P24E2NH3 Sensor Circuit Range/Performance
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- P24E2 flags an NH3 sensor whose signal is electrically valid but makes no sense: the ammonia value sticks, drifts or contradicts what the dosing model expects from the SCR catalyst. On heavy trucks the sensor is a smart unit with its own electronics that test probe and circuitry and report over J1939. Navistar lets this self-test run on the 2013 N13 only after the middle of the SCR brick has stayed above 170 °C for five seconds, and lights the MIL after two failed trips. No manufacturer publishes P24E2 with thresholds. CARB's heavy-duty rule obliges makers to check such sensors for rationality. Wiring faults are P24E3/P24E4, dropouts P24E5. The driver sees a warning lamp; DEF dosing becomes less precise.
- What you may notice
- Check engine light after two trips
- DEF consumption noticeably higher or lower than usual
- Possible ammonia smell at the tailpipe
- Likely causes
- LikelySensing element aged or poisoned by deposits, giving a drifting ammonia value
- PossibleUrea crystals around the sensor tip after overdosing
- RareExhaust leak near the sensor diluting the sample
- 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: €250 – €1,400
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.