NH3 Sensor Circuit Intermittent/Erratic
The ammonia (NH3) slip sensor downstream of the SCR catalyst delivers an intermittent or erratic signal. The ECM expects a smooth voltage proportional to ammonia concentration in the tailpipe — sudden jumps, dropouts or noise mean the wiring, connector or sensing element is failing. Used to close-loop the AdBlue/DEF dosing strategy.
Affected components
- Nh3 sensor
- Sensor wiring
- Sensor connector
Common causes
- High likelihood: Corroded or loose sensor connector
- Medium likelihood: Chafed or vibrating harness near the exhaust
- Medium likelihood: Aged ceramic sensor element drifting under heat cycles
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.