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.
Affected components
- Nh3 sensor heater
- Heater driver
- Sensor wiring
Common causes
- High likelihood: Burnt-out heater winding inside the sensor
- Medium likelihood: Broken wire or unplugged connector
- Low likelihood: Failed heater driver stage in the dosing module
Diagnostic notes
- The malfunction indicator lamp may illuminate
- This code can affect emissions
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.