John Deere 84 – Header / SST: CAN Bus Message Missing from Cornerpost Control Unit - Wheel Speed

The system has detected that a CAN Bus message from the Cornerpost Control Unit related to wheel speed is missing. This indicates a communication breakdown on the CAN bus between the Cornerpost Control Unit and the receiving control unit (such as the Header or SST unit). This loss of information disrupts machine functions that rely on accurate speed readings and can be caused by wiring issues, faulty control units, or a defective wheel speed sensor.

• 9450
• 9540
• 9550
• 9550SH
• 9560
• 9560STS
• 9580
• 9640
• 9650
• 9650CTS
• 9650STS
• 9660
• 9660CTS
• 9660STS
• 9680
• 9750
• 9750STS
• 9760
• 9760STS
• 9780
• 9860 STS
• 8000 Series
• 8130
• 8230
• 8330
• 8430
• 8530
• 7000 Series
• 2204 Series
• 6M Series
• 6R Series
• 7M Series
• 8R Series
• 8RT Series
• 8RX Series
• 6B Series
• 6E Series

1. 1

   Record and clear codes using the machine's diagnostic display, then operate the machine to see if fault code 84 immediately returns.

2. 2

   Visually inspect the wiring harnesses and connectors associated with the Cornerpost Control Unit, the logging control unit, and the wheel speed sensors for signs of damage, corrosion, or loose connections.

3. 3

   Perform a cold boot by turning the key switch to the OFF position and waiting for at least 30 seconds before restarting to see if the communication error resets.

1. 1

   Check CAN bus voltages

   With the key on and the engine off, use a multimeter to check the CAN bus voltages at a diagnostic connector. The CAN High wire (typically yellow) and CAN Low wire (typically green) should both read approximately 2.5 volts. Deviations indicate a short or open in the CAN bus wiring.

2. 2

   Inspect wheel speed sensor

   Locate the wheel speed sensor (on many 8000 series tractors, it is on top of the rear axle housing). Inspect for physical damage, debris buildup, and check the wiring and connector leading to the sensor.

3. 3

   Test wheel speed sensor

   Test the sensor's output with a multimeter or a specialized diagnostic tool to ensure it is generating a signal as the wheel rotates.

4. 4

   Check Cornerpost Control Unit connections

   Disconnect the main connector (often labeled X500) from the Cornerpost Control Unit, inspect the pins for corrosion or damage, and reconnect it securely.

5. 5

   Isolate the faulty component

   If the CAN bus wiring and sensor are in good condition, use an advanced diagnostic tool or temporarily substitute a known good control unit to determine if the Cornerpost Control Unit or the logging control unit is faulty.

6. 6

   Calibrate the wheel speed sensor

   If a wheel speed sensor or a related control unit is replaced, perform a calibration procedure by driving the machine over a measured distance at a constant speed to allow the system to learn the correct sensor values.