OBD-II Error Code P0143: How to Fix It (O2 Sensor Low Voltage B1S3)

Q: Can I drive with P0143?

In most cases, yes. P0143 is a downstream sensor that primarily monitors catalytic converter efficiency. The engine should run normally, but fuel economy may drop slightly. However, it's best to fix it to pass emissions tests.

Q: Is Bank 1 Sensor 3 the same on all cars?

Bank 1 refers to the side of the engine with cylinder #1. Sensor 3 is the second downstream sensor (after the catalytic converter), so it's the third sensor from the engine on that bank. Check your vehicle repair manual.

Q: Will P0143 cause a failed emissions test?

Yes, because the check engine light will be on, which typically causes an automatic failure in many areas.

Q: Can a bad catalytic converter cause P0143?

A failing catalytic converter can cause the downstream O2 sensor to read low voltage, but the code is for the sensor itself. Diagnose the sensor first, then check converter function if the code returns.

Q: Do I need to replace all O2 sensors at once?

No. Only replace the faulty sensor. However, if others are old, consider replacing them preventively.

Abstract

Error P0143 indicates that the oxygen sensor in Bank 1, Sensor 3 (downstream) is reporting a voltage lower than expected. This typically means the sensor signal is weak or missing, often due to a faulty sensor, wiring issues, or exhaust leaks. Follow these steps to diagnose and fix the problem.