Case IH 17685 (F-4365-05) - ECU – Engine Control Module (ECM) or Dosing Control Unit (DCU): DEF/AdBlue quality sensor failure - temperature signal shorted to ground

The control module is receiving a voltage signal from the DEF temperature probe that is below the acceptable threshold, meaning the circuit is shorting directly to ground. This disables the Selective Catalytic Reduction (SCR) dosing system and eventually derates the machine.

• VESTRUM CVX
• Farmall Tractors (40, 45, 50)
• Magnum Series (235-340)
• Steiger Tractors
• Puma Tractors
• Combines
• Compact Track Loaders (SV340B, TR340)

1. 1

   Inspect the wiring harness leading to the DEF tank header/quality sensor for chafing against the frame, melted insulation, or pinched wires that could cause the temperature signal wire to short to the chassis ground.

2. 2

   Disconnect the DEF quality sensor pigtail and inspect the pins for corrosion, bent terminals, or moisture intrusion (DEF fluid is highly corrosive and can wick into connectors).

3. 3

   Using a multimeter, test the temperature signal circuit between the sensor connector and the ECM for continuity to ground. If the harness tests good, the short is internal to the sensor.

4. 4

   Verify that the system battery voltage is within the normal operating range (11V - 32V), as low voltage can cause erratic sensor readings and phantom codes.

1. 1

   Preparation

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

2. 2

   Access the Sensor

   Locate the DEF tank. The DEF quality sensor/header unit is typically mounted on the top of the tank.

3. 3

   Disconnect Lines

   Carefully disconnect the electrical connector and the DEF fluid supply/return lines from the sensor head. Note: Clean up any spilled DEF immediately with warm water, as it is highly corrosive to metal.

4. 4

   Removal

   Remove the mounting bolts or the retaining lock ring securing the DEF header to the tank. Carefully extract the old sensor assembly vertically out of the tank to avoid damaging the float or suction tubes.

5. 5

   Installation

   Insert the new DEF quality sensor assembly. Ensure the O-ring/gasket is properly seated to prevent contamination and leaks. Secure the retaining ring or bolts.

6. 6

   Reconnection

   Reconnect the DEF fluid lines and the electrical connector.

7. 7

   Clear Codes

   Reconnect the battery. Turn the key on and use a diagnostic tool (such as the Case IH Electronic Service Tool or Jaltest) to clear the fault codes and verify that the DEF temperature reading is now registering accurately.