CLAAS Id781Ah / 781Ah – HYD (A60): Value of the position sensor is too low

The signal voltage returning from the front lifting position sensor has dropped below the minimum acceptable threshold. When this occurs, the front lifting system may operate without position checking, or the tractor will return to normal mode only once the correct voltage is restored.

• CLAAS Axion 800 Series (810, 820, 830, 840, 850)
• CLAAS Axion 900 Series (920, 930, 940, 950, 960)
• CLAAS Xerion Series (3300, 3800)

1. 1

   Inspect the front lifting position sensor (Component ID: B139-1) and the hydraulic module (A60).

2. 2

   Check the connectors and the continuity of the wiring harnesses linking the B139-1 sensor to the A60 module.

3. 3

   Check for any short-circuits to ground or open circuits in the sensor's signal and supply wires.

4. 4

   Check the sources of energy (fuses, 5V reference supply, and ground).

5. 5

   Check the component's operating conditions, specifically looking for mechanical seizing or improper adjustment of the sensor linkage.

6. 6

   Check the sensor's internal resistance if required.

1. 1

   Verify the Fault

   Note the error codes present on the tractor's CEBIS terminal and verify if Id781Ah is currently active.

2. 2

   Visual & Mechanical Inspection

   Locate the front lifting position sensor (B139-1) on the front linkage assembly. Inspect the mechanical linkage rod connecting the sensor to the lift arms for damage, bending, or seizing.

3. 3

   Electrical Testing

   Disconnect the B139-1 sensor. Inspect the pins for corrosion or moisture. Turn the ignition on and use a multimeter to verify that the HYD (A60) module is sending the correct reference voltage (typically 5V) and a good ground to the sensor connector.

4. 4

   Harness Continuity

   If power and ground are missing, trace the harness back to the A60 module to repair the open/shorted wire.

5. 5

   Sensor Replacement

   If the wiring, power, and ground are all intact but the signal voltage remains too low, the B139-1 sensor has failed internally and must be replaced.

6. 6

   Calibration

   After installing the new sensor, you must connect the CLAAS Diagnostic System (CDS) and perform the "Front lifting position sensor" calibration routine.

7. 7

   Clear Codes

   Clear all error codes and test the front linkage through its full range of motion to ensure the anomaly does not return.