Computers and Control Systems: Diagnostic Trouble Code Tests and Associated Procedures
P1855
SAE VAG Description
P1855 18263 Data-Bus Powertrain Software version Contr.
Terminal resistance for CAN-Bus
Terminal resistance for CAN-Bus, checking See: Component Tests and General Diagnostics/Terminal Resistance For CAN-Bus, Checking.
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Computers and Control Systems: Component Tests and General Diagnostics
With Manufacturer's Scan Tool
CAN-Bus, checking
1 - Engine Control Module (ECM)
2 - ABS control module
3 - Transmission Control Module (TCM)
- Only vehicles with automatic transmission
4 - Airbag control module
5 - Instrument cluster
6 - CAN-Bus
Function
The Engine Control Module (ECM) (item -1-) communicates with the ABS control module (item - 2-), the Transmission Control Module (item
-3-), the airbag control module (item -4-) and the instrument cluster (item -5-) via a CAN-Bus (item -6-).
At least two control modules capable of CAN-Bus are connected by two wires (CAN-High and CAN-Low, twisted together) and exchange
information (messages). Missing information on the CAN-Bus will be recognized as a malfunction by the ECM as well as by other CAN-Bus
control modules.
All control modules have 120 W terminal resistors which make sure that the CAN-Bus can function without fault.
Special tools and equipment
- Multimeter (Fluke 83 or equivalent)
- VW 1594 adapter set
- Wiring diagram
- VAG1598/21 Test box
Test conditions
- Malfunction has been recognized by CAN-Bus OBD
- ABS control module coded to CAN-Bus operation
- Check CAN-Bus wiring using wiring diagram.