P2271
O2 Sensor Signal Biased/Stuck Rich Bank 1 Sensor 2
The engine computer sees the rear oxygen sensor on bank 1 reporting rich exhaust conditions when it should vary normally. This can be caused by a bad sensor, wiring issue, exhaust leak, or an engine problem affecting fuel mixture.
- SEV
- 3/5
- DRIVE
- CAUTION
- DIY
- $20-$150
- SHOP
- $120-$500
Quick answer
What it means
Can you drive with it?
Most common causes
- Faulty Bank 1 Sensor 2 oxygen sensor
- Damaged, corroded, or loose sensor wiring or connector
- Exhaust leak or exhaust contamination affecting sensor readings
Typical repair cost
DIY usually runs $20-$150. Typical shop repair lands around $120-$500, depending on the root cause.
01 / Definition
P2271 indicates the powertrain control module has detected that the Bank 1 Sensor 2 oxygen sensor signal is biased rich or stuck indicating rich exhaust conditions. This is the downstream sensor located after the catalytic converter, so the code often points to sensor performance, wiring faults, exhaust contamination, or less commonly an engine/fuel control issue affecting exhaust composition.
02 / Drive status
With caution. The vehicle may still be drivable, but fuel economy, emissions, and catalyst protection can be affected. If the engine runs poorly, smells strongly of fuel, or the check engine light is flashing, stop driving and diagnose it sooner.
03 / Symptoms
- Check engine light on
- Reduced fuel economy
- Possible failed emissions test
- Fuel smell or rough running if a rich engine condition is present
04 / Causes
| 1 | Faulty Bank 1 Sensor 2 oxygen sensor | high |
|---|---|---|
| 2 | Damaged, corroded, or loose sensor wiring or connector | high |
| 3 | Exhaust leak or exhaust contamination affecting sensor readings | medium |
| 4 | Rich-running engine condition from fuel control or injector issues | medium |
| 5 | Failed or inefficient catalytic converter | low |
| 6 | PCM software or driver circuit issue | low |
05 / Diagnostic sequence
- 01Check for additional codes, especially fuel trim, misfire, O2 sensor, or catalyst-related codes.
- 02Inspect the Bank 1 Sensor 2 wiring, connector, and exhaust area for heat damage, corrosion, oil, or contamination.
- 03Review live data to see whether the downstream O2 sensor is fixed rich, slow to respond, or compared against upstream sensor behavior.
- 04Check for exhaust leaks and verify the engine is not running excessively rich due to fuel trim, injector, or pressure problems.
- 05If wiring and engine mixture are normal, test or substitute the Bank 1 Sensor 2 sensor before considering catalyst or PCM issues.
06 / Repairs
| 1 | Repair damaged wiring, clean corroded connectors, or fix exhaust leaks near the sensor | $20-$200 |
|---|---|---|
| 2 | Replace the Bank 1 Sensor 2 oxygen sensor if testing confirms it is biased or stuck rich | $50-$200 |
| 3 | Correct engine rich-running causes such as leaking injectors, faulty fuel pressure regulation, or bad sensors affecting mixture | $50-$500 |
| 4 | Replace the catalytic converter only if testing shows it is contaminated, inefficient, or causing false sensor behavior | $300-$1,500 |
07 / Related codes
08 / FAQ
Is P2271 always a bad oxygen sensor?
No. A faulty sensor is common, but wiring damage, exhaust leaks, rich fuel mixture problems, and catalyst issues can also trigger it.
Is Bank 1 Sensor 2 the upstream or downstream sensor?
It is the downstream sensor, located after the catalytic converter on bank 1.
Will clearing the code fix the problem?
Clearing the code may turn the light off briefly, but the code usually returns if the underlying fault is still present.
09 / Source and method
- DATA BASIS
- OBD-II REFERENCE + OBD2.HELP
- METHOD
- STATIC VALIDATION
- SAFETY
- INFORMATIONAL
This page combines OBD-II diagnostic reference data with OBD2.help generated diagnostic guidance for code meaning, likely causes, and repair direction.
Publishing uses deterministic schema and build validation, plus manual spot checks on representative pages before release.
Safety-critical diagnosis and repairs should be confirmed with a qualified mechanic, especially when the vehicle is misfiring, overheating, or losing power.