I cleaned my MAF sensor, but the P1151 code persists. How can I tell if the oxygen sensor is actually working? Any guidance on troubleshooting this issue would be greatly appreciated.
What???...vacuum leaks? That code means the upstream O2 sensor on Bank 2 is over 10 years old and likely needs replacement!
MMs is correct. Vacuum leaks cause the fuel trim to increase, leading to more fuel being injected to compensate for a lean condition. If the system can't fully correct the imbalance, it may set code P0171 or P0174 instead. Use an O2 sensor scanner to check the actual readings and post back what you observe.
The P1151 code indicates that the upstream O2 sensor on Bank 2 is not properly switching between lean and rich conditions. While there are many potential causes, vacuum leaks are a common factor—especially in older vehicles like a 1998 Ford Mustang. Deteriorated rubber vacuum hoses can create a lean condition. I recommend using an all-data scanner or consulting the official repair manual to follow the diagnostic procedure for this code. Here’s a demo video showing how it works: www.auto-facts.org/autorepairmanuals.html (auto repair manuals available).