Common Checks
- Inspect for exhaust leaks ahead of the upstream sensor.
- Check the sensor connector and harness near the exhaust.
- Review fuel trims and misfire data because mixture faults can make an oxygen sensor look slow.
Diagnostic trouble code
P0133 Bank 1 Sensor 1 Oxygen Sensor Slow Response
The upstream oxygen sensor on bank 1 is switching more slowly than expected.
Oxygen Sensor & Heater CodesCommon Repairs
- Repair exhaust leaks or wiring damage.
- Replace the upstream oxygen sensor if the circuit and mixture checks pass.
Mustang Notes
- Bank 1 is the passenger side on traditional Ford V-engines.
Model-Year Applicability
Listed for 1996 and newer traditional gasoline Mustang pages in this first-pass catalog. Engine, calibration, and Ford-specific codes may narrow that range as more service data is added.