P24E4NH3 Sensor Circuit High
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- How the car detects it
- P24E4 is set when the NH3 sensor signal climbs above anything a working sensor could report, so the value is rejected as electrically impossible rather than merely implausible. Typical reasons are a short to a supply voltage, a broken line pulled up internally, or failing electronics that output a saturated value. In Navistar's layout the ammonia measurement comes from a probe at mid-bed of the SCR catalyst plus a separate control module, so a reading at the upper stop usually points to the link between the two or to that module. No manufacturer publishes thresholds for P24E4. CARB's heavy-duty OBD rule calls for range checks on such sensors. P24E3 is the low fault; the general circuit code is P24E1.
- What you may notice
- Check engine light on
- Ammonia reading pinned at the upper limit
- Possible reduced DEF dosing
- Likely causes
- LikelySignal line shorted to a supply voltage in the harness
- PossibleOpen line between probe and module read as maximum value
- RareSensor electronics module outputting a saturated value
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Usually a job for a workshop.Typical cost: €100 – €1,400
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.