Case IH tB1 – Transmission Control Module (TCM) / Electronic Control Unit (ECU): Vehicle CAN Chip, Shorted To High Source

A critical communication failure on the tractor's Controller Area Network (CAN) bus. The CAN transceiver chip inside the control module is detecting a short circuit to a high voltage source (typically 12V battery power), preventing the module from transmitting or receiving valid CAN messages.

• MXM
• MXM 120
• MXM 130
• MXM 140
• MXM 155
• MXM 175
• MXM 190
• TM115 through TM190

1. 1

   Inspect the main transmission wiring harness for chafing, melted insulation, or pinch points that could cause the CAN High or CAN Low wires to short against a 12V power supply wire.

2. 2

   Disconnect the Transmission ECU and inspect the pins. Look for bent pins, corrosion, or moisture ingress that could bridge a power pin to a CAN communication pin.

3. 3

   Isolate the short: With the ECU disconnected and the key ON, use a multimeter to measure the voltage on the harness-side CAN pins. If you see 12V on the CAN lines, the short is in the wiring harness. If the voltage is normal (typically around 2.5V) or zero with the battery disconnected, the short is internal to the ECU's CAN chip.

1. 1

   Disconnect Power

   Disconnect the tractor's battery to prevent further electrical damage.

2. 2

   Repair Wiring

   If a short to power was found in the harness during diagnostics, repair the damaged wire, re-loom the harness, and clear the codes.

3. 3

   Replace the ECU

   If the harness tests good, the CAN chip inside the Transmission ECU has failed. Remove the faulty Transmission ECU and install the replacement module.

4. 4

   Perform Calibration

   Warm the tractor up, apply the handbrake, lower all equipment to the ground, and block the wheels. Hold the High and Low range buttons and start the engine. 'CAL' will appear on the transmission display. Set the engine speed to 1200 RPM. Follow the H-Menu prompts to calibrate the clutches until 'END' is displayed.