John Deere 158 – Cab Roof Module (RLC) / Cab Load Center (CLC): System Voltage Very High / Overvoltage

Indicates a System Voltage Very High or Overvoltage condition. The underlying condition is almost always an overcharging alternator (a failed voltage regulator) or a severe wiring issue causing excessive voltage to be fed to the control modules.

• 6110R
• 6120R
• 6130R
• 6145R
• 6155R
• 6175R
• 6195R
• 6215R
• 9230-9630 series tractors
• 370E articulated dump truck
• 410E articulated dump truck
• 460E articulated dump truck
• 640H skidder
• 648H skidder
• STS combines

1. 1

   Visually inspect for damage, corrosion, or an accumulation of debris around the battery and the alternator.

2. 2

   Check all alternator wiring and battery connections to ensure they are tight and undamaged.

3. 3

   Use a multimeter to test the voltage at the battery terminals while the engine is running. If the voltage is steadily climbing past 15.5V (or 18V+ on 24V systems), the alternator's internal voltage regulator has failed.

4. 4

   Determine if the Diagnostic Trouble Code (DTC) periodically 'goes away' or if it is a hard, constant fault.

1. 1

   Shut Down

   If this code appears while operating, safely park the machine and shut off the engine immediately to prevent the overvoltage from frying sensitive control modules (like the RLC or ECU).

2. 2

   Clean and Secure

   Clean any debris from the battery and alternator area. Tighten any loose battery cables or alternator harness connections.

3. 3

   Restart and Verify

   Start the vehicle again. If the code returns immediately and the multimeter confirms high voltage, the alternator must be replaced.

4. 4

   Replace Alternator

   Disconnect the battery. Remove the serpentine/drive belt, disconnect the electrical harness from the alternator, and unbolt the alternator from its mounting bracket. Install the new alternator, reattach the wiring, and reinstall the belt.

5. 5

   Clear Codes

   Reconnect the battery, start the tractor, and verify that the charging voltage has returned to a normal range (typically 13.5V - 14.5V for a 12V system). Clear the stored codes using a John Deere diagnostic tool or monitor.