John Deere 1638.16 – CCU: Transmission Hydraulic Oil Temperature Is High

The hydraulic oil temperature sensor has detected fluid temperatures that are higher than normal operating levels, but have not yet reached a critically hot threshold. The control unit responds by degrading the function of the hydraulic system to prevent damage.

• 5085E
• 5090E
• 5090EL
• 5100E
• 5045E
• 5055E
• 5065E
• 5075E
• 5065M
• 5075M
• 5085M
• 5100M
• 5100MH
• 5100ML
• 5115ML
• 5095M
• 5095MH
• 5105M
• 5015ML
• 5090M
• 5115M
• 4730
• 4830

1. 1

   Check hydraulic oil level at the rear differential sight glass (low fluid is a primary cause)

2. 2

   Inspect the transmission/hydraulic oil cooler and general cooling system for debris, dirt, or blockages

3. 3

   If the code only occurs during transport speeds, inspect the transmission suction screen for plugging and the transmission scavenge pump for damage

4. 4

   Check the hydraulic oil filter for restriction causing fluid bypass

1. 1

   Reduce Load

   Immediately reduce the load on the tractor to prevent further heat buildup.

2. 2

   Clean the Cooler

   Thoroughly clean any chaff, mud, or debris from the hydraulic/transmission oil cooler and radiator fins.

3. 3

   Top Up Fluid

   Check the hydraulic oil level. If it is low, fill it to the correct level using approved John Deere Hy-Gard transmission/hydraulic oil.

4. 4

   Test Operation

   Restart the vehicle and operate it at a nominal speed for 1 to 2 minutes.

5. 5

   Filter Replacement

   If the CCU 1638.16 code returns after cleaning the cooler and topping up the fluid, replace the hydraulic oil filter.

6. 6

   Inspect Suction Screen

   Drain the hydraulic fluid and remove/inspect the transmission suction screen. Clean it thoroughly if it is plugged with sludge or metal shavings.

7. 7

   Sensor Verification

   If the system is mechanically sound, fluid is full, and the cooler is clean, the hydraulic oil temperature sensor or its wiring harness may be faulty (shorted or degraded). Test the sensor's resistance and verify the wiring to the CCU.

8. 8

   Dealer Service

   If the code persists after these steps, contact a John Deere dealer, as the transmission scavenge pump may be damaged or there may be an internal hydraulic leak causing excessive friction.