John Deere 001079.03 – CCU: Sensor Supply Voltage High

The fault code 001079.03 indicates that a control unit has measured an abnormally high voltage on the 5-volt reference circuit it provides to its sensors. The .03 Failure Mode Identifier (FMI) specifies that the voltage is above normal or shorted to a high source, typically exceeding a predefined threshold such as 5.2 volts. This over-voltage condition suggests a short circuit to a power source within the electrical system, which compromises the regulated 5V DC supply. As a result, the data sent back to the controller by the affected sensors becomes unreliable, leading to potential operational issues.

• 5225
• 5325
• 5425
• 5525
• 5603
• 5625
• 5085E
• 5095E
• 5100E
• 6120-6420
• 6120L-6520L
• 7610
• 7710
• 7810
• 8130
• 8230
• 8330
• 8430
• 8530
• 8230T
• 8330T
• 8430T
• 8225R
• 8245R
• 8270R
• 8295R
• 8320R
• 8345R
• 9120
• 9220
• 9320
• 9420
• 9520
• 9230
• 9330
• 9430
• 9530
• 9630
• 318D
• 320D

1. 1

   Restart the tractor to see if the fault code is temporary and clears on its own

2. 2

   Access the diagnostic menu to clear active fault codes, cycle the key, and operate the machine to see if the code returns

3. 3

   Conduct a thorough visual inspection of the wiring harnesses connected to the sensors of the affected control unit, looking for chafing, corrosion, loose connections, or areas rubbing against the frame

4. 4

   Isolate the faulty component by turning the key off, unplugging all associated sensors, and turning the key back on. If the code clears, plug sensors back in one at a time (cycling the key each time) until the fault returns to identify the problematic sensor

1. 1

   Confirm and isolate fault

   Use the diagnostic isolation check (unplugging sensors one by one) to confirm if a specific sensor or circuit is causing the high voltage issue.

2. 2

   Consult Technical Manual

   Refer to the official John Deere Technical Manual for your specific machine model to access detailed diagnostic trees, wiring diagrams, and connector pinouts.

3. 3

   Repair or replace wiring harness

   If diagnostics point to a wiring issue (e.g., a short to power), repair the damaged section of the harness or replace it entirely if damage is extensive. In one documented case involving a John Deere 9330, replacing the shift harness resolved an ACU 1079.03 code.

4. 4

   Replace faulty sensor

   If the isolation test identifies a specific sensor causing the voltage spike, replace the faulty sensor.

5. 5

   Replace control unit

   If the wiring and all associated sensors are confirmed to be in good working order, the internal control unit may be faulty and require replacement.