CLAAS 768Bh – Auto 5: Rear PTO Speed Sensor Fault

The control unit has detected an anomaly in the signal from the rear PTO speed sensor. This can be caused by a complete loss of signal, an erratic signal, or a conflict between the PTO speed data and engine speed. The system relies on this sensor to monitor PTO engagement and rotational speed; a failure will often cause the PTO to fail to engage or to disengage unexpectedly for safety.

• Arion 500
• Arion 600
• Arion 800
• Axion 800
• Axion 850
• Axion 950

1. 1

   Visually inspect the wiring harness and connectors leading to the rear PTO speed sensor for damage, corrosion, moisture ingress, or loose connections (especially under the cab or near the rear).

2. 2

   Check for other active fault codes that might indicate a broader Powertrain CAN bus network communication issue.

3. 3

   Verify CAN Bus communication; if the 'EXT' module is not receiving rear PTO information, check the 'CLAAS vehicle CAN Bus' network.

4. 4

   Remove the PTO speed sensor (magnetic pickup) and clean any metallic debris accumulated on the sensor tip.

5. 5

   Perform a basic system test: engage the PTO and observe if it engages momentarily before shutting down, which strongly points to a lack of speed sensor feedback.

1. 1

   Identify components

   Locate the rear PTO speed sensor (designations B142, B228-1, or B227), the 'Auto 5' PTO control module (typically at the rear of the cab under the SMV cover), and the rear PTO solenoid valve (Y325).

2. 2

   Test PTO speed sensor

   With the tractor off, measure the sensor's internal resistance using a multimeter. Alternatively, back-probe the connector to read the AC voltage signal while the PTO shaft is rotated. Compare readings to the service manual specifications.

3. 3

   Test PTO solenoid

   Check the resistance of the PTO solenoid coil (Y325). If within spec, cautiously apply 12V directly to the solenoid (ensuring correct polarity if a diode is present) and listen for a mechanical 'click'.

4. 4

   Inspect wiring continuity

   Check the continuity of the wiring harness between the speed sensor, the control module, and the solenoid. Test for any short circuits to ground or to power.

5. 5

   Evaluate control module

   If the sensor, solenoid, and wiring are confirmed to be in good working order, the fault may lie within the control module itself. Use a CLAAS diagnostic tool to further test the 'Auto 5' unit.