Case IH 17686 (F-4365-31) - ECU – Engine Control Unit (ECU): DEF/AdBlue quality sensor failure - temperature signal measurement error

This fault code indicates an internal failure or circuit issue within the Diesel Exhaust Fluid (DEF) quality sensor, specifically relating to the temperature measurement signal. The system has detected that the temperature signal is either shorted to ground, shorted to the battery, or providing an implausible reading outside of the valid measurement range.

• VESTRUM CVX
• Magnum
• Steiger
• Puma
• Optum
• Maxxum
• Austoft 9900
• WD1504

1. 1

   Inspect the wiring harness leading to the DEF tank header/quality sensor for chafing, melted wires, or pinched sections that could cause a short to ground or battery.

2. 2

   Disconnect the DEF quality sensor connector at the DEF tank and inspect the pins for corrosion, moisture intrusion (DEF crystallization), or pushed-back pins.

3. 3

   Use a multimeter to check for continuity and verify that the temperature signal wire is not shorted to the ground wire or the power supply wire within the chassis harness.

4. 4

   Inspect the DEF fluid to ensure the tank is free of debris, as heavily degraded or contaminated DEF can sometimes cause internal sensor scaling or failure.

1. 1

   Prep the Machine

   Park the machine on a level surface, turn off the engine, and disconnect the battery.

2. 2

   Drain the DEF Tank

   Drain the DEF fluid into a clean container until the fluid level is below the header mounting hole to prevent spills.

3. 3

   Disconnect Lines

   Carefully disconnect the electrical connector, the DEF suction/return lines, and the engine coolant lines (which run through the header to thaw frozen DEF) from the top of the DEF header. Note: Clamp the coolant lines to prevent coolant loss.

4. 4

   Remove the Header

   Unscrew the locking ring or remove the mounting bolts securing the DEF header to the top of the DEF tank.

5. 5

   Extract the Unit

   Carefully pull the old DEF header/quality sensor assembly straight up and out of the tank.

6. 6

   Install the New Unit

   Insert the new DEF header assembly, ensuring the rubber mounting gasket/O-ring is properly seated to prevent leaks. Tighten the locking ring/bolts to OEM torque specs.

7. 7

   Reconnect

   Reattach the coolant lines, DEF fluid lines, and the electrical connector.

8. 8

   Refill and Clear Codes

   Refill the tank with fresh, high-quality DEF. Reconnect the battery and use a diagnostic tool (such as the CNH Electronic Service Tool or Jaltest) to clear the inactive fault codes and reset the SCR system parameters.