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.
Affected components
- Nh3 sensor heater
- Heater driver
- Sensor wiring
Common causes
- High likelihood: Heater control wire shorted to ground
- Medium likelihood: Internal short across the heater element
- Low likelihood: Low-side driver pulled down in the control module
Diagnostic notes
- The malfunction indicator lamp may illuminate
- This code can affect emissions
Related codes
Sources
Diagnostic information is provided for reference only. Confirm the code with a compatible scan tool and follow the vehicle manufacturer's service procedures before replacing components.