1998 AUDI A3 brake

24-143


Brake light switch and brake pedal switch,
checking

Special tools and equipment

VAG1526A
VAG1527B
VAG1594A
VAG1598/31
VAS5051 with VAG5051/1
- or
VAG1551 with VAG1551/3A
Pa
ge 38 of 51 Electronic En
gine Power Control
(EPC
) (E-Gas
), checkin
g
11/21/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.FU06.24.4

24-144

Note:
For safety reasons, the instruction from the
accelerator pedal sensor (potentiometer) to the
ECM to open the throttle valve is suppressed
when brake is being operated. This requires the
brake light switch signal and also the brake pedal
switch signal in the control module. If brake pedal
is operated with accelerator pedal constantly
depressed, engine is immediately regulated
down to idle speed. A faulty switch can lead to
undesired regulation.

Test sequence

- Connect VAS5051 tester or VAG1551 scan tool
and select control module for engine electronics
using "address word" 01 Page 01
-10
. Ignition
must remain switched on.
Rapid data transfer
HELP
Select function XX

When indicated on display
- Press buttons -0- and -8- to select "Read Measuring Value Block" and
press -Q- button to confirm input.
Read measurin
g value block
Q
Enter displa
y group number XXX

When indicated on display
- Press buttons -0-, -6- and -6- to select "display group number 066" and
press -Q- button to confirm input.
Pa
ge 39 of 51 Electronic En
gine Power Control
(EPC
) (E-Gas
), checkin
g
11/21/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.FU06.24.4

24-145

Read Measuring Value Block 66
1
2
3
4

Indicated on display
- Check brake light/brake pedal switch in display field 2.

Display fields

1 2 3 4
Display group 066: Signals to Engine Control Module (ECM)
Display xxx km/h
XXXX xxx km/h XXXX
Indicated ACTUAL speed
Switch positions SPECIFIED speed Switch positions
Functional range
XX00
XX11
Specified value
XX00
(with brake pedal not operated)

XX11
(with brake pedal operated)
Note
Value:X = no significance.
Switch points slightly offset
Pa
ge 40 of 51 Electronic En
gine Power Control
(EPC
) (E-Gas
), checkin
g
11/21/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.FU06.24.4

24-146
If indications do not resemble description:

Check switch

- Remove driver-side storage compartment.

Repair Manual, Body Interior, Repair Group
68; Instrument panel; Driver
-side storage
compartment, removing


- Disconnect harness connector at brake light
switch and brake pedal switch.

If specified values are not obtained: - Connect multimeter between terminal 1 and 2 for resistance
measurement.

Specification: (no continuity)
- Depress accelerator pedal.

Specification: approx. 0
- Connect multimeter between terminal 3 and 4 for resistance
measurement.

Specification: approx. 0
- Depress accelerator pedal.

Specification: (no continuity)
Pa
ge 41 of 51 Electronic En
gine Power Control
(EPC
) (E-Gas
), checkin
g
11/21/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.FU06.24.4

- Replace brake light switch / brake pedal switch.
Pa
ge 42 of 51 Electronic En
gine Power Control
(EPC
) (E-Gas
), checkin
g
11/21/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.FU06.24.4