P0143O2 Sensor Circuit Low Voltage Bank 1 Sensor 3
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- Sensor 3 is a third oxygen sensor on bank 1, behind a second converter or converter brick. It only exists on some vehicles – documented for Jaguar Land Rover's 3.0 V6 supercharged (2013–2016, where sensor 2 is 'mid-cat' and sensor 3 'post-cat') and Ford systems that monitor part of the converter volume. P0143 means the signal of sensor 3 stays below its lower limit – typically a short to ground, or on some systems an open circuit. Jaguar Land Rover assigns it to the post-cat sensor; Ford applies the same pull-up resistance check as for sensor 2 (open above 1 MΩ, short below 10 Ω). Code-specific thresholds for sensor 3 are not published. When it fails, the control module stops the downstream trim and cannot evaluate the converter; there is no limp mode.
- What you may notice
- Check engine light on (usually after two drive cycles)
- Catalyst monitor readiness not set
- Usually no noticeable change in driving
- Likely causes
- LikelySignal wire shorted to ground or melted against the exhaust
- LikelySensor faulty (cracked element, thermal shock from water)
- PossibleSignal circuit open (counts as low on Ford)
- PossibleExhaust leak ahead of the sensor (lean reading)
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Easy · Often possible to do yourself.Typical cost: €60 – €250
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.