John Deere 1639.01 – ECU: Fan Speed Signal Missing

The control module is commanding the cooling or intercooler fan to spin, but it is either not receiving a rotational speed signal back from the fan speed sensor, or the detected speed is severely below the expected operating range. This is a severe level fault that can lead to engine derating or prevent the machine from completing an exhaust regeneration cycle.

• 5085E
• 5090E
• 5090EL
• 5100E
• 5085M
• 5100M
• 5100MH
• 5100ML
• 5115ML
• 5090M
• 5115M
• 6110M
• 6120M
• 6130M
• 6145M
• 6155M
• 6175M
• 6195M
• 6110R
• 6120R
• 6130R
• 6145R
• 6155R
• 6175R
• 6195R
• 6215R
• 5080R
• 5090R
• 5100R
• 7830
• 9530
• 9470RT
• 9520RT
• 9570RT
• 160G
• 470GLC
• 470P
• R4023
• 4630
• 310K

1. 1

   Check the fan drive system mechanically. Ensure there are no physical obstructions preventing the fan from turning and that the drive belts or hydraulic drive motors are functioning properly.

2. 2

   For hydraulically driven fans, verify that the bleed screw under the fan drive is fully closed.

3. 3

   Inspect the wiring harness between the fan speed sensor and the ECU. Look for chafed wires, loose connections, or corroded pins.

1. 1

   Power Down

   Turn off the machine and ensure the engine is cool before working near the cooling package.

2. 2

   Inspect the Fan Drive

   Visually inspect the intercooler/engine cooling fan. If it is belt-driven, check for belt slippage or breakage. If it is a hydraulic proportional fan, check for hydraulic leaks or a failing proportional solenoid valve.

3. 3

   Check the Bleed Screw

   Locate the bleed screw on the fan drive (if equipped) and tighten it to ensure it is fully closed.

4. 4

   Test the Sensor Wiring

   Disconnect the fan speed sensor. Use a multimeter to check for continuity between the sensor connector and the ECU pins. Repair any broken wires or replace damaged connector pigtails.

5. 5

   Replace the Sensor

   If the mechanical drive is sound and the wiring harness tests good, the fan speed sensor itself has likely failed internally and must be replaced.

6. 6

   Clear Codes and Test

   Install the new sensor, clear the ECU fault codes, and run the engine. Verify that the ECU is now reading the fan speed and that the machine does not derate.