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Testing air conditioner compressor shut-off > < Testing crash signal

A4 Mk1

Motronic injection and ignition system (4-cyl.)
Testing auxiliary signals
Testing road speed signal

Notes:

  • ◆ The road speed signal is generated by the road speed sender -G68 (on the gearbox) and is processed in the dash panel insert.
  • ◆ The processed signal goes to contact 54 on the engine control unit and is used for idling speed stabilisation and for the damping of load change jolts when changing gear.
  • ‒ Connect vehicle diagnostic, testing and information system VAS 5051 (or fault reader V.A.G 1551) and select engine electronics control unit by entering address word "01" ( .)
    When doing this the engine must be idling.
 
→ Indicated on display:
Rapid data transfer    HELP
Select function XX
  • ‒ Press keys 0 and 8 for the function "Read measured value block" and confirm entry with Q key.
 
→ Indicated on display:
Read measured value block    
Enter display group number XXX
  • ‒ Press keys 0, 0 and 5 to select Display Group 5 and confirm entry with Q key.
 
→ Indicated on display:
Read measured value block 5    ⇒
    1    2    3    4
  • ‒ Take vehicle for a test drive.
Important:
Secure fault reader to rear seat and operate from this location. When doing this, always observe the relevant safety precautions => Page 24-1.
  • ‒ Check display value for vehicle speed.

Display zones

1

2

3

4

Display Group 5: Vehicle speed

Display

xxxx rpm

xxx.xx %

xxx km/h

Text

Indicates

Actual engine speed
(in steps of 40 rpm)

Engine load

Vehicle speed

Operating status

Range

min.: 750 rpm
max.: 6800 rpm

min.: 0 %
max.: 120.00 %

min.: 0 km/h
max.: 250 km/h

Idling / part throttle / full throttle / overrun cut-off / acceleration enrichment

Specification

xxxx rpm

xxx.xx %

current
speed

---

Note

The display should show the approximate current speed (compare with speedometer
reading).
If readout does not match specification, test wiring

If the vehicle speed is not displayed:

  • ‒ Connect test box V.A.G 1598/31 to wiring harness for engine control unit. Do not connect to the engine control unit itself.
    => Page 24-10.

Test the following wiring connections for open circuits and short to positive or earth.

Test box V.A.G 1598/31, socket

Dash panel insert, contact

54

=> Current flow diagrams, Electrical fault finding and Fitting locations binder
  • Resistance in wiring: max. 1.5 ω
  • ‒ Rectify any open/short circuit as necessary.

If no wiring fault is detected:

  • ‒ Establish which electrical "consumers" (e.g. radio, automatic gearbox, air conditioner etc.) are using the speed signal, disconnect them one by one from the dash panel insert, then keep repeating the test until the cause of the problem has been identified.

Testing air conditioner compressor shut-off > < Testing crash signal