Volkswagen Workshop Service and Repair Manuals > Polo Mk3 > Power unit | 3-cylinder diesel engine | Fuel preparation system Diesel injection | Checking additional signals

Checking speed signal

Special tools and workshop equipment required

t	Fault reader -V.A.G 1551-

t	Diagnosis lead -V.A.G 1551/3C-

t	Adapter cable, 121-pin -V.A.G 1598/31-

t	Hand multimeter -V.A.G 1526C-

t	Auxiliary measuring set -V.A.G 1594C-

t	Current flow diagram

Test prerequisite

l	Speedometer OK, check: → Rep. Gr.90

Test procedure

Note

To check the speed signal the vehicle must be driven. To do this a second person is necessary.

WARNING

Secure fault reader to rear seat and operate from this position.

–	Connect fault reader -V.A.G 1551- and select engine electronics control unit with “address word 01”. Engine must be idling. (Connecting fault reader and selecting engine electronics control unit → Chapter.)

Indicated on display:

–	Press buttons 0 and 8 for function “Read measured value block” and confirm entry with Q button.

Rapid data transfer                 HELP

Select function XX

Indicated on display:

–	Press buttons 0, 0 and 6 for “display group number 6” and confirm entry with Q button.

–	Carry out a road test and compare display with speedometer (2nd person required).

Reading measured value block

Input display group number XXX

Specification display zone 1: Approx. vehicle speed.

–	Press the → button.

–	Press buttons 0 and 6 for function “End output” and confirm entry with Q button.

If no speed is indicated:

–	Switch off ignition.

Read measured value block 6          ->

     55 km/h     0  0  0     60.5%     255

–	Connect adapter cable, 121-pin -V.A.G 1598/31- to control unit wiring harness.

–	Connect hand multimeter -V.A.G 1526C- to measure voltage between sockets 4/5 + 20 of adapter cable, 121-pin -V.A.G 1598/31-.

–	Switch on ignition.

–	Lift vehicle at front left.

–	Rotate front wheel and observe voltage display. Specification: between 0 and at least 10 Volt fluctuating

If the display does not fluctuate:

–	Check wiring from engine control unit connector contact 20 to dash panel insert for open/short circuit → Current flow diagrams, Electrical fault finding and Fitting locations.

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