Massey Ferguson U 699 – Engine Control Unit (ECU): Inlet line heater power stage error

This system preheats the intake air to aid in cold weather starting. The code typically presents with one of three Failure Mode Identifiers (FMI) indicating an electrical circuit malfunction: U 699 3 (Shortcut to Battery +), U 699 5 (Open load), or U 699 6 (Shortcut to Ground).

• 8600 Series
• 8650
• 8660
• 8670
• 8680
• 8690

1. 1

   Inspect the wiring harness leading to the inlet line heater for chafing, melted insulation, or pinched wires that could cause a short to ground (FMI 6) or a short to battery (FMI 3).

2. 2

   Isolate the component by disconnecting the wire directly at the intake heater. If the short circuit error still exists with the heater unplugged, the fault lies within the wiring harness or the control module itself. If the error changes or clears, the heater element is internally shorted.

3. 3

   Test the heater element using a multimeter for continuity and resistance. An infinite resistance reading confirms an 'Open load' (FMI 5), meaning the internal heating element has failed and the part must be replaced.

4. 4

   Verify that the heater relay/timer relay (pre-heat controller) is sending the correct voltage to the heater when the key is turned to the pre-heat position.

1. 1

   Disconnect Power

   Turn off the tractor and disconnect the negative battery cable to prevent electrical shorts during the repair.

2. 2

   Locate the Heater

   Locate the intake manifold heater (grid heater or thermostart plug) on the engine's air intake manifold.

3. 3

   Disconnect Connections

   Disconnect the electrical wiring harness connector from the heater. (Note: If your specific model uses a traditional thermostart plug rather than a dry grid heater, you will also need to disconnect the small fuel dribble line attached to it).

4. 4

   Remove the Faulty Part

   Unbolt or unscrew the faulty heater element from the intake manifold.

5. 5

   Clean and Prep

   Clean the mounting surface on the intake manifold to ensure a good seal and electrical ground (if chassis-grounded).

6. 6

   Install the New Heater

   Insert the new intake heater and torque it to the manufacturer's specifications.

7. 7

   Reconnect

   Reattach the electrical connections (and fuel line, if applicable).

8. 8

   Clear Codes and Test

   Reconnect the battery. Turn the key to the ON position to allow the ECU to run a self-check, clear the U 699 fault code using a diagnostic tool, and perform a cold start test to verify the heater activates properly.