Information Bus: Testing and Inspection

CAN-Bus, Checking

Vehicles with automatic transmission only

Function
The engine control module communicates with all control modules capable of data bus via a CAN data bus.

The control modules capable of data bus are connected together via two data bus wires (CAN high and CAN low) and exchange information (messages).

Further information:
Self study program No. 186 "The CAN data bus".

Test conditions
A malfunction has been recognized by the CAN data bus On Board Diagnostic.

Special tools and equipment
- Test box VAG 1598/18
- Test box VAG 1598/22
- Hand multimeter VAG 1526 or multimeter VAG 1715
- Adapter set VAG 1594
- Wiring diagram

Test sequence
- Switch ignition off.







- Disconnect connector -arrow- from transmission control module.

NOTE: The transmission control module is located below the rear seat bench.







- Connect test box VAG 1598/18 to transmission control module wiring harness -1- and lock -2-.
- Check CAN data bus wiring with terminal resistors in engine control modules:
- Perform a resistance measurement between test box sockets 3 + 25.
Specification: 55 to 75 Ohms

If the resistance value is outside the specified range:
- Unlock engine control module connector and pull it off.
- Again perform a resistance measurement between test box sockets 3 + 25 of test box 1598/18.

Specification: Infinite Ohm







- Connect test box VAG 1598/22 to control module wiring harness.
- Check CAN data bus wiring between test box sockets for open circuit using wiring diagram:
1598/22 1598/18
Socket 29 and socket 3 and
socket 41 socket 25
Wire resistance: Max. 1.5 Ohm
- Additionally check wires for short to one another.
Specification: Infinite Ohm

If no wiring malfunction is detected:
- Replace engine control module.