John Deere CAB746 – CAB: CAB Low Side Driver Short to Power

The CAB control unit has detected voltage on a circuit when its low-side driver (ground switch) is commanded OFF. This abnormal condition indicates a short to a power source in the wiring harness or the controlled component, preventing the controller from properly interrupting the path to ground to turn the component off.

• 9570 STS
• 9670 STS
• 9770 STS
• 9870 STS
• 7830

1. 1

   Record and clear codes on the machine's display, then operate the machine to confirm if the fault is currently active.

2. 2

   Visually inspect wiring harnesses connected to the CAB control unit for chafing, melting, pinch points, or rodent damage, especially near headliners or behind plastic panels.

3. 3

   Check related fuses in the main fuse center (e.g., fuse F18 on 9870 STS combines, which powers the CAB, cornerpost display, and radio).

1. 1

   Identify specific circuit

   Use John Deere Service ADVISOR to identify the specific function (e.g., a particular light or solenoid) triggering the fault. Disconnect this suspect component from the harness.

2. 2

   Test for short to power

   With the component disconnected and the key in the ON position (engine off), use a multimeter to measure voltage between the suspect ground-switched wire in the harness and a known good chassis ground. A reading of voltage (especially 12V) confirms a short to power.

3. 3

   Repair wiring harness

   If a short is confirmed, locate and repair the damaged section of the harness. Solder the repaired wires and seal with heat-shrink tubing. Avoid using simple butt connectors in areas exposed to vibration or moisture.

4. 4

   Replace faulty component

   If the wiring harness tests good (0 Volts measured in step 2), the internal circuitry of the disconnected component is likely shorted. Replace the component.

5. 5

   Replace CAB control unit

   If both the wiring and the component test good, the internal low-side driver transistor has likely failed. Replace the CAB control unit. Clear codes and verify the repair. A new controller may require programming or calibration by a dealer using Service ADVISOR.