P24E9 is not about a broken wire but about how the heater works: the circuit is intact, yet the NH3 probe does not reach or hold its operating temperature in the expected time, or its temperature control swings. Deutz lists P24E9 for its MD1 engine controller as SPN 4382 with FMI 2, meaning erratic or incorrect heater data. Navistar handles the similar case on the 2013 N13 as SPN 5848 FMI 10, an abnormal rate of change, where the probe or its module are the named suspects. Aged heater elements, cold exhaust from long idling and moisture on the ceramic play a role. CARB's heavy-duty rule requires heater performance checks. Electrical heater faults are P24E6 to P24E8.
Medium severity. Can I keep driving?If the car is running normally, drive in moderation to a repair shop. If it loses power or another warning appears, do not continue.
Symptoms
- Check engine light, often together with an NH3 sensor performance code
- Ammonia reading available late or unstable
Most likely causes
- Aged heater element no longer delivering full power
- Condensate on the ceramic cooling it or causing thermal shock
- Low supply voltage limiting heater power
What to check, in order
Start with the simplest. You can tick off each step.
Good to know
- Repair difficulty: medium
- It affects emissions.
What each character of P24E9 means
- P: Powertrain: engine and transmission
- 2: Generic code: same on every make
- 4: Emissions
- E9: Specific fault in that system
Frequently asked questions
Can I keep driving with code P24E9?
If the car is running normally, drive in moderation to a repair shop. If it loses power or another warning appears, do not continue.
What causes code P24E9?
The most common causes are: aged heater element no longer delivering full power; condensate on the ceramic cooling it or causing thermal shock; low supply voltage limiting heater power.
Related codes
- P24E6NH3 Sensor Heater Circuit/Open
- P24E7NH3 Sensor Heater Circuit Low
- P24E8NH3 Sensor Heater Circuit High
- P24E2NH3 Sensor Circuit Range/Performance
Sources
Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.