Massey Ferguson U 699 (6) – Engine Control Unit (ECU) or SCR Dosing Control Unit (DCU): Inlet line heater power stage error: Shortcut to Ground

This fault code indicates an electrical issue within the Selective Catalytic Reduction (SCR) emissions system. Specifically, the system has detected an "open load" (an open circuit or break in electrical continuity) in the DEF (Diesel Exhaust Fluid / AdBlue) inlet line heater circuit. The control module is sending voltage to the heater but sensing zero current draw, which typically points to a disconnected plug, a broken wire in the harness, or a burnt-out heating element inside the DEF line.

• Massey Ferguson 8600 Series
• MF 8650
• MF 8660
• MF 8670
• MF 8680
• MF 8690
• Sisu Tier 3 engines
• Sisu Tier 4i engines

1. 1

   Inspect the DEF inlet line for physical damage, melting, or severe chafing against the tractor frame that could cause a short to the chassis.

2. 2

   Disconnect the electrical connector for the DEF inlet line heater and inspect the pins for corrosion, water intrusion, or bent terminals.

3. 3

   With the connector unplugged, use a multimeter to check for continuity between the power supply wire on the harness side and a known good ground (indicates a short in the tractor's wiring harness).

4. 4

   Measure the resistance (Ohms) across the heater element pins on the DEF line itself. A reading at or near 0 Ohms indicates the heater element is internally shorted.

1. 1

   Preparation

   Park the tractor on a level surface, turn off the engine, and disconnect the negative (-) battery terminal to prevent electrical spikes during repair.

2. 2

   Access the DEF Lines

   Locate the DEF supply module (pump) and trace the inlet line to the dosing injector. You may need to remove protective guards or panels depending on the exact model.

3. 3

   Relieve Pressure & Drain

   Ensure the DEF system has purged (this usually happens automatically after shutdown). Place a clean catch pan under the connections to catch any residual DEF fluid.

4. 4

   Disconnect Electrical & Fluid Fittings

   Unplug the electrical connector for the inlet line heater. Disconnect the quick-connect fluid fittings at both ends of the DEF inlet line. Note: Cap the open ports on the pump and injector immediately to prevent dirt contamination.

5. 5

   Remove and Replace

   Unclip the faulty DEF inlet line from its routing brackets and remove it from the tractor. Route the new heated DEF line in the exact same path, ensuring it does not rub against sharp edges or hot exhaust components.

6. 6

   Reconnect

   Snap the fluid fittings into place until they click securely. Reconnect the electrical connector for the heater.

7. 7

   Clear Codes

   Reconnect the battery. Use the Massey Ferguson EDT (Electronic Diagnostic Tool) to clear the U 699 (6) fault code from the ECU/DCU. Run the engine and verify that the code does not return.