P0143: O2 Sensor Circuit Low Voltage Bank 1 Sensor 3

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.

Bank 1 is the side of the engine with cylinder 1. Inline engines only have this bank.

Symptoms

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

Most 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)

What to check, in order

Start with the simplest. You can tick off each step.

1. Check the wiring and connector of the sensor indicated
2. With the connector unplugged, check whether the signal wire is making contact with ground.
3. Look for exhaust leaks
4. Check the signal in live data with the engine warm
5. Check the fuse and the heater resistance if the code mentions it
6. Replace the sensor if it has power and does not respond

Good to know

• Repair difficulty: easy
• It affects emissions.

What each character of P0143 means

• P: Powertrain: engine and transmission
• 0: Generic code: same on every make
• 1: Air and fuel
• 43: Specific fault in that system

Frequently asked questions

Can I keep driving with code P0143?

Yes, you can normally drive in moderation, but get it repaired soon: you will use more fuel and the catalytic converter can be damaged over time.

What causes code P0143?

The most common causes are: 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).

Related codes

• P0144O2 Sensor Circuit High Voltage Bank 1 Sensor 3
• P0142O2 Sensor Circuit Bank 1 Sensor 3
• P0146O2 Sensor Circuit No Activity Detected Bank 1 Sensor 3
• P0137O2 Sensor Circuit Low Voltage Bank 1 Sensor 2
• P0163O2 Sensor Circuit Low Voltage Bank 2 Sensor 3

Sources

• law.cornell.edu: 13 CCR 1968.2
• static.nhtsa.gov: SB 10096822 1020
• static.nhtsa.gov: SB 10105583 9340
• newtonnet.co.uk: fordobd2012

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.