John Deere 001638.00 – CCU: Transmission Hydraulic Oil Temperature Very High

The hydraulic oil temperature is very high, indicating the fluid is too hot for continued safe operation. This condition can lead to wasted power and potential damage to hydraulic system components such as seals and pumps. The persistence of this code after attempts to clear it suggests an ongoing problem within the hydraulic system that requires immediate attention.

• 5045E
• 5055E
• 5065E
• 5075E
• 5085E
• 5090E
• 5090EL
• 5100E
• 5065M
• 5075M
• 5085M
• 5095M
• 5095MH
• 5105M
• 5015ML
• 7630
• 7730
• 7830
• 7930
• 8230T
• 8330T
• 8430T
• 9230
• 9330
• 9430
• 9530
• 9630
• 450
• 4955
• 4050
• 4250
• 4450

1. 1

   Immediately reduce the load on the tractor's hydraulic system and engine

2. 2

   Check the transmission and hydraulic oil level (both low and overfull levels can cause overheating). For models like the 9530 and 9630, a known issue of being overfull from the factory can cause this code (especially in 18th gear); a specific procedure to lower the oil level by about a gallon may be required. Always follow the precise oil level checking procedure for your specific model.

3. 3

   Inspect the transmission/hydraulic oil cooler and front grill for debris buildup (dirt, chaff, grass) and clean cooling fins using compressed air, a brush, or a rag

4. 4

   Use an infrared thermometer to check the temperature of the transmission housing to confirm if it is genuinely overheating or a sensor issue

5. 5

   Inspect the wiring harness and connectors for the transmission oil temperature sensor for visible damage, corrosion, or loose connections

6. 6

   Check for internal high-pressure hydraulic leaks, which can cause the oil to heat up (may require specialized tools to check pressures in different circuits)

1. 1

   Locate temperature sensor

   Find the transmission hydraulic oil temperature sensor. Location varies by model (e.g., filter cap on lower right side of transmission case for 450 series, or inlet manifold for transmission pump suction tube for 4955).

2. 2

   Test temperature sensor

   With a scan tool on a cold engine, verify the transmission fluid temperature reading is within 5-7°F of the intake air temperature. Alternatively, remove the sensor and measure its resistance with a multimeter while placing it in water of varying temperatures; resistance should change smoothly. A sudden drop, spike, or no change in resistance indicates a faulty sensor.

3. 3

   Test sensor circuit

   Turn ignition on (engine off). Set multimeter to DC voltage and probe the harness connector terminals (not the sensor) to ground. One terminal should show a reference voltage of approximately 5 volts. Lack of voltage indicates a wiring or CCU issue.

4. 4

   Replace temperature sensor

   If the sensor fails the resistance or scan tool tests, replace it with a new OEM part.

5. 5

   Replace hydraulic filters

   If the fault code is accompanied by a hydraulic filter restriction code (e.g., CCU 1713.0), replace the transmission hydraulic oil filters.

6. 6

   Seek professional assistance

   If these steps do not resolve the fault, the issue may be more complex, such as an internal hydraulic leak or a problem with the CCU, and assistance from a qualified John Deere technician is recommended.