1998 Mustang 3.8L P1151 Fault: Diagnosis and O2 Sensor Replacement Guide

The P1151 code typically points to low voltage (lean) readings from the B2S1 oxygen sensor. Using an OBD2 scanner, what is the actual voltage output of this sensor? You can perform a carburetor cleaner test by spraying it into the intake manifold — if the engine responds with a richer condition, it suggests the sensor may be faulty or misreading. Additionally, verify fuel pressure and inspect for any vacuum leaks at the intake system.

I sprayed carb cleaner over the entire top of the engine, focusing on all vacuum lines and hoses. The idle remained stable with no noticeable change — this suggests there's likely no significant vacuum leak. I'm now planning to check the B2S1 sensor voltage using my OBD2 scanner later today.

To test the oxygen sensor: spray carb cleaner into the throttle body (TB) to see if the engine responds with a richer condition — this would indicate the sensor is reacting properly. Are there any other diagnostic codes present? Could an intake manifold gasket leak be contributing to the lean reading?

No additional fault codes are currently stored in the system. I've already tested for vacuum leaks and found none. I'll perform the carb cleaner test on the intake now — no noticeable change was observed during my previous attempt.

I connected my OBD2 scanner to the vehicle. The B2S1 sensor is not switching properly, while B2S2 shows steady voltage around .700 with minimal fluctuation — indicating a lean condition. Bank one upstream (B1S1) and bank two upstream (B2S2) are functioning normally. However, the downstream B2S2 sensor fails to switch at all. I'm going to replace the B2S2 sensor as it appears to be the root cause of the P1151 code.

What is the actual voltage reading from the B2S1 oxygen sensor? This will help confirm whether the issue lies with that specific sensor or another component in the system.

Specifically, I'm looking at the B2S1 voltage. The readings were consistent with B1S1 and showed normal switching behavior — this led me to suspect a failure in the B2S2 sensor. All other systems are nominal: no vacuum leaks, no intake plenum issues, stable fuel pressure, and no leaking injectors. I've confirmed there's no exhaust leak before or after the catalytic converter. I'm now pulling the B2S2 sensor for replacement — it was not switching at all, which confirms the diagnosis.