What it means
The ECU detects a general electrical fault on the third oxygen sensor in the bank 1 exhaust path (typically located after a second catalyst on diesel or large engines with multi-cat exhausts).
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
Bank 1 Sensor 3 is the third oxygen sensor in the bank 1 exhaust path on vehicles equipped with that sensor. The module monitors its electrical signal circuit, and P0143 sets when it detects a general circuit malfunction rather than a specifically low or high signal.
Common causes
Most likely first.
- Sensor aged or failed
- Sensor wiring open or shorted
Symptoms
- Check engine light on
- Failed emissions test
How to diagnose it
- Use a scan tool to confirm P0143, record freeze-frame data, and check for companion oxygen-sensor or heater codes.
- Verify the vehicle is equipped with Bank 1 Sensor 3 and identify its location from service information.
- Inspect Sensor 3 wiring and connector for exhaust heat damage, corrosion, loose terminals, or a rubbed-through wire.
- Check the sensor's power, ground, heater circuit, and signal path for opens or shorts using the manufacturer's wiring information.
- If the circuit checks out, monitor Sensor 3 data and test the sensor response before deciding whether the sensor itself has failed.
Common fixes
- Repair damaged or shorted Bank 1 Sensor 3 wiring.
- Clean or repair corroded or loose connector terminals.
- Replace a failed Bank 1 Sensor 3 after circuit testing confirms it is faulty.
- Repair a confirmed heater supply or ground fault.
Can I keep driving?
A vehicle that runs normally is usually drivable for a limited period, but the fault can prevent emissions monitoring and cause an inspection failure. If drivability worsens or the engine warning light flashes, stop driving and address the fault promptly.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.