Powertrain, generic · Fuel and air metering

P0143 O2 Sensor Circuit Low Voltage Bank 1 Sensor 3

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

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.

Likely causes

Signal wire shorted to ground or melted against the exhaust
Sensor faulty (cracked element, thermal shock from water)
Signal circuit open (counts as low on Ford)
Exhaust leak ahead of the sensor (lean reading)

Symptoms

  • Check engine light on (usually after two drive cycles)
  • Catalyst monitor readiness not set
  • Usually no noticeable change in driving

Repair estimate

DifficultyEasyDIY possible
Parts and labour€60–250
Time0.2–1 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

oxygen sensor bank1 sensor3oxygen sensor wiringcatalytic converter

Related codes

P0144P0142P0146P0137P0163

References: law.cornell.edu, static.nhtsa.gov, static.nhtsa.gov, newtonnet.co.uk.