What does it mean?
P1105 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: O2 Sensor Circuit (Bank 1-Sensor 2) Short to B+ .
Symptoms
- Check engine light on with the catalyst monitor unable to complete
- Readiness monitors staying incomplete, which blocks an emissions test
- Downstream sensor voltage in live data stuck near battery voltage instead of switching
- Slightly increased fuel consumption on vehicles that use the rear sensor for trim correction
- Usually little or no change in how the engine drives, so the fault is found during a scan
- Occasional blown fuse if the short also loads the heater supply
Likely causes
- Chafed sensor harness touching a permanently live wire, often near a heat shield or an underbody clip
- Melted insulation where the sensor loom rests against the exhaust pipe
- Water and corrosion inside the connector bridging the signal pin to the heater supply pin
- Internal short inside the sensor connecting the heater circuit to the signal element
- Incorrect sensor fitted or a connector pinned the wrong way after a previous repair
- Failed module input stage, considered only once the harness and sensor are proven
How to fix it
- Look at the downstream sensor voltage in live data — a value far above the normal switching range confirms the described fault
- Unplug the sensor, switch the ignition on and measure the signal wire against ground; battery voltage with the sensor disconnected proves the short is in the harness
- If the wire is clean, measure between the sensor's heater and signal terminals to find an internal short
- Inspect the loom along the exhaust and underbody for melted, rubbed or crushed insulation and repair it properly
- Check the connector for water, corrosion and terminal tracking; dry, clean and reseal it
- Confirm the correct sensor part and the correct pin arrangement if the vehicle has had recent work
- Repair the harness or fit a new sensor, then verify the signal switches normally and clear the code