CCU 001638.04 – Hydraulic Oil Temperature Sensor Circuit Voltage Low

CCU 001638.04 (CCU 1638.04)

Code: 001638.04

Shortcode: 1638.04


This fault code indicates that the Chassis Control Unit (CCU) has detected that the hydraulic oil temperature sensor is shorted to ground, resulting in a low voltage condition. Additionally, it may also occur under specific conditions related to engine speed, hydraulic oil temperature, and engine coolant temperature.


The function of the hydraulic system is degraded to prevent unsafe operation due to unreliable temperature readings.


  • Inspect Sensor and Wiring: Inspect the hydraulic oil temperature sensor and associated wiring for any signs of damage, corrosion, or short circuits to ground. Repair or replace components as necessary.
  • Check Sensor Installation: Ensure that the sensor is installed correctly and securely in the hydraulic system. Adjust or reinstall as needed to prevent grounding.
  • Address Engine Speed and Temperature Conditions: Investigate the specific conditions under which the fault occurs, such as engine speed, hydraulic oil temperature, and engine coolant temperature. Address any discrepancies to prevent false fault triggers.
  • Reset and Retest: After addressing the underlying issues, reset the CCU and perform tests to ensure that the fault code does not recur under normal operating conditions.


Maintaining proper sensor functionality and electrical integrity is essential for accurate temperature monitoring and safe operation of hydraulic systems. Regular inspections and preventive maintenance can help prevent issues related to sensor circuit faults.

Control Units: John Deere

John Deere Parts
John Deere Logo