P24E8 NH3 Sensor Heater Circuit High

With P24E8 the heater circuit of the NH3 sensor reads too high. Either the line is shorted to a supply voltage so that the heater cannot be switched off, or the driver measures overcurrent because the element has failed with low resistance. A heater stuck on can overheat and crack the ceramic, so the controller normally shuts it down and stops evaluating ammonia until the fault clears. No manufacturer documents P24E8 publicly. CARB's heavy-duty regulation treats heater current or voltage drop outside the specified limits as a malfunction. Navistar's N13 shows that faults of this heater are reported by the smart sensor itself. P24E7 is the low counterpart, P24E6 the open circuit.

Likely causes

Symptoms

• Malfunction indicator lamp on
• Ammonia sensor reading switched off

Repair estimate

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

Parts involved

Related codes

References: law.cornell.edu, static.nhtsa.gov.