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Vehicle Speed Signal (VSS), checking
Notes:
The vehicle speed signal is generated by the
Vehicle Speed Sensor (VSS) -G68 (on the
transmission) and is processed in the
instrument cluster.
The processed signal goes to terminal 54 on
the engine control module and is used for Idle
Air Control (IAC) and for the damping of load
change jolts when changing gear.
- Start engine.
- Connect vehicle diagnostic, testing and
information system VAS 5051 or VAG1551 scan
tool and select engine electronics control
module by entering address word "01" Page 01
-9 .
- Select "Read measured value block" (function
08) and Display Group 5. Read Measuring Value Block 5
1
2
3
4
Indicated on display:
Warning!
During a road test in an airbag equipped vehicle, VAG1551 must
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Data exchange between Engine/ABS/
Transmission control module, checking
Notes:
The data exchange between the various control
modules is carried out via a bus system.
The term "Bus" refers to a system for
transmitting and distributing data.
The wires which connect the control modules
and convey the data between them are called
data wires.
Data is transmitted via data wires in serial, i.e.
in a specific order to the connected control
modules.
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Read measuring value block 125
1
2
3
4
When indicated on display:
- Check indications in display fields 1 through 4.
CAN capable control modules connected to the Engine Control Module
(ECM) are indicated:
No indication (display field empty): Control module not CAN-
capable
Indication 1: CAN capable control module is connected to databus
Indication 0: CAN capable control module is not connected to
databus (e.g. in case of malfunction)
Read measuring value block 125
ABS 1
Combi 1
Example:
Note:
Display group 125 indicates all systems that communicate with the Engine
Control Module (ECM) via the CAN-bus. (In this example, the ABS control
module and the instrument cluster). If these systems are not installed, the
display fields in display group 125 that are intended for them will be
empty. Display field 1 will indicate "Transmission 1" and display field 4 will
indicate "A/C 1" if these systems are communicated with the Engine
Control Module (ECM) via the CAN-bus.
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