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Testing databus (CAN bus) > < Testing the speed signal

Octavia Mk1

Testing engine speed signal
Testing engine speed signal
Special tools and workshop equipment required
t  Vehicle system tester -V.A.G 1552- with cable -V.A.G 1551/3, 3A, 3B oder 3C-
t  Test box -V.A.G 1598/22- or -V.A.G 1598/31-
The speed signal is necessary for rev counter and air conditioning. For the automatic gearbox, it is required for calculating the gear-change points. The signal conditioning which is generated by the engine speed sender -G28-, is however not readable and therefore it is processed first in the engine control unit.
The speed signal can be determined as follows:
Dash panel insert
–  Connect vehicle system tester -V.A.G 1552- and activate the function “read measured value block” → Chapter.
–  Read measured value block, display group 001, engine at idling speed → Chapter.
–  Briefly apply full throttle.
   
Specified value in display field 1: The current engine speed must be displayed (uniform in the whole speed range). This speed display must correspond with the display at the rev counter.
If the specified value is not reached:
–  Connect test box to wiring loom to engine control unit → Chapter.
For the test box -V.A.G 1598/22-
–  Check the wiring from rev counter to contact 6 of the test box for open circuit → Current flow diagrams and Fitting locations.
For the test box -V.A.G 1598/31-
–  Check the wiring from rev counter to contact 27 of the test box for open circuit → Current flow diagrams and Fitting locations.
Continued for all vehicles
Air Conditioning
The signal is monitored by the self-diagnosis (fault memory, read measured value block) of the air conditioning system.
Signal test → Heating and Air conditioning system → Rep. Gr.01.
Specified value:
The current engine speed must be displayed in the emasured value block.
If the nominal value is not reached by all “units” of the speed signal, the following faults are possible:
t  Line interruption, or short circuit between engine control unit and plug connection in wiring loom → Current flow diagrams and Fitting locations.
t  Short circuit between plug connection in wiring loom and “unit”.
t  Engine control unit - J248- defective.
If the nominal value is not reached by at least one “unit” of the speed signal, the following faults are possible:
t  Line interruption between plug connection in wiring loom and “unit”.
t  “Unit” defective.
  
Reading measured value block   1   ->
900 rpm    4.6 mg/s   1.680 V    87.3 °C

Testing databus (CAN bus) > < Testing the speed signal