P24E7
NH3 Sensor Heater Circuit Low
The heater control circuit of the ammonia (NH3) slip sensor reads below the expected voltage range. Either the wiring is shorted to ground or the heater driver in the SCR/dosing module is stuck low. The sensor element never warms up, NH3 readings stay invalid and the SCR strategy falls back to open-loop dosing.
- 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 groundCommon
- Internal short across the heater elementPossible
- Low-side driver pulled down in the control moduleLess likely
Parts involved
- Nh3 Sensor Heater
- Heater Driver
- Sensor Wiring
P24E7 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.