Case IH 19015 (DTC 4CDE) - ECU – Engine Control Unit (ECU) / Aftertreatment Control Module: NH3 sensor heater control failure

The NH3 (Ammonia) sensor is a critical component of the Selective Catalytic Reduction (SCR) exhaust aftertreatment system. It is used to detect the ammonia concentration in the exhaust gas downstream of the SCR catalyst to ensure the system is dosing Diesel Exhaust Fluid (DEF) correctly. The sensor relies on an internal heater to reach its required operating temperature. This fault code triggers when the system detects an electrical failure, such as an open circuit, short circuit, or abnormal resistance in the sensor's heater control circuit.

• MAXXUM T4E
• Case IH 240 Series Axial-Flow Combines (e.g., 7240, 8240, 9240)
• Case IH Puma Series Tractors (e.g., Puma 220 CVT)
• Case IH Maxxum Series Tractors
• Case IH Farmall Series Tractors (e.g., 110U)
• Case Construction Equipment (e.g., 580N Backhoe Loaders)

1. 1

   Visual Inspection: Inspect the wiring harness connecting the ECU to the NH3 sensor module for chafing, melted wires, or corrosion.

2. 2

   Probe Resistance Test: Disconnect the slide-lock connector separating the NH3 sensor probe from the NH3 sensor module. Using a digital multimeter, measure the trim resistance of the NH3 sensor probe across the heater circuit pins. According to service documentation, the trim resistance must measure between 500 and 2000 ohms. If it falls outside this range, the probe's heater has failed.

3. 3

   Module/Power Check: Verify that the NH3 sensor module is receiving proper 12V supply voltage and ground from the ECU harness.

1. 1

   Disconnect Power

   Disconnect the machine's batteries to prevent arcing, starting with the negative (-) cable.

2. 2

   Locate the Sensor

   Locate the NH3 sensor probe in the middle of the aftertreatment SCR catalyst and the module on the adjacent sensor table.

3. 3

   Disconnect Wiring

   Disconnect the slide-lock electrical connector that links the sensor probe to the module.

4. 4

   Remove the Faulty Component

   If the probe failed the resistance test, carefully unscrew the NH3 sensor probe from the SCR catalyst exhaust pipe. If the module is determined to be faulty, unbolt it from the sensor mounting table.

5. 5

   Install the New Part

   Thread the new NH3 sensor probe into the exhaust pipe and tighten it to the manufacturer's specified torque. (If replacing the module, bolt the new module to the table).

6. 6

   Reconnect

   Reconnect the slide-lock electrical connector.

7. 7

   Restore Power

   Reconnect the battery cables, attaching the negative (-) cable last.

8. 8

   Clear Codes

   Use a diagnostic scan tool to clear the ECU fault codes and run the engine to verify the repair.