Powertrain, generic (extended)

P24E1 NH3 Sensor Circuit

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

An NH3 sensor behind the SCR catalyst measures ammonia that slipped through unused, letting the controller trim dosing and detect overdosing or an aged catalyst. P24E1 is the general circuit code for this sensor: its signal is missing, implausible or erratic. Deutz lists P24E1 for its MD1 engine controller with SPN 4377 and FMI 2, i.e. unstable or wrong data. For the 2014 Ram 3500 to 5500 chassis cab with the 6.7 L Cummins, bulletin 18-042-20 offers two calibrations: one for trucks still equipped with the sensor, the other for trucks from which it has been taken off. CARB's heavy-duty rules require SCR sensors to be checked for circuit faults and rationality. Range, low, high and intermittent faults are P24E2 to P24E5; a lost CAN link to the sensor is U02A4.

Likely causes

NH3 sensor element or its electronics failed from heat and age
Heat-damaged wiring or connector near the exhaust
Software calibration issue, update available on some engines

Symptoms

  • Malfunction indicator lamp on
  • Less precise DEF dosing, possible ammonia smell or higher NOx

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€150–900
Time0.5–2 h

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

Parts involved

nh3 sensor

Related codes

P24E2P24E3P24E4P24E5U02A4

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