Post Catalyst Fuel Trim System Too Rich (Bank 2)
The P2099 code means the vehicle's onboard diagnostic system has detected: Post Catalyst Fuel Trim System Too Rich (Bank 2). This is a moderate severity code.
- Keep driving?
- Short distances only
- DIY difficulty
- moderate
- Estimated cost
- $100 - $800 (parts and labor)
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Common Symptoms
- Check Engine Light on
- Engine runs rich on Bank 2
- Black exhaust smoke possible
- Fuel smell from exhaust
- Reduced fuel economy
Probable Causes (Ranked by Likelihood)
- Failed rear oxygen sensor on Bank 2 reading lean falsely Very High
- Internal catalytic converter failure on Bank 2 High
- Fuel injector leaking on Bank 2 Moderate
- Coolant leak into Bank 2 combustion chamber Low
Step-by-Step Diagnostic Procedure
-
Monitor Bank 2 rear O2 sensor switching rate and voltage
-
Check Bank 2 fuel injector balance
-
Inspect Bank 2 catalytic converter for internal failure
-
Check for coolant loss without visible leaks
Common Fixes by Vehicle
What techs usually find when diagnosing P2099 on specific vehicles — tap your vehicle for the fix and the exact part:
2005-2010 Ford F-150/Expedition 5.4L 3V easy DIY
Ford P2099 = Post Catalyst Fuel Trim bank 2 TOO RICH. Usually indicates a failed downstream O2 sensor or a partially failed catalytic converter. Replace the bank 2 downstream O2 first (Motorcraft DY-1182). If P2099 returns, the cat is likely saturated -- check for P0430 alongside.
Labor: 45 min2005-2012 Cadillac CTS/STS 3.6L easy DIY
Cadillac CTS P2099 = post-cat fuel trim rich bank 2. Most commonly a failed bank 2 downstream O2. The sensor reading rich causes the PCM to subtract fuel that doesn't need to be subtracted, throwing the trim out of range. Replace with AC Delco 213-3864 or equivalent OE.
Labor: 45 min2007-2013 Chevy Silverado/Tahoe 5.3L/6.2L easy DIY
GM 5.3L/6.2L P2099 on bank 2 -- replace the downstream O2 sensor with AC Delco. If the catalytic converter is aftermarket, it may not meet OBD-II efficiency requirements and will trigger post-cat trim codes regardless of sensor. CARB-compliant cats are required on these.
Labor: 45 minFrequently Asked Questions
What does P2099 mean?
P2099 indicates the ECM has detected that the post-catalyst fuel trim on Bank 2 is too rich, meaning the system cannot properly adjust fuel delivery based on rear O2 sensor feedback.
Can a bad catalytic converter cause this?
Yes, a failing or internally damaged catalytic converter can cause abnormal rear O2 sensor readings, which triggers post-catalyst fuel trim codes.
Should I replace the oxygen sensor first?
Check for exhaust leaks first, as they are a common and inexpensive cause. Then test the O2 sensor data. Only replace the sensor if testing confirms it is faulty.
Sources
This page is built from documented references. Verify against your own service info before repair work.
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