Merlo 12 – 15 – MSS: Resistance Out of Range / Short Circuit

The MSS (Modular Indicator Light and Push-button Module) has detected a signal from one of four specific potentiometers that is outside its expected operational range. This indicates a resistance out of range, short circuit, or open circuit in the wiring or the component itself. Fault code 12 corresponds to Potentiometer 1 (Slot 10), 13 to Potentiometer 2 (Slot 11), 14 to Potentiometer 3 (Slot 12), and 15 to Potentiometer 4 (Slot 13). This fault typically results in the loss of function for the associated component, such as the joystick, inching pedal, or telescopic boom.

• Turbofarmer
• Panoramic
• Multifarmer
• Roto

1. 1

   Visually inspect the wiring harness and connectors associated with the joystick, inching pedal, and boom extension sensor for chafed wires, loose connections, or corrosion.

2. 2

   Check for basic electrical issues, ensuring a stable battery supply, good ground connections, and intact main and relevant fuses.

3. 3

   Utilize on-board diagnostics (such as the 'Diagnose MSS' function via MerloDiag) to confirm the active fault code and identify the specific potentiometer.

4. 4

   Check the signal voltage from the suspected potentiometer using a multimeter; the voltage should vary smoothly as the component is moved, whereas a fixed, zero, or erratic reading indicates a fault.

1. 1

   Isolate the faulty potentiometer

   Identify the specific potentiometer based on the fault code (12 for Slot 10, 13 for Slot 11, 14 for Slot 12, 15 for Slot 13). An unresponsive joystick is often the most likely culprit.

2. 2

   Access the component

   For a joystick, lift the rubber boot at the base to access internal components and wiring. For a boom sensor, remove protective covers to access the cable reel mounted on the boom.

3. 3

   Test the component resistance

   Disconnect the potentiometer and test its resistance with a multimeter while actuating the component. An open circuit (infinite resistance) or short circuit (zero resistance) confirms the potentiometer has failed.

4. 4

   Replace the faulty part

   Replace the failed potentiometer, individual joystick buttons, the entire joystick assembly, or the sensor reel as required.

5. 5

   Recalibrate the system

   Use the MerloDiag diagnostic tool to recalibrate the new component so its signal range is correctly interpreted by the control module. Alternatively, a manual calibration procedure may be possible for certain components by putting the machine in a specific mode and moving the component to its minimum and maximum positions.