Post Catalyst Fuel Trim System Too Rich Bank 2
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.
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.
Real-world scan data
Figures reflect only diagnostic scans recorded through our own apps and tools. Cars are typically scanned because a symptom or warning light prompted it, so these counts describe our scan records — not the incidence of faults in any model, and not the quality, reliability, or safety of any vehicle. No comparison between manufacturers or models is implied. All trademarks belong to their respective owners; no affiliation or endorsement is implied.
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?+
Can I just clear P2099?+
Related codes
Read & clear P2099 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.