John Deere 444.03 – RLC (Roof Lighting Controller / Cab Roof Module): Control Software, Supply Voltage (BAT at Terminal J4) Too High

The voltage being supplied to the module has exceeded normal operating parameters (typically over 16 volts), which is usually caused by an overcharging alternator or a short circuit to a high-voltage source.

• 6110R
• 6120R
• 6130R
• 6145R
• 6155R
• 6175R
• 6195R
• 6215R
• 6230
• 6330
• 6430
• 5085M
• 5100M
• 5115M
• 8245R to 8400R
• 9470RT
• 9520RT
• 9570RT
• 770G
• 772G
• 9650

1. 1

   Verify Charging System: Check the alternator and voltage regulator for proper operation while the engine is running. An output of over 15-16 volts indicates the voltage regulator has failed and is overcharging the system.

2. 2

   Inspect Electrical Connections: Inspect all electrical connections at the RLC (specifically Terminal J4), as well as the battery and alternator. Ensure they are clean, secure, and free from corrosion.

3. 3

   Check Battery Health: Test the battery to ensure it is in good condition. A severely degraded or internally shorted battery can sometimes cause the alternator to overcompensate.

4. 4

   Examine Wiring: Inspect the wiring harness for any signs of wear, damage, or melted insulation that could be causing a short circuit to a high-voltage source.

1. 1

   Test and Replace the Alternator/Regulator

   If diagnostic testing confirms the alternator is outputting excessive voltage (over 16V), remove the drive belt, disconnect the battery, and replace the alternator (or the internal voltage regulator, if serviceable separately).

2. 2

   Clean Connections

   Disconnect and clean the battery terminals, the main alternator charge post, and the RLC Terminal J4 connector. Reconnect them securely.

3. 3

   Repair Wiring

   If the alternator is testing within normal limits (13.5V - 14.5V) but the RLC is still seeing high voltage, trace the wiring harness from the RLC back to the power distribution center. Repair or replace any compromised wiring causing a short.

4. 4

   Clear Codes

   Cycle the key switch or use the CommandCenter™ / diagnostic tool to clear the fault code and verify the repair.