Fuel & air metering · Powertrain · generic (SAE-defined)
P2099: Post Catalyst Fuel Trim System Too Rich (Bank 2)
P2099 means the bank 2 downstream oxygen sensor reports rich exhaust after the catalytic converter, and the computer cannot lean the mixture enough to correct it.
Standard title per SAE J2012 / ISO 15031-6 · Updated 2026-11-07 · By CarWhere Research
How P2099 sets
The powertrain control module (PCM) applies a post-catalyst fuel trim based on the bank 2 sensor 2 oxygen sensor. If the trim reaches its maximum fuel reduction while the sensor still indicates rich, P2099 is stored. The exact limits vary by manufacturer.
Common causes of P2099
Roughly most likely first; the actual cause depends on the vehicle and needs testing to confirm.
- Faulty bank 2 sensor 2 oxygen sensor
- Bank 2 upstream air-fuel sensor skewed
- Leaking fuel injector on bank 2
- High fuel pressure
- Degraded bank 2 catalytic converter
- Oil burning on bank 2 cylinders
P2099 symptoms
- Check engine light on
- Lower fuel economy
- Possible rotten-egg or fuel smell
- Usually no obvious drivability issue
How P2099 is diagnosed
- Read all codes and freeze frame; look for P0175 or bank 2 sensor codes.
- Compare bank 1 and bank 2 fuel trims and sensor activity.
- Verify the bank 2 sensor 2 responds to a forced rich and lean change.
- Test fuel pressure and check for leaking injectors on bank 2.
- Check for oil consumption or contaminated spark plugs on bank 2.
- Assess catalytic converter condition.
Typical fixes for P2099
- Replace the bank 2 sensor 2 oxygen sensor
- Replace the bank 2 upstream air-fuel sensor
- Repair a leaking injector or fuel pressure fault
- Address oil consumption on bank 2
- Replace the bank 2 catalytic converter if failed
Replace parts only after testing confirms the cause — a code names the circuit or condition that failed a check, not necessarily the faulty part. We don’t publish per-repair prices; for what households actually spend on upkeep, see car repair costs.
Related codes & warning lights
P2099 FAQ
What does code P2099 mean?
P2099 means the bank 2 downstream oxygen sensor reports rich exhaust after the catalytic converter, and the computer cannot lean the mixture enough to correct it. The standard definition is "Post Catalyst Fuel Trim System Too Rich (Bank 2)."
Can I drive with a P2099 code?
You can usually drive it for now, but get it diagnosed within days. A rich condition on bank 2 raises fuel use and can harm that side's catalytic converter.
Why would only bank 2 run rich?
A bank-specific problem, such as a leaking injector or a skewed sensor on that side, affects only one bank; shared problems like fuel pressure usually show on both.
Can replacing the downstream sensor alone fix P2099?
It can if that sensor is faulty, but confirm with live data first, since a rich-running engine will make a new sensor read rich too.
Keep researching
Engine guides by brand (known issues, specs)
More fuel & air metering codes
Sources
- SAE J2012 — Diagnostic Trouble Code Definitions (standard code titles)
- ISO 15031-6 — Road vehicles: communication between vehicle and external equipment for emissions-related diagnostics, Part 6: Diagnostic trouble code definitions
- U.S. EPA — Vehicle Emissions Inspection and Maintenance (I/M) programs
- U.S. EPA, 40 CFR 86.1806-17 — Federal onboard diagnostics requirements for light-duty vehicles
- California Air Resources Board — On-Board Diagnostic (OBD) Program
General information written by CarWhere Research, not a diagnosis of your vehicle. Manufacturers can add their own sub-definitions and test conditions; confirm with the factory service information for your year, make and model. Before paying for a repair, check NHTSA for open recalls and your warranty booklet: federal law requires an emissions warranty on major emission-control parts such as the catalytic converter and engine computer.