Case IH 19742 – DCU (Dosing Control Unit): Main Relay opens too early / too late (19742) / Too high UREA Temperature in Pump module (19748)

For 19748 (P2043): The system has detected that the temperature of the Diesel Exhaust Fluid (DEF / Urea) inside the pump module is excessively high, or the internal temperature sensor is reading out of its allowable range, triggering an emergency shut-off. For 19742 (P0685): The main power relay to the engine/dosing controller is opening too early before the system can save its data (EEPROM update), indicating a circuit interruption.

• Tier 4a
• Magnum series (180–370)
• Steiger series (350–600)
• Puma series (130–215)
• Maxxum series (110–145)
• Axial-Flow series (5130–9230, 5140–9240, 7250, 8250)
• Patriot series (2250, 3240, 3340, 4430)
• Trident 5550

1. 1

   Compare the urea tank temperature to the pump module temperature. If the tank is below 50°C (122°F) but the pump is overheating, the issue is isolated to the pump module or its heating circuit.

2. 2

   Inspect the DEF tube heating circuit to ensure it is properly switching off. Look for a short circuit to the battery on the heating wire that could artificially overheat the fluid.

3. 3

   Inspect the wiring harness and connectors connecting to the DEF pump module for corroded pins, chafed wires, or loose connections causing an out-of-range reading.

4. 4

   Test the ECM/PCM main power relay and its control circuit for open loops or shorts (if addressing the specific 19742 relay code).

1. 1

   Preparation

   Turn off the machine, remove the key, and disconnect the battery to prevent electrical shorts.

2. 2

   Locate the Pump

   Locate the DEF pump module (Denoxtronic supply module), typically mounted on a bracket near the DEF tank.

3. 3

   Disconnect Lines

   Carefully disconnect the DEF inlet, outlet, and backflow lines. Note: DEF fluid can crystallize and be corrosive; clean any spills with warm water immediately.

4. 4

   Disconnect Electrical

   Unplug the main electrical harness connector from the pump module.

5. 5

   Remove the Module

   Unbolt the pump module from its mounting bracket and remove it from the machine.

6. 6

   Install the New Module

   Mount the replacement DEF pump module, reconnect the fluid lines securely, and plug in the electrical connector.

7. 7

   Programming

   A new DEF pump module must be programmed and calibrated to the vehicle's DCU using the Case IH Electronic Service Tool (EST) laptop software.

8. 8

   Testing

   Clear the fault codes, cycle the key, and run a system test to ensure the DEF system primes successfully without leakage or temperature errors.