P24E5
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.
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: medium
Common causes
Ordered by how often each turns out to be the cause.
- Corroded or loose sensor connectorCommon
- Chafed or vibrating harness near the exhaustPossible
- Aged ceramic sensor element drifting under heat cyclesPossible
Parts involved
- Nh3 Sensor
- Sensor Wiring
- Sensor Connector
P24E5 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.