Checking brake light switch F and brake pedal switch F47 — VW

Checking
brake light switch
F
and
brake pedal switch
F47
As the injection system operates with an accelerator sender (potentiometer), which may be defective, the engine is regulated for reasons of safety when the brakes are operated. To do this the control unit requires the brake light switch signal and also the brake pedal switch signal. This means that, if the brake is operated while the accelerator is held constantly depressed, the engine is immediately governed down to idling speed. Incorrectly adjusted switches may lead to unrequired regulating action
Special tools and workshop equipment required
Fault reader
V.A.G 1551
or
vehicle system tester
V.A.G 1552
with diagnosis cable
V.A.G 1551/1
or
V.A.G 1551/3
Test box
V.A.G 1598/31
Hand-held multimeter
V.A.G 1526C
Auxiliary measuring set
V.A.G 1594C
Current flow diagram
Test procedure
Connect
fault reader
V.A.G 1551
and select engine electronics control unit with
“address word 01”
. The ignition must be switched on for this purpose.
Indicated on display:
Rapid data transfer HELP
Select function XX
Press keys
0
and
8
for function
“Read measured value block”
and confirm entry with
Q
key.
Indicated on display:
Read measured value block HELP
Input display group number XXX
Press keys
0
,
0
and
6
for
“Display group number 6”
and confirm entry with
Q
key.
Observe display in display zone 2.
Specification: 0 0 0
Read measured value block 6 ->
0 km/h 0 0 0 000000 255
Operate brake pedal slowly.
Specification: 0 1 1 Both displays must change from 0 to 1 at same time.
Read measured value block 6 ->
0 km/h 0 1 1 000000 255
Middle display =
brake pedal switch
F47
Right display =
brake light switch
F
Release brake pedal slowly into rest position again.
Both displays must change from 1 to 0 again.
Read measured value block 6 ->
0 km/h 0 0 0 0.0% 255
If one or both displays do not change:
Press
→
key.
Press keys
0
and
6
for function
“End data transfer”
and confirm entry with
Q
key.
Switch off ignition.
Pull 4-pin connector from
brake light switch
F
and
brake pedal switch
F47
⇒ Overview of fitting locations, Page
Chapter
.
Connect
hand-held multimeter
V.A.G 1526C
to measure resistance between contacts 1 and 4. Specification: ∞ Ω (no continuity).
Depress the brake pedal. Specification: approx. 0 Ω
Connect
hand-held multimeter
V.A.G 1526C
to measure resistance between contacts 2 and 3. Specification: approx. 0 Ω
Depress the brake pedal. Specification: ∞ Ω (no continuity).
If the specifications are not attained:
Renew
brake light switch
F
and
brake pedal switch
F47
.
If the specifications are attained:
Connect
hand-held multimeter
V.A.G 1526C
to measure resistance between contact 1 and earth. Specification: at least 11.5 V
Switch on ignition.
Connect
hand-held multimeter
V.A.G 1526C
to measure resistance between contact 2 and earth. Specification: at least 11.5 V
If the specifications are not attained:
Check line between 4-pin connector contact 1 and 2 and central electrics using current flow diagram.
Current flow diagrams, Electrical fault finding and Fitting locations
If specification is attained:
Connect
test box
V.A.G 1598/31
to control unit wiring harness.
Note
If necessary, left headlight may have to be released and placed to side to connect
test box
V.A.G 1598/31
Electrical system; Rep. Gr. 94; Lights, bulbs, switches - exterior
.
Check lines between
test box
V.A.G 1598/31
and 4-pin connector for open circuit using current flow diagram. Contact 3+socket 65 Contact 4+socket 32 Line resistance: Max. 1.5 Ω
Additionally check lines for short circuit to one another.
Additionally check lines for short circuit to battery positive or earth.