P0142
O2 Sensor Heater Circuit Malfunction (Bank 1 Sensor 2)
The ECU detects an electrical fault in the heater circuit of the downstream oxygen sensor on bank 1. The heater current is out of range, suggesting an open or shorted heater element, blown fuse or wiring fault.
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: easy
Symptoms
- Check engine light on after several drive cycles
- Slightly increased fuel consumption during cold start
- Delayed entry into closed-loop fuel control
- Failed emissions inspection (lambda readiness)
Common causes
Ordered by how often each turns out to be the cause.
- Sensor heater element openCommon
- Heater fuse blownPossible
- Heater wiring or connector faultPossible
Parts involved
- Oxygen Sensor B1s2
- Oxygen Sensor Heater Fuse
- Oxygen Sensor Heater Wiring
P0142 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.