Massey Ferguson U 441 - U 442 - U 697 – Engine Control Unit (ECU) / Dosing Control Unit (DCU): SCR / AdBlue Emissions System Electrical or Plausibility Malfunctions

U 441 indicates a catalyst downstream (post-catalyst) temperature sensor error. U 442 indicates a catalyst upstream (pre-catalyst) temperature sensor error. U 697 indicates a back flow line heater power stage error.

• 8600 Series
• 8650
• 8660
• 8670
• 8680
• 8690
• 6600 Series
• 7600 Series
• 7700 Series
• 8700 Series

1. 1

   Identify the specific FMI sub-code using a diagnostic tool (e.g., FMI 3 or 4 indicates a wiring short, while FMI 16 or 18 indicates a plausibility issue).

2. 2

   Inspect the wiring harness leading to the SCR catalyst for melted wires, chafing, or corrosion in the connectors for both upstream and downstream temperature sensors.

3. 3

   For U 697, disconnect the AdBlue back flow line heater and use a multimeter to check for continuity, proper resistance, and open load (FMI 5).

4. 4

   Check the AdBlue filter maintenance schedule, as a clogged filter can cause system pressure and temperature irregularities.

1. 1

   Cool Down

   Park the tractor on level ground, turn off the engine, and allow the exhaust and SCR catalyst system to cool completely to prevent severe burns.

2. 2

   Disconnect Power

   Disconnect the negative battery terminal to prevent electrical spikes while working on the ECU/DCU sensor circuits.

3. 3

   Locate the Faulty Component

   For U 442, locate the temperature sensor threaded into the exhaust pipe before the SCR catalyst. For U 441, locate the sensor threaded into the exhaust pipe after the SCR catalyst. For U 697, trace the AdBlue return line (back flow line) from the dosing module to the tank to locate the faulty heated hose section.

4. 4

   Remove the Sensor/Line

   Disconnect the electrical pigtail. Use an appropriate wrench or O2 sensor socket to carefully unthread the temperature sensor from the exhaust bung. If repairing U 697, disconnect the DEF line fittings and remove the heated hose assembly.

5. 5

   Install the New Part

   Apply a small amount of high-temp anti-seize to the threads of the new temperature sensor (avoiding the sensor tip). Thread it in by hand to prevent cross-threading, then torque to OEM specifications.

6. 6

   Reconnect

   Reconnect the sensor or heater electrical connectors, ensuring the weather seals are intact and the plug clicks securely. Reconnect the battery.

7. 7

   System Reset

   Connect an AGCO EDT (Electronic Diagnostic Tool) or a compatible scanner (like Jaltest). Clear the inactive fault codes. You must perform a 'Temperature sensor reset' and an inducement counter reset in the software to bring the tractor out of any power derate/limp mode.