John Deere 1638 – CCU (Central Control Unit): Transmission Hydraulic Oil Temperature Is Very High

The control unit has detected that the hydraulic/transmission fluid temperature has exceeded the maximum specified safe operating range.

• 5085E
• 5090E
• 5090EL
• 5100E
• 5045E
• 5055E
• 5065E
• 5075E
• 5065M
• 5075M
• 5085M
• 5100M
• 5100MH
• 5100ML
• 5115ML
• 5095M
• 5095MH
• 5105M
• 5015ML
• 5090M
• 5115M
• 444J
• 544J
• 624J
• 844J
• 850J
• 770G
• 872D

1. 1

   Check transmission/hydraulic oil level using the dipstick or sight glass (low fluid is a primary cause)

2. 2

   Visually inspect the transmission/hydraulic oil cooler and front grill for accumulated debris, dirt, or chaff blocking airflow

3. 3

   If the code occurs specifically during transport speeds, inspect the transmission suction screen for plugging

4. 4

   Inspect the transmission scavenge pump for physical damage

5. 5

   If the code is thrown immediately when the tractor is cold (electrical cause), check the wiring harness to the temperature sensor for shorts to power or ground

1. 1

   Reduce Load and Cool Down

   Immediately reduce the load on the machine, park it safely, and allow the engine and hydraulic system to cool down.

2. 2

   Clean the Cooling System

   Use compressed air or a pressure washer to clean out the front grill and the fins of the hydraulic oil cooler.

3. 3

   Top Up Fluid

   If the hydraulic oil is below the acceptable level, fill it to the correct specification using John Deere approved hydraulic fluid (e.g., Hy-Gard).

4. 4

   Clean the Suction Screen

   Drain the hydraulic fluid into a clean container, remove the transmission suction screen, clean it thoroughly with solvent, and reinstall it.

5. 5

   Replace Filters

   If the hydraulic oil filter is restricted (often accompanied by code 1713.00 or 1713.31), replace the filter.

6. 6

   Replace the Sensor

   If the physical temperature of the oil is verified to be normal but the CCU continues to log the 1638.00 code (or if the sensor fails a multimeter resistance test), replace the Transmission/Hydraulic Oil Temperature Sensor and clear the codes.