P24EBNH3 Sensor Supply Voltage Circuit Low
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- How the car detects it
- P24EB reports that the power feed of the NH3 sensor module sags below its lower limit. Below that point the heater cannot bring the probe up to temperature and the electronics may reset, so ammonia readings and sensor messages become unreliable. Typical causes are a weak or discharged battery during cranking or long idle, a high-resistance ground strap, corroded fuse contacts or voltage drop along a long chassis harness. No manufacturer documents P24EB publicly; Navistar's N13 material shows the ammonia sensor as a separately powered probe-and-module unit. For heavy-duty engines, CARB wants such circuits checked for undervoltage. P24EA is the general supply fault, P24EC the high one.
- What you may notice
- Warning lamp, often after cold starts
- NH3 sensor drops off the data link at times
- Likely causes
- LikelyWeak or discharged batteries pulling system voltage down
- PossibleHigh resistance in the ground path of the sensor module
- RareCorroded fuse or relay contacts causing voltage drop
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Easy · Often possible to do yourself.Typical cost: €30 – €600
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.