John Deere CCU001638.00 – CCU: Transmission/Hydraulic Oil Cooler Overheating

The hydraulic oil temperature has exceeded the normal operating range and is considered extremely high. This condition indicates that the fluid is too hot for continued safe operation, which can lead to severe damage to seals, pumps, and other components within the hydraulic and transmission systems.

• 5085M
• 5090M
• 5100M
• 5115M
• 6100D
• 6115D
• 6R Series
• 9x20 Series

1. 1

   Immediately reduce the workload of the tractor to allow the system to cool

2. 2

   Check the hydraulic oil level when the oil is cold and the engine is not running (low oil can trigger this code)

3. 3

   Inspect the front grill, radiator, and transmission/hydraulic oil cooler for debris buildup that could obstruct airflow

4. 4

   Inspect the hydraulic oil filter for clogs or restrictions (check for metallic particles or related code CCU 1713.0)

5. 5

   Check for internal or external hydraulic leaks that could lead to low oil levels and overheating

6. 6

   Test the hydraulic oil temperature sensor and its wiring circuit for faults if no physical overheating cause is found

1. 1

   Clean the oil cooler

   Safely park the machine and allow it to cool down. Open the hood and clean the cooling fins of the hydraulic oil cooler using a rag, brush, or compressed air (reduced to a safe pressure of 30 psi) to remove all debris.

2. 2

   Service hydraulic oil and filter

   If the oil is old, contaminated, or the filter is clogged, place a container under the hydraulic oil filter and drain plug. Loosen the filter to drain oil from the tank, then remove the old filter and the drain plug. Apply a film of clean oil to the new filter gasket, install it, and tighten 1/2 to 3/4 of a turn after contact. Reinstall the drain plug and refill the reservoir with John Deere Hy-Gard hydraulic oil. Start the engine, check for leaks, and cycle hydraulic functions.

3. 3

   Replace faulty components

   If diagnostics point to a faulty temperature sensor or a damaged oil cooler, replace the affected component. For complex issues like a plugged oil cooler bypass valve, internal hydraulic leaks, or a failed transmission pump, dealer service is recommended.