P1148 indicates that the Powertrain Control Module (PCM) has detected a problem with the closed‑loop fuel control function on bank 1. The PCM has entered open‑loop mode because it cannot verify that the oxygen sensor feedback is being used correctly.
A faulty or intermittent Bank 1 oxygen sensor, wiring, or connector can prevent the PCM from receiving accurate feedback, triggering the code.
Air entering the exhaust before the sensor skews the sensor reading, causing the PCM to think the closed‑loop control is malfunctioning.
A malfunctioning injector or extreme fuel trim error can cause the PCM to lose closed‑loop control.
High resistance or intermittent connection can disrupt the sensor signal, leading to the code.
Only after ruling out sensor, wiring, and exhaust issues should a PCM malfunction be considered, as it is an uncommon cause.
Replacing the PCM is rarely needed. Most cases are caused by a sensor, wiring, or exhaust leak. Only replace the PCM after all other possibilities have been eliminated and the problem persists.
A failing fuel pump can affect overall fuel delivery but does not directly trigger the closed‑loop control code. The code is specific to the feedback loop from the Bank 1 oxygen sensor.
Yes. The PCM will set the code again if the underlying condition (sensor, wiring, or exhaust issue) remains unresolved.
Not directly. The code monitors the oxygen sensor’s ability to control fuel trim, not the converter’s efficiency. However, a severely damaged converter can cause exhaust leaks that affect sensor readings.