P0143 — O2 Sensor Circuit Low Voltage (Bank 1 Sensor 3)
Can drive — fix at your convenience.
What P0143 means
This code means the rear-most oxygen sensor on Bank 1 (Sensor 3, located after the catalytic converter) is reporting a steadily low voltage, which the computer reads as a constant lean condition or a circuit fault. It's commonly caused by a worn sensor, damaged wiring, a poor connector, or an exhaust leak letting extra air in near the sensor. The repair usually means replacing the oxygen sensor or fixing the related wiring.
Common symptoms
- Check engine light is on
- Slightly worse fuel economy
- Failed emissions or smog test
- No clear change in how the car drives
- Possible faint exhaust odor
Common causes
- Worn or contaminated rear oxygen sensor
- Exhaust leak near the sensor letting air in
- Damaged wiring or short to ground
- Loose or corroded connector
- An actual lean running condition
Typical repair cost
$150 – $400
Varies by vehicle and root cause.
Frequently asked questions
Can I keep driving with a P0143 code?
Usually yes, in the short term. This rear sensor is for emissions monitoring rather than engine control, so the car should drive normally. Get it checked within a week or two, and expect the car to fail an emissions test until it's fixed.
How much does it cost to fix a P0143 code?
Most repairs cost between $150 and $400. The oxygen sensor is the main expense, with labor depending on how accessible it is. A wiring or connector repair instead of a sensor can come in lower.
Is a P0143 code serious?
No, it's a low-severity code. The engine isn't in danger and you can drive short term, but it affects emissions monitoring and can slightly reduce fuel economy. Fixing it promptly avoids a failed inspection and keeps it from hiding a related fault.
What does Sensor 3 mean in P0143?
Sensor 3 is the rear-most oxygen sensor on that bank, found on vehicles with extra sensors after the catalytic converter. Like Sensor 2, it mainly watches converter and emissions performance rather than directly tuning the engine. A low-voltage reading here usually points to the sensor itself or an exhaust leak nearby.