P2099
Post Catalyst Fuel Trim System Too Rich Bank 2
Fuel & air metering
Generic OBD-II
Medium
What it means
P2099 means the downstream (post-catalyst) oxygen sensor on bank 2 shows the air-fuel mixture running too rich, and the fuel trim system can't correct it. The engine still starts and runs, but a lasting rich condition wastes fuel and can overheat or foul the catalytic converter. Common causes are a skewed rear O2 sensor, a leaking injector or high fuel pressure, or an exhaust leak near the sensor.
Medium
Can I keep driving? The engine starts and drives, but a persistently rich mixture wastes fuel and can foul the catalytic converter — repair it before the cat is damaged.
Common symptoms
What you'll notice
- Check-engine light on
- Reduced fuel economy
- Possible rough running or a rich (fuel) smell from the exhaust
- May fail an emissions test
Common causes
Most likely first
- Skewed or faulty downstream (post-cat) oxygen sensor on bank 2Likely
- A rich-running fault — leaking/dripping fuel injector or high fuel pressureCommon
- MAF or MAP sensor over-reporting airflowCommon
- Exhaust leak near the downstream sensor upsetting readingsLess often
- Aging or contaminated catalytic converterLess often
How to diagnose & fix
Work through it in order
- Scan live fuel trims and upstream/downstream O2 data to confirm the rich condition on bank 2.
- Check fuel pressure and inspect injectors for leaking or poor spray.
- Inspect the downstream O2 sensor and its wiring for faults or contamination.
- Check for exhaust leaks ahead of the rear sensor.
- Correct the underlying rich cause; only consider the converter once fueling is verified.
FAQ
Quick answers
Is it safe to drive with P2099?+
Short-term yes, but running rich for long can overheat and clog the catalytic converter, so fix it soon.
Can I just clear P2099?+
It returns until the rich condition or the downstream sensor issue is corrected.
Related codes
Often seen with P2099
Read & clear P2099 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX