Case IH 13250 – TIM Server/Client ECU: Reflected request counter / Bus-Off

SPN 13250 translates to the 'Reflected request counter' used in Tractor Implement Management (TIM) communications. A 'Bus-Off' state occurs when a CAN node's Transmit Error Counter (TEC) exceeds 255 due to repeated transmission failures (often caused by wiring shorts, bad grounds, or missing terminators), causing the node to completely disconnect from the ISOBUS network.

• MAXXUM T4E
• Vestrum CVXDrive
• Maxxum
• Puma
• Optum CVXDrive
• Magnum
• Steiger/Quadtrac series
• LB4 XL large square balers
• LB6 HD large square balers
• RB455 round balers
• RB465 round balers

1. 1

   Check AFS display diagnostics for CAN Bus Utilization (should be below 25%), BUS Off Count, and Overrun Error Count to confirm which node is dropping

2. 2

   Inspect the ISOBUS 9-pin breakaway connector at the rear of the tractor and the implement plug for dirt, corrosion, or bent pins

3. 3

   Verify CAN voltages using a multimeter: Yellow (CAN-Hi) and Green (CAN-Lo) combined voltage should equal approximately 5V against CAN ground

4. 4

   Check terminating resistors with the battery disconnected: resistance across CAN-Hi and CAN-Lo pins should read exactly 60 ohms

5. 5

   Ensure the implement ECU is receiving a stable power supply above 12V to prevent voltage drops and resets

1. 1

   Power Down

   Turn off the tractor ignition and disconnect the battery to ensure the network is completely powered down.

2. 2

   Clean and Secure Connections

   Spray the tractor's rear ISOBUS receptacle and the implement's plug with electrical contact cleaner. Ensure the plug seats firmly and the locking collar engages.

3. 3

   Resolve Terminator Issues

   If your resistance test showed improper termination (e.g., 120 ohms or 40 ohms), locate the terminating resistors. Ensure that only the two physical ends of the CAN bus are terminated. If an implement's internal jumper (between pins 4 and 5) is failing to disable a redundant terminator, the implement ISO plug may need to be replaced.

4. 4

   Repair Harness Damage

   Trace the Yellow and Green CAN wires along the implement drawbar and tractor chassis. Repair any chafed wires that are shorting to the frame (ground) or to each other, which is the primary cause of a TEC exceeding 255.

5. 5

   Hardware Reset

   Reconnect the battery and cycle the ignition key to reboot the ECUs and restore them to an 'error-active' state.

6. 6

   Software Update

   Check the AFS display and implement ECU for firmware updates. Outdated software can cause TIM protocol mismatches that lead to message collisions and bus-off events.