For some time, my Pontiac G8 GT was running on regular grade gas. On a whim, and with gas prices down, I decided to fill up with premium fuel before a road trip. Prior to this, the check engine light (CEL) was a frequent visitor, illuminating shortly after each reset. However, after switching to premium, the CEL stayed off, and remained off for several tanks of gas and around 500 miles. This led me to suspect that the cheaper regular gas might have been contributing to the issue. But, inevitably, the light returned, signaling it was time for a deeper dive.
Initially suspecting the catalytic converter, given common discussions around the P2271 code, I ordered a replacement part as a preemptive measure from Rock Auto. The fault code P2271 specifically points to a “Bank 1 Sensor 2 Oxygen Sensor Signal Stuck Rich,” often abbreviated to B1 S2. This sensor, located downstream of the catalytic converter on Bank 1, is crucial for monitoring the converter’s efficiency. If it signals a consistently rich mixture, it can indicate a problem with the catalytic converter itself, or potentially the sensor.
Upon receiving the new catalytic converter, I decided to dismantle the exhaust system to inspect the existing one. This is what I found:
As you can see from the images, the catalytic converter appeared to be in good condition. There was no visible damage to the monolith, and no blockage that I could detect. Despite initial suspicions, the catalytic converter didn’t seem to be the culprit for the P2271 code and the B1 S2 sensor reading.
While I had the system disassembled, I opted to replace the downstream O2 sensor, the B1 S2 sensor, on that side of the exhaust. It’s a relatively accessible component when the catalytic converter is removed, and given the fault code, it seemed like a logical step. Accessing the upstream sensor, or B1 S1 sensor, looked like a task for another day.
Interestingly, during the process of removing the catalytic converter, I disconnected the battery ground cable. Upon reassembly, I noticed the ground cable nut was loose. A loose ground can cause a myriad of electrical issues in a vehicle, and while a ground problem hadn’t initially occurred to me, the consistent P2271 code could potentially be related to unstable sensor readings due to poor grounding.
After reassembling everything, including tightening the ground cable and installing a new B1 S2 oxygen sensor, I took the car for a test drive. Leaving the battery disconnected for about an hour during the repair had cleared the CEL. During the drive, the CEL remained off, and the car subjectively felt smoother. The only change made that afternoon was the replacement of the pre-catalyst O2 sensor and ensuring a secure ground connection.
Moving forward, the next few days will be crucial to observe if the CEL returns. While the catalytic converter itself seemed fine, the combination of a new B1 S2 sensor and a tightened ground connection might have addressed the underlying issue causing the P2271 code. Further monitoring is needed to definitively pinpoint the root cause and ensure a lasting solution.
