Case IH 19085 (DTC 857A) - ECU – Engine Control Unit (ECU / ECM): DEF/AdBlue dosing valve ECU driver overtemperature failure

The internal driver circuit within the control module responsible for powering the Diesel Exhaust Fluid (DEF) dosing valve has overheated, likely due to excessive current draw from a short circuit, a failing actuator, or external heat factors.

• MAXXUM T4E
• 240 Series Axial-Flow Combines (7230, 7240, 8240, 9240)
• Magnum (180 through 380)
• Maxxum (115 through 150)
• Puma (140 through 240)
• Optum (270, 300)

1. 1

   Check for Shorts/Wiring Issues: Inspect the wiring harness between the ECU and the DEF dosing valve for a short to ground or a short between the high-side and low-side drivers, which can cause excessive current draw.

2. 2

   Inspect DEF Coolant Lines: Check the DEF tank heater control valve and coolant hoses. Verify the DEF heater line with the 'red' band is installed correctly to prevent continuous hot engine coolant circulation.

3. 3

   Check for Blockages: Verify that the DEF dosing valve and inline filters are not blocked, which can overwork the system. Check the main inline DEF filter and screen.

1. 1

   Verify Coolant Routing

   Ensure the DEF heater line with the 'red' band is correctly connected to the top tube running to the front part of the engine head.

2. 2

   Test the Heater Control Valve

   If the DEF tank is overheating, the heater control valve may be sticking intermittently. If this is the case, replace the heater valve.

3. 3

   Test the Dosing Valve Actuator

   If the wiring is intact and coolant routing is correct, the DEF doser injector itself likely has an internal short causing the ECU driver to overheat.

4. 4

   Replace the Doser Injector/Pump

   Replace the faulty DEF dosing valve/injector or supply module.

5. 5

   Clear Codes

   Use the diagnostic tool to clear the 19085 (857A) fault code and run a dosing test to verify the ECU driver is no longer overheating.