Common Checks
- Inspect the oxygen-sensor heater fuse, connector, and wiring.
- Check for harness damage from exhaust heat.
- Confirm heater power and ground before replacing the sensor.
Diagnostic trouble code
P0135 Bank 1 Sensor 1 Oxygen Sensor Heater Circuit
The upstream bank 1 oxygen-sensor heater circuit is not operating as expected.
Oxygen Sensor & Heater CodesCommon Repairs
- Repair melted wiring or poor connector terminals.
- Replace the oxygen sensor if the heater circuit inside the sensor is open.
Mustang Notes
- After header or exhaust work, oxygen-sensor harness routing is a common failure point.
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.