make
0: Subsystem depends on the code range
97: Specific fault in that system

Frequently asked questions

Can I keep driving with code P2097?

You can go to a repair shop without extreme urgency, driving in moderation. Do not drag it out: an actually rich mixture overheats the catalytic converter and greatly increases fuel consumption; if you smell gasoline or the car loses power, stop and get it checked.

What causes code P2097?

The most common causes are: exhaust leak ahead of the rear oxygen sensor drawing in air; rear oxygen sensor skewed lean or aged; calibration issue fixed by an ECM update.

Related codes

Sources

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.