P0143
O2 Sensor Circuit Low Voltage Bank 1 Sensor 3
Oxygen sensor (O2)
Generic OBD-II
Medium
What it means
P0143 means the third oxygen sensor on bank 1 — a downstream sensor used to monitor the catalytic converter — is reporting an abnormally low voltage. It rarely affects how the engine runs, but it will trip the check-engine light and cause an emissions failure. The usual cause is a failed sensor, a signal wire shorted to ground, or a corroded connector.
Medium
Can I keep driving? Yes — this downstream sensor mainly affects emissions monitoring, so the car drives normally, but don't leave it unrepaired.
Common symptoms
What you'll notice
- Check-engine light on
- Failed emissions test
- Slightly reduced fuel economy
- Usually little or no change in how the engine runs
Common causes
Most likely first
- Faulty oxygen sensor at bank 1, sensor 3 (most common)Likely
- Signal wire shorted to ground or damaged wiringCommon
- Corroded or loose connector at the sensorCommon
- Exhaust leak near the sensor skewing its readingLess often
- Faulty ECM (rare)Less often
How to diagnose & fix
Work through it in order
- Read live O2 data to confirm the sensor is reading low or flatlined.
- Inspect the sensor's connector and wiring for a short to ground or corrosion.
- Check for exhaust leaks near the sensor's mounting point.
- Replace the oxygen sensor if wiring and connections are good.
- Consider the ECM only after everything else tests good. Clear and re-test.
FAQ
Quick answers
Is it safe to drive with P0143?+
Yes. This third (downstream) sensor is used for catalyst monitoring, so driveability is normal — but you'll fail an emissions test until it's fixed.
Can I just clear P0143?+
It returns once the ECM sees the low signal again, so the sensor or wiring fault needs to be repaired first.
Related codes
Often seen with P0143
Read & clear P0143 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX