Audi Workshop Service and Repair Manuals > A4 Mk1 > Power unit | Motronic injection and ignition system (6 cyl. turbo) | Mixture preparation system, electronic inj.,Gas | Checking auxiliary signals

Motronic injection and ignition system (6 cyl. turbo)

Checking auxiliary signals

Checking vehicle speed signal

Notes:

◆ The vehicle speed signal is generated by the road speed sender -G68 (on the gearbox) and is processed in instrument cluster (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.

‒ Start the engine.
‒ Connect up vehicle diagnostic, testing and information system VAS 5051 or fault reader V.A.G 1551 and select engine electronics control unit with "Address word" 01 .
‒ Select "Read measured value block" (function 08) and display group 5.

→ Display:

Read measured value block 5 ⇒

1 2 3 4

Important!
The V.A.G 1551 must be operated by a second person.

‒ Take vehicle for a test drive and check whether the vehicle speed appears in display zone 3.
‒ If the road speed does not appear, raise the vehicle (preferably using a lifting platform) until the front left wheel is clear of the ground.

‒ → Connect V.A.G 1598/31 test box to wiring harness leading to engine control unit; the engine control unit should not be connected .
‒ Connect diode test lamp between socket 3 (positive) and socket 54 (road speed signal).
‒ Switch on the ignition and turn the front left wheel by hand.
‒ The diode test lamp should flash (very brief flashes).
‒ If the diode test lamp does not flash, check for open circuit or short circuit to positive/earth in wiring between dash panel insert and contact 54 on connector of engine control unit.

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