Merlo 442 – 445 – UGS / MD-CODER: Pressure Sensor Supports Outside Limits

The main hydraulic and safety control unit has detected a signal from an outrigger (stabilizer) pressure sensor that is outside the acceptable operational range. The sensor is reporting a value of either 0 (indicating an open circuit) or 255 (indicating a short circuit). Because these sensors monitor hydraulic cylinder pressure to ensure the machine is level and stable, this fault will trigger the safety system and prevent operations such as boom extension or rotation.

• Roto 40.25 MCSS
• Roto 50.35
• Panoramic
• Turbofarmer
• Multifarmer

1. 1

   Visually inspect the wiring harness leading to the outrigger pressure sensors for chafing, pinched wires, or corroded connectors.

2. 2

   Isolate the faulty component by swapping electrical connectors between two outrigger pressure sensors (e.g., rear left and rear right). If the fault code changes to the other side, the sensor is faulty; if it remains, the issue is in the wiring or control module.

3. 3

   Use a multimeter to test the continuity of the wiring from the sensor back to the UGS control module, checking for open circuits or shorts to ground.

4. 4

   Verify the control module and sensor circuits are receiving the correct and stable power supply voltage.

5. 5

   Use MerloDiag or MerloTOOL diagnostic software to read live sensor data and confirm the fault.

1. 1

   Depressurize hydraulic system

   Ensure the machine is parked on level ground with the engine off. Operate the hydraulic controls to discharge any residual pressure in the system.

2. 2

   Locate the faulty sensor

   Identify the specific outrigger pressure sensor triggering the code on the hydraulic cylinder (e.g., code 445 often corresponds to the rear left outrigger).

3. 3

   Inspect and clean connector

   Disconnect the electrical connector from the sensor. Clean the contacts and inspect for damage or corrosion. Re-test to see if the connection was the issue.

4. 4

   Replace pressure sensor

   If diagnostics point to a failed sensor, unscrew the old sensor from the hydraulic line (be prepared for a small amount of hydraulic oil to leak). Install the new sensor, tighten to the correct torque specification, and reconnect the wiring.

5. 5

   Repair wiring harness

   If the sensor swap test or continuity test indicated a wiring fault, repair or replace the damaged section of the harness.

6. 6

   Inspect control module

   If sensors and wiring are intact but the fault persists, the UGS control module itself may be faulty. Replacement requires configuration by a certified dealer.

7. 7

   Calibrate new sensor

   Using a dealer-level diagnostic tool, perform a calibration to input offset and gain values specific to the new sensor to ensure accurate safety system readings.

8. 8

   Final system check

   Start the machine, clear the fault codes, and test the function of all outriggers and the safety system to ensure the fault has been resolved.