P24E9 NH3 Sensor Heater Circuit Performance

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.

Likely causes

Symptoms

• Check engine light, often together with an NH3 sensor performance code
• Ammonia reading available late or unstable

Repair estimate

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

Related codes

References: serdia.deutz.com, static.nhtsa.gov, law.cornell.edu.