P0143
O2 Sensor Circuit Malfunction (Bank 1 Sensor 3)
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).
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: easy
Symptoms
- Check engine light on
- Increased fuel consumption
- Possible rough idle or hesitation
- Failed emissions test
Common causes
Ordered by how often each turns out to be the cause.
- Sensor aged or failedCommon
- Sensor wiring open or shortedPossible
Parts involved
- Oxygen Sensor B1s3
- Oxygen Sensor Wiring
P0143 is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.