Scania Truck ALM Alarm System: ALM404 Fault in the CAN Communication – Troubleshooting Guide

This guide provides step-by-step instructions on how to identify and resolve the ALM404 CAN communication fault in Scania trucks, specifically related to the Chassis Management System (CMS).

Related Contents:

The ALM404 fault occurs when a Controller Area Network (CAN) message expected from the coordinator fails to arrive at the CMS control unit.

Possible Causes

1. Open circuit in the voltage supply to the CMS control unit.
2. CMS control unit is not connected to the orange CAN bus.
3. Coordinator is not connected to the orange CAN bus.
4. Physical or electrical fault in the orange CAN bus.

Symptoms

• Reduced or lost functionality in systems that rely on the CMS control unit.

Recommended Actions

1. Read Fault Codes:
   • Attempt to retrieve fault codes from the CMS control unit using diagnostic tools.
2. Check Voltage Supply:
   • Inspect the power supply and terminal 15 (ignition voltage) to the CMS control unit.
   • Verify correct voltage levels and continuity.
3. Verify CAN Bus Connections:
   • Check the physical connection of the CMS control unit to the orange CAN bus.
   • Ensure the coordinator is properly connected to the same CAN bus.
4. Inspect the Orange CAN Bus:
   • Check the integrity and continuity of the orange CAN bus wiring.
   • Inspect for signs of damage, corrosion, or loose connectors.
5. Check Termination Resistors:
   • Confirm that termination resistors are correctly installed at both ends of the CAN bus.
   • Measure voltage and load on the CAN line as per Scania specifications.
6. Use Diagnostic Support:
   • Refer to the Help > Communication Fault section in your Scania diagnostic software for more detailed analysis and support procedures.

For more information about Scania truck,please refer to:Scania Trouble Repair.