Powertrain, generic (extended)

P24EC NH3 Sensor Supply Voltage Circuit High

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

P24EC is stored when the feed voltage measured at the NH3 sensor module exceeds its upper limit. Overvoltage can damage the heater driver and the electronics, so the module may switch off heating and measurement to protect itself. Likely triggers are a charging system that regulates too high, jump-starting with a higher-voltage source, or a short from a higher feed onto the sensor supply line. No manufacturer publishes P24EC; for the component itself, Navistar's N13 bulletin describes the sensor as a probe paired with its own electronics module on the J1939 link. CARB's heavy-duty rule requires out-of-range detection on such circuits. Check the charging voltage first. P24EB is the low fault, P24EA the general one.

Likely causes

Alternator regulator charging too high
Overvoltage from jump-starting or a booster charger
Sensor supply line shorted to another higher feed

Symptoms

  • Check engine light on
  • Other modules may also report high system voltage

Repair estimate

DifficultyMediumDIY possible
Parts and labour€30–800
Time0.3–2 h

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

Parts involved

nh3 sensorsupply wiring

Related codes

P24EAP24EBP24E4

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