Massey Ferguson AC25 – Air Conditioning Control Module: Vehicle speed error

The Air Conditioning Control Module is not receiving the expected vehicle speed data over the CAN BUS network.

• 7616
• 5612
• 7622
• Interim Tier 4 (2012-2015)
• 7614
• 5611
• 7615
• 5610
• 5613
• 7620
• 5609
• 7618
• 5608
• 7619
• 7626
• 7624
• 7600 Series
• 8600 Series
• 8670
• 8690

1. 1

   Verify Vehicle Speed Sensor (VSS) operation by checking if the tractor's speedometer is working on the main instrument cluster. If dead, the AC module is a victim of a broader CAN bus or speed sensor failure.

2. 2

   Inspect the Air Conditioning Control Module connectors (X439 blue and X440 yellow) for loose pins, moisture intrusion, or corrosion.

3. 3

   Perform a CAN Bus continuity test using a multimeter to check the resistance across the CAN High and CAN Low pins at the AC module connector (should read approximately 60 ohms if healthy).

1. 1

   Power Down

   Turn off the tractor and disconnect the negative battery cable to prevent electrical shorts.

2. 2

   Access the AC Module

   Remove the interior cab roof paneling or side console trim (depending on the specific cab configuration) to expose the Air Conditioning Control Module.

3. 3

   Clean and Reseat Connectors

   Disconnect the X439 (blue) and X440 (yellow) connectors. Spray both the module receptacles and the harness plugs with a high-quality electrical contact cleaner.

4. 4

   Repair Wiring (If Applicable)

   If you found chafed wires or broken pins on the CAN lines during your diagnostic checks, splice in a new section of wire or repin the connector using an OEM pigtail kit.

5. 5

   Reassemble and Clear Codes

   Reconnect the module, restore battery power, and turn the ignition on. Clear the stored AC25 fault code using a diagnostic tool or the tractor's onboard diagnostic menu.

6. 6

   Module Replacement (Last Resort)

   If the wiring is perfectly intact, the instrument cluster shows vehicle speed, but the AC25 code immediately returns, the CAN transceiver inside the Air Conditioning Control Module has failed. The module must be replaced and potentially calibrated by a dealer.