Case IH PB0 – Central Controller (XCM) / Engine Control Module (ECM): Vehicle CAN Chip, Shorted To Low Source

The CAN bus chip has detected a short to ground (low source) on the vehicle's CAN bus network. This specifically indicates a faulty connection or communication breakdown between the central controller (XCM) and the engine control module.

• MXM
• MXM Series
• MXM 120
• MXM 130
• MXM 135
• MXM 140
• MXM 155
• MXM 175
• MXM 190

1. 1

   Perform a visual and harness wiggle test on the harness and connectors between the central controller and the engine control module.

2. 2

   Measure voltage between connector C273 pin 1 (wire 5420–G) and ground, and connector C273 pin 2 (wire 5400–Y) and ground while wiggling the harness to check for an intermittent short circuit.

3. 3

   Verify that the CAN BUS wires (Y and G) are properly twisted together and routed free from possible electromagnetic interference.

4. 4

   Reconnect connector C316 and measure the resistance between connector C273 pin 1 (5420–G) and C273 pin 2 (5400–Y). You are looking for a reading of approximately 120 Ohms.

1. 1

   Repair, reposition, or replace the wiring harness

   If a voltage is indicated during the ground test, or if the CAN BUS wires are not twisted/shielded properly, repair, reposition, or replace the wiring harness as required.

2. 2

   Remove and replace the Engine Control Module

   If the resistance measured is not approximately 120 Ohms, the CAN BUS terminating resistor inside the module has failed. You must remove and replace the Engine Control Module.

3. 3

   Remove and replace the fuel injection pump

   If the resistance indicated is approximately 120 Ohms, the CAN BUS terminating resistor in the engine control module is functioning correctly. The fault is further down the communication line, and you must remove and replace the fuel injection pump.