P24E6
NH3 Sensor Heater Circuit/Open
The heater inside the ammonia (NH3) slip sensor warms the sensing cell to operating temperature so it can read tailpipe ammonia. The ECM detects an open in the heater control circuit — no current flows when the heater should be active, so the sensor never reaches its working point and SCR closed-loop control is suspended.
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: medium
Common causes
Ordered by how often each turns out to be the cause.
- Burnt-out heater winding inside the sensorCommon
- Broken wire or unplugged connectorPossible
- Failed heater driver stage in the dosing moduleLess likely
Parts involved
- Nh3 Sensor Heater
- Heater Driver
- Sensor Wiring
P24E6 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.