Case IH 17675 (F-3364-18) - ECU – Engine Control Module (ECM) / Engine ECU: DEF/AdBlue quality sensor detects concentration is too low with time based evaluation.

The DEF quality sensor has detected that the urea concentration in the DEF tank has fallen outside the acceptable range (which should be 32.5% urea). This code is typically triggered when the DEF has been diluted with water, has degraded due to age or extreme heat exposure, or if the DEF quality sensor itself has drifted or failed.

• VESTRUM CVX
• Magnum series (235-340)
• Optum series
• Puma (115 onwards)
• Maxxum (115 onwards)
• Farmall series (40-45-50 CVT)
• Austoft 9900 sugarcane harvesters

1. 1

   Test the DEF fluid in the tank using a DEF refractometer to ensure it measures exactly 32.5% urea concentration (diagnosing diluted or degraded fluid).

2. 2

   Visually inspect the DEF quality sensor (located in the DEF header unit) and its wiring harness for chewed wires, corrosion, or ammonia gas leaking into the circuit board.

3. 3

   Test the sensor's resistance (typically 300-600 kΩ at room temperature) and perform a wiggle test on the wiring and connectors to check for intermittent voltage drops or shorts.

4. 4

   Check for underlying low battery voltage codes (e.g., SPN 168, FMI 1) to rule out a dying battery or failing alternator causing CAN bus dropouts.

1. 1

   Drain and Flush

   If the refractometer shows the DEF is diluted or degraded, drain the DEF tank completely. Flush the system and refill it with fresh, API-certified DEF fluid. Clear the codes and run the machine to see if the fault returns.

2. 2

   Access the DEF Header

   If the fluid is good but the code persists, the DEF quality sensor has likely failed (sensor drift). Locate the DEF header unit on the top of the DEF tank.

3. 3

   Replace the Sensor/Header

   Disconnect the electrical harness and the DEF dosing lines from the header. Unbolt the flange assembly and remove the DEF header unit from the tank. Install the new DEF quality sensor/header assembly.

4. 4

   Reassemble and Clear Codes

   Reconnect the fluid lines and electrical connectors. Use a diagnostic scan tool to clear the fault codes and perform a system test or forced regeneration to verify the SCR system is reading the correct urea concentration.