seat Workshop Repair Guides

SEAT Workshop Service and Repair Manuals

ABOUT US
Supplementary signals: testing > < Speed signal checking

Leon Mk1

Data bus checking
Data bus checking
Function
Communication between the engine control unit and all data-bus-compatible control units is carried out via a CAN-bus.
Data-bus-compatible control units are connected via two data bus wires twisted together (CAN_High and CAN_Low) and exchange information (messages). Information not available in the data bus will be recognised as a fault by the engine control unit as well as other CAN data bus control units.
The CAN data bus requires a matching resistor of 66Ω to function fault free. This matching resistor is located in the engine control unit.
Test conditions
l  A fault has been recognised by the CAN data bus self-diagnosis.
Special tools and workshop equipment required
t  Test box -V.A.G 1598/31-
t  Hand multimeter -V.A.G 1526 A- or multimeter -V.A.G 1715-
t  Adapter set -V.A.G 1594 C-
t  Current flow diagram
Test sequence
–  Switch off ignition.
–  Unlock the engine control unit connector and pull it off.
–  Connect test box -V.A.G 1598/31- to engine control unit. The engine control unit wiring harness is not connected.
–  Check centralised matching resistor in engine control unit with adaptor cables -V.A.G 1594 C-.
–  Measure resistance between contacts 58+60
   Specification: 60...72 Ω
If the resistance measurement is outside the specified range:
–  Renew engine control unit → Chapter.
If the resistance value is within the specified range:
–  Check wiring to the individual data bus components for open circuit, short to positive and earth using current flow diagram → Current flow diagrams, Electrical fault finding and Fitting locations.
   

Supplementary signals: testing > < Speed signal checking