P24E9
NH3 Sensor Heater Circuit Performance
The heater of the NH3 slip sensor is electrically intact, but the warm-up profile or steady-state temperature feedback does not match the ECM model. The sensor takes too long to reach operating temperature or drifts away from setpoint, so SCR closed-loop control is delayed or held off.
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: medium
Common causes
Ordered by how often each turns out to be the cause.
- Aged heater with increased resistanceCommon
- Poor thermal contact between heater and sensing cellPossible
Parts involved
- Nh3 Sensor Heater
- Sensor Element
P24E9 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.