John Deere CAB523624 – CAB: Warning Lighting System-Road Diagnostics Fault

The Cab Control Unit (CAB) has detected an electrical fault in the Warning Lighting System - Road Diagnostics, specifically related to cab roof lights 3 and 4. Depending on the accompanying Failure Mode Indicator (FMI), this indicates that the lights are stuck on due to a short to power (FMI 03), have an open circuit or burnt-out bulb (FMI 05), or fail to turn on when commanded due to a faulty bulb, bad connection, or power supply issue (FMI 06).

• 9570 STS
• 9670 STS
• 9770 STS
• 9870 STS
• A9970

1. 1

   Access the diagnostic trouble codes, note them, clear them, and then operate the lights to see which codes reappear.

2. 2

   Visually inspect cab roof lights 3 and 4, their connectors, and the visible wiring harness for damage, corrosion, loose connections, or burnt-out bulbs.

3. 3

   Operate the cab roof lights from the operator's station to determine the failure mode: lights failing to turn on aligns with FMI 05 or 06, while lights refusing to turn off aligns with FMI 03.

4. 4

   If FMI 05 (Open Circuit): Use a multimeter to check for continuity along wiring harness circuit cc# 584 from the CAB control unit to the lights, and test the bulbs.

5. 5

   If FMI 06 (Off When Commanded On): Verify that voltage is reaching the light connector when the switch is activated. Lack of voltage points to wiring or the CAB controller's output driver.

6. 6

   If FMI 03 (On When Commanded Off): Inspect the wiring harness for chafed or damaged wires causing a short to a power source.

1. 1

   Park safely

   Park the machine on a level surface, lower all implements, shut down the engine, and engage the parking brake.

2. 2

   Access the lights

   Gain access to cab roof lights 3 and 4. This may require removing a portion of the cab headliner or external covers.

3. 3

   Inspect and test bulbs

   Remove the bulbs from the sockets. Visually inspect the filaments and test for continuity with a multimeter, or replace with known good bulbs to rule them out.

4. 4

   Clean and secure connections

   Disconnect the wiring harness from the light assemblies. Clean the terminals with electrical contact cleaner and ensure the connection is secure when reassembled.

5. 5

   Repair or replace wiring

   If diagnostics indicate an open circuit (FMI 05) or a short (FMI 03), trace wiring harness circuit cc# 584 back to the CAB controller. Repair any breaks, chafed spots, or loose connections.

6. 6

   Replace the light assembly

   If the bulbs and wiring are confirmed good but the light still fails to operate correctly (especially for FMI 06), replace the entire light assembly.

7. 7

   Clear fault codes

   After completing the repairs, use the machine's diagnostic system to clear the CAB 523624 fault code.

8. 8

   Verify the repair

   Turn the machine on and operate the cab roof lights to confirm that they now function as commanded and that the fault code does not reappear.