John Deere 002850.03 – CRU: High Voltage On Radio Aerial Radio (CRU)

The control module monitoring the radio antenna has detected an abnormally high voltage condition (Voltage Above Normal, or Shorted to High Source) on the Radio Aerial circuit. This indicates a potential short circuit to a power source, a fault within the antenna or its coaxial wiring, or an internal malfunction within the radio control unit itself.

• 5M
• 6M
• 6R
• 7R
• 8R
• 9R
• Loaders
• Combines

1. 1

   Verify battery and charging system voltage using a multimeter (battery should be at least 12.6V, alternator output should not exceed 14.5V).

2. 2

   Inspect the wiring harness and connectors between the radio and the antenna for damage, corrosion, or loose connections. Pay close attention to the power supply wires for the radio.

3. 3

   Check for proper grounding of the radio, ensuring any separate ground wires bundled with the antenna lead are secure.

4. 4

   Review any aftermarket or two-way radio installations to ensure antenna cables are not routed near other controller harnesses and power sources are correctly wired (e.g., red wire #272 for switched operation and red wire #262 for constant battery power).

1. 1

   Clear fault codes

   Disconnect the battery ground cable before beginning electrical repairs. Reconnect, clear the diagnostic trouble codes, operate the machine, and check if the fault code reappears to determine if the issue is currently active.

2. 2

   Isolate the fault

   Disconnect the antenna from the radio. If the high voltage fault code disappears, the issue is likely isolated to the antenna or its cabling.

3. 3

   Test the antenna and coax cable

   Visually inspect the antenna. Use a multimeter to test the coaxial cable for a short (there should be no continuity between the center pin and outer shield). Verify continuity from the center pin at the radio connector to the antenna tip (near zero ohms), and from the outer shield to the vehicle chassis.

4. 4

   Test radio power supply

   With the radio disconnected, check the voltage at the radio's power supply connector. It should be approximately 12V. If the voltage is excessively high, diagnose the machine's electrical system (e.g., a faulty voltage regulator).

5. 5

   Replace faulty components

   Replace the antenna or coaxial cable if they fail the continuity tests. If the radio itself is determined to be the source of the high voltage reading due to an internal failure, replace the radio unit.