P24E8
NH3 Sensor Heater Circuit High
The heater control circuit of the NH3 slip sensor reads above the expected voltage range. Typically a short to battery voltage or a heater driver stuck high — duty-cycle control is lost, the heater either runs continuously or not at all, and the sensor element risks overheating before the ECM disables it.
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: medium
Common causes
Ordered by how often each turns out to be the cause.
- Heater control wire shorted to battery voltageCommon
- High-side driver stuck onPossible
- Connector pins corroded - high contact resistanceLess likely
Parts involved
- Nh3 Sensor Heater
- Heater Driver
- Sensor Wiring
P24E8 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.