Case IH P39 – Engine Control Module (ECM) or Central Controller (XCM): Vehicle CAN Bus Transmit, Shorted To High Source

The CAN bus transmit circuit is experiencing a short circuit to a high voltage source (such as battery voltage), which disrupts normal communication across the vehicle's network. When this code is active, the engine is typically still enabled with no restriction on fuel or speed.

• MXM
• MXM120
• MXM130
• MXM140
• MXM155
• MXM175
• MXM190

1. 1

   Check for a faulty connector at the ECM and XCM

2. 2

   Check for a faulty wiring harness (specifically looking for a short to a high source or short to ground)

3. 3

   Check for external CAN BUS interference

4. 4

   Check for a software conflict between the Central Controller (XCM) and the Engine Control Module software

5. 5

   Verify if the Engine Control Module is faulty

6. 6

   Verify if the Central Controller (XCM) is faulty

1. 1

   Check for an intermittent circuit

   Turn the keystart OFF. Wiggle the harness and connectors. If an unexpected voltage is indicated on the CAN lines, repair or replace the harness as required.

2. 2

   Check for a short circuit or short to ground

   With the keystart OFF, check the continuity between the ECM/XCM connectors (e.g., C270 pin 4 and C270 pin 3; C270 pin 4 and C270 pin 1; C270 pin 4 and ground). Wiggle the harness and the connectors to check for an intermittent circuit. If a short circuit or short to ground is indicated, repair or replace the harness.

3. 3

   Check for an open circuit

   Measure the resistance between the corresponding pins on the harness connectors (e.g., C270 pin 4 and C316 pin 12). Wiggle the harness and connectors. If the resistance indicated is greater than 5 Ohms, repair or replace the harness.

4. 4

   Software Update

   If the harness tests okay and no shorts or high resistance are found, download the correct (updated) level of software into the Engine Control Module to resolve potential XCM/ECM conflicts.

5. 5

   Module Replacement

   If the fault re-occurs after the harness is verified and the software is updated, remove and replace the Engine Control Module.