P1131 and P1151 OBD Codes After Replacing O2 Sensor on Bank 2 in 1999 Ford F150 V8
After replacing the oxygen sensor on Bank 2 of my 1999 Ford F15-0 V8, I received a new OBD code: P1131 and P1151. Initially, I was given a P174 code after the replacement, but following the repair, the engine exhibited erratic idle behavior and stutters during driving—almost coming to a stop when driving a block away. I inspected the PVC hoses and found no vacuum leaks, yet the issue persists. The current codes are P1131 (O2 sensor upstream Bank 2 signal too lean) and P1151 (which corresponds to P0174 in some scanners—indicating a lean condition in Bank 2). I'm considering replacing the upstream O2 sensor, but I've read that other components such as MAF sensor, fuel pressure, clogged injectors, EGR valve, or even intake system issues could also contribute. The fact that these codes don't always point to a single root cause makes troubleshooting challenging. Does anyone have experience with this specific scenario? Are there known patterns in 1999 F150 V8s where P1131 and P1151 appear after O2 sensor replacement, or could this indicate deeper underlying issues that aren't immediately obvious from the codes alone? Any insights into diagnosing lean conditions or interpreting these codes in real-world driving scenarios would be greatly appreciated.
Check for a lean condition—the engine is likely struggling to maintain proper air-fuel mixture. Potential causes include vacuum leaks, low fuel pressure, restricted fuel injectors, EGR valve malfunction, or MAF sensor issues. These factors can all contribute to a lean reading and trigger P1131 and P1151 codes in the 1999 Ford F150 V8.