John Deere 158.17 – RLC: Switched Supply Voltage Low

The electrical supply voltage to the roof module has dropped below the minimum operating threshold (typically 11 or 11.2 volts) while the engine is active. This points to a charging system failure, a weak battery, excessive electrical load, or high resistance (poor connection) in the wiring supplying the module.

• 6110R
• 6120R
• 6130R
• 6145R
• 6155R
• 6175R
• 6195R
• 6215R

1. 1

   Reduce electrical load by turning off customized or high-draw accessories (flood lights, hazard lights, window wipers) or increase engine RPM to see if the alternator catches up and the code clears.

2. 2

   Check the batteries for physical damage, accumulated debris, and loose or corroded terminals. Test resting voltage (should be ~12.6V).

3. 3

   Test alternator output voltage at the battery with the engine running. It should read between 13.5V and 14.5V. If below 11V-12V, the alternator is not charging.

4. 4

   Inspect the wiring harness leading up to the Cab Roof Module for chafing, pinched wires, or loose ground connections that could cause a voltage drop.

1. 1

   Power Down

   Turn off the engine, remove the key, and shift to PARK.

2. 2

   Clean Connections

   Disconnect the battery cables (negative first). Clean the battery posts and cable terminals with a wire brush. Reconnect and tighten securely.

3. 3

   Test/Replace Battery

   Perform a load test on the battery. If the battery fails to hold a load, replace it.

4. 4

   Test/Replace Alternator

   If the battery is good but the running voltage remains below 11 Volts, inspect the alternator belt for slipping. If the belt is tight and in good condition, the alternator has failed internally and must be replaced.

5. 5

   Circuit Repair

   If both the battery and alternator test within normal specifications, the voltage drop is isolated to the RLC circuit. Trace the power supply wire to the Cab Roof Module, repair any damaged sections, and clean the module's connector pins.

6. 6

   Clear Codes

   Cycle the ignition key to clear the code. Start the engine and verify the code does not return.