P2097: Post Catalyst Fuel Trim System Too Rich (Bank 1)
The oxygen sensor after the catalytic converter on bank 1 keeps seeing rich exhaust, so the computer has removed as much fuel as it can based on that sensor.
What P2097 means
P2097 is the rich side partner of P2096. The downstream oxygen sensor, which sits after the catalytic converter, keeps reporting rich exhaust, and the computer has used up the correction range it allows for post catalyst fuel trim. That means either the engine is really running rich, the converter is not doing its job, or the downstream sensor is reporting rich when it should not. Leaking injectors, high fuel pressure and an upstream sensor that reads lean when the engine is actually rich can all make the engine run rich. A downstream sensor contaminated by oil or coolant can stick high. A worn converter can also pass rich exhaust through. KBB groups these post catalyst trim codes together and advises not driving long with them. Shops compare upstream and downstream sensor data with fuel trims, check fuel pressure and injector balance, and look for oil or coolant consumption. The goal is to find the source of the rich condition before replacing a sensor or converter.
Common symptoms
- Check engine light on
- Worse fuel economy
- Fuel or rotten egg smell from the exhaust
- Usually no change in driveability
- May appear with P0420 or P0172
Most common causes
- Failing downstream oxygen sensor
- Engine running rich from a leaking injector or high fuel pressure
- Failing catalytic converter
- Contaminated oxygen sensor from oil or coolant burning
- Faulty upstream air-fuel sensor
What to check yourself first
Check whether rich codes such as P0172 are also present. Smell the exhaust for fuel or sulfur. Look for oil burning, such as blue smoke at start up, which can contaminate sensors and converters.
Typical fixes and what they cost
| Fix | Typical cost | Note |
|---|---|---|
| Replace oxygen sensor | $440-$523 | When the downstream sensor reads rich with a normal engine mixture. |
| Fuel pressure test | $60-$88 | Checks for high fuel pressure. |
| Replace fuel injector | $768-$953 | If an injector leaks fuel. |
| Replace catalytic converter | $2,280-$2,480 | Only after the converter is confirmed bad. |
Typical US price ranges for parts and labor, not quotes. Your shop should confirm the cause with a diagnostic before replacing parts.
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Related codes
- P2096 Post Catalyst Fuel Trim System Too Lean (Bank 1)
- P0172 System Too Rich (Bank 1)
- P0420 Catalyst System Efficiency Below Threshold (Bank 1)
- P0138 O2 Sensor Circuit High Voltage (Bank 1 Sensor 2)
- P2271 O2 Sensor Signal Biased/Stuck Rich (Bank 1 Sensor 2)