P24E2 code meaning
NH3 Sensor Circuit Range/Performance
Powertrain system Generic code P24xx codes Check engine light
What P24E2 means
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.
P24E2 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyMedium
- Typical labor0.5 to 2.5 hours
- Clears after repairAfter a drive cycle
Symptoms of P24E2
- Check engine light after two trips
- DEF consumption noticeably higher or lower than usual
- Possible ammonia smell at the tailpipe
Common causes of P24E2
- Most likelySensing element aged or poisoned by deposits, giving a drifting ammonia value
- PossibleUrea crystals around the sensor tip after overdosing
- Less likelyExhaust leak near the sensor diluting the sample
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Nh3 sensor
What each part of P24E2 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 2 | Generic code (second SAE range): it means the same on every make. |
| 4 | Area: auxiliary emission controls (catalytic converter, EGR, EVAP). |
| E2 | The exact fault in that area. |
What to do next
- Note P24E2 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P24E2
What does P24E2 mean?
P24E2 means "NH3 Sensor Circuit Range/Performance". 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. It is a generic code, so it means the same on every make.
Is it safe to drive with P24E2?
Usually yes, for a short time, if the check engine light is steady and the car drives normally. If the light flashes or the car runs badly, stop and have it checked.
Will P24E2 fail an emissions test?
Yes, it can. P24E2 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P24E2 to fix?
Difficulty: medium. A typical repair takes 0.5 to 2.5 hours of work. This is a job for a workshop.
Will P24E2 clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.