P2099: Post Catalyst Fuel Trim System Too Rich (Bank 2)

P2099 is the bank 2 counterpart of P2097: the rear oxygen sensor of bank 2 keeps reporting lean exhaust, so the post-catalyst trim of that bank adds fuel until it reaches its rich-side limit. Ford sets it 5 s after the bank 2 rear bias trim reaches +0.087, with the closed loop running, coolant between 160 and 250 °F and at least 15 % fuel in the tank; GM's Bosch-based 2005 2.8 and 3.6 V6 and the 2008 3.6 LLT list it as a lean shift of the secondary trim beyond its calibrated limit, over two trips. A typical physical cause is air drawn into the exhaust ahead of the bank 2 rear sensor, at a cracked manifold, a leaking flange or a loose sensor, which makes that sensor read lean. A rear sensor that has aged lean or a front sensor reading rich gives the same result. Check fuel trims and front sensor data of both banks before replacing a sensor.

Medium severity. Can I keep driving?You can usually keep driving, unless you notice a loss of power, which may point to a blockage. The car may not pass an emissions inspection.

Bank 2 is the side without cylinder 1, so it only exists on V or boxer engines.

Symptoms

Malfunction indicator lamp on
Slightly higher fuel consumption

Most likely causes

Exhaust leak ahead of the bank 2 rear sensor
Bank 2 rear oxygen sensor skewed lean or aged

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 P2099 means

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

Frequently asked questions

Can I keep driving with code P2099?

You can usually keep driving, unless you notice a loss of power, which may point to a blockage. The car may not pass an emissions inspection.

What causes code P2099?

The most common causes are: exhaust leak ahead of the bank 2 rear sensor; bank 2 rear oxygen sensor skewed lean or aged.

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.