Powertrain, generic (extended)

P24E7 NH3 Sensor Heater Circuit Low

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

P24E7 points to a heater circuit of the NH3 sensor that reads too low: the feedback voltage stays near ground, or the current is far below what the heater should draw. Most often the heater feed is shorted to ground, which can also blow the fuse or switch off the driver to protect it; a heater whose resistance has risen sharply gives a similar picture. The probe then heats slowly or not at all, and the ammonia value stays unavailable. No manufacturer publishes P24E7 with thresholds. CARB's heavy-duty OBD rule demands that heater current or voltage drop outside the maker's limits be flagged. The open-circuit fault is P24E6, the high fault P24E8 and heating performance P24E9.

Likely causes

Heater supply line shorted to ground
Heater element with strongly increased resistance
Blown fuse in the heater supply

Symptoms

  • Check engine light on
  • Ammonia value missing or delayed after start

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€100–1,400
Time0.5–2.5 h

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

Parts involved

nh3 sensor heaterheater driversensor wiring

Related codes

P24E6P24E8P24E9

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