Oxygen Sensor Stuck Lean - Bank 1, Sensor 2
OBD-II code P2270 represents a fault in the air/fuel sensor circuit that is causing it to run lean in bank 1, sensor 2.
The engine control module, or ECM, monitors the air/fuel ratio of the exhaust using oxygen sensors (more about how oxygen sensors work in this article) -- these sensors are also called air/fuel ratio sensors and o2 sensors. Using the information gathered from these sensors, the ECM tries to keep air/fuel levels at a normal ratio via the fuel system. The oxygen sensor outputs voltage signals that the ECM uses to perform this duty. When the trouble code, P2270 is stored in your Toyota's ECM, the reading is stuck at lean for that sensor and the ECM can no longer accurately regulate the air/fuel ration. The occurrence of the code P2270 will cause a check engine light or SES light to illuminate on your dash.
The majority of the time, the P2270 code initiates from these causes:
- Oxygen sensor malfunction
- Short in the o2 sensor circuit
- Fuel pressure problem or problems with fuel injectors
- Vacuum leaks
- PCV system leaks
- Air/fuel sensor relay faulty
- MAF sensor malfunction
- ECT sensor malfunction
- Fuel leak
As you can see, this problem comes with a long list of possible culprits. Start by checking all of the electrical connections for any loose parts and then do a visual inspection of all wiring and parts. Checking vacuum lines and PCV connections will be the next easiest path for nailing down the problem. If this is the only code your ECM has stored, it's likely a problem with the oxygen sensor or the wiring leading to the o2 sensor. If more than one sensor is throwing a code, or if other system codes exist, the problem will require further diagnostics.
For a comprehensive list of trouble codes, check out this article on the Toyota Parts Center Blog.