check AUDI A6 1998 C5 / 2.G AEB ATW Engines Charge Air System With Turbocharger Workshop Manual

21-46


Charge air system with
turbocharger (engine code
ATW)

Checking mechanical recirculation valve

Notes:

The mechanical recirculation valve is located in
front of the turbocharger. It is opened by
vacuum via the recirculating valve for
turbocharger -N249- during deceleration, idle
and part throttle. This produces a reduction of
the charge air pressure in front of the throttle
valve which keeps the turbocharger spinning at
a higher RPM.
Check the recirculation valve in case of reduced
performance or part throttle hesitation.

Special tools and equipment

VAG1390
Pa
ge 1 of 42 Char
ge air s
ystem with turbochar
ger
(en
gine code ATW
)
11/18/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.GE02.21.3

21-48


Recirculating valve for turbocharger -
N249-, checking

Special tools and equipment

VAG1526A
VAG1527B
VAG1594A
VAG1598/31
VAS5051 with VAG5051/1
- or
VAG1551 with VAG1551/3A
Pa
ge 3 of 42 Char
ge air s
ystem with turbochar
ger
(en
gine code ATW
)
11/18/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.GE02.21.3

21-50

- Initiate output Diagnostic Test Mode (DTM) and
activate the recirculating valve for turbocharger -
N249-:

Repair Manual, 1.8 Liter 4-Cyl. 5V Turbo Fuel
Injection & Ignition, Repair Group 01 Output Diagnostic Test Mode Recirc. valve for turbochar
ger -N249

Indicated on display
If valve does not click:
If valve does not open and close properly:
Checking internal resistance Valve must click...
...and must open and close (can be tested by blowing into assisting
hose).
- Check internal resistance of valve.
- Replace recirculating valve for turbocharger -N249-.
- Disconnect harness connector at valve.

- Connect multimeter at valve for resistance measurement.

Specified value: 27-30
Pa
ge 5 of 42 Char
ge air s
ystem with turbochar
ger
(en
gine code ATW
)
11/18/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.GE02.21.3

21-51
If the specified value is attained:

- Check voltage supply

Checking voltage supply

Note:
Voltage is supplied to the recirculation valve via
the Fuel Pump (FP) relay.

Test requirement

Fuse for recirculation valve OK

- Disconnect harness connector at valve.

- Connect VAG1527B voltage tester as follows:Harness connector
terminal
Measure to
1 Engine Ground (GND)
- Operate starter briefly.

LED must light.
Pa
ge 7 of 42 Char
ge air s
ystem with turbochar
ger
(en
gine code ATW
)
11/18/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.GE02.21.3

21-52
If LED does not light:

- Check wire connection from terminal 1 to Fuel
Pump (FP) relay via fuse for an open circuit":

Electrical Wiring Diagrams, Troubleshooting &
Component Locations
- Repair open circuit if necessary.
If wire connection is OK:

- Check Fuel Pump (FP) relay:

Repair Manual, 1.8 Liter 4-Cyl. 5V Turbo Fuel
Injection & Ignition, Repair Group 24 If LED lights:

- Check activation:

Checking activation

- Connect VAG1527B voltage tester to connector terminals 1 (B+) and 2.
-
Initiate output Diagnostic Test Mode (DTM) and activate the
Pa
ge 8 of 42 Char
ge air s
ystem with turbochar
ger
(en
gine code ATW
)
11/18/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.GE02.21.3

21-53
If LED does not blink or if it remains constantly
lit:

- Connect VAG1598/31 test box at wiring harness
to ECM, do not connect ECM:

Repair Manual, 1.8 Liter 4-Cyl. 5V Turbo Fuel
Injection & Ignition, Repair Group 24

If wire connection is OK:
Repair Manual, 1.8 Liter 4-Cyl. 5V Turbo Fuel Injection & Ignition,
Repair Group 24 - Check the following wire connection for open circuit and short circuit to
Ground (GND) and B+: Harness connector
terminal
VAG1598/31 test box
socket
2 105
- Repair open circuit or short circuit if necessary.
- Replace Engine Control Module (ECM):
Pa
ge 10 of 42 Char
ge air s
ystem with turbochar
ger
(en
gine code ATW
)
11/18/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.GE02.21.3

21-54

Turbocharger and charge air pressure
regulator valve, checking


Special tools and equipment

VAG1397A

VAS5051 with VAG5051/1
orVAG1551 with VAG1551/3A
Pa
ge 11 of 42 Char
ge air s
ystem with turbochar
ger
(en
gine code ATW
)
11/18/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.GE02.21.3

21-55

Test requirements

All hoses and wires have been checked for
proper seating and seal.
DTC memory checked

Repair Manual, 1.8 Liter 4-Cyl. 5V Turbo Fuel
Injection & Ignition, Repair Group 01

Output Diagnostic Test Mode (DTM)
performed

Repair Manual, 1.8 Liter 4-Cyl. 5V Turbo Fuel
Injection & Ignition, Repair Group 01

Vehicle tester VAS 5051 or VAG 1551
connected.

Test sequence

WARNING!

To reduce the risk of accident or injury while
carrying out tests and measurements during
a road test, observe safety precautions
Page 21
-40
.
Pa
ge 12 of 42 Char
ge air s
ystem with turbochar
ger
(en
gine code ATW
)
11/18/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.GE02.21.3

21-58

Note:
The height of the charge air pressure should be
determined using the VAG1397/A turbocharger
test tool, the VAS5051 tester or the VAG1551
Scan Tool is used to determine whether the
charge air pressure is also being recognized in
the control module.

Specification on VAG1397A: 1.450-1.700 bar
Read Measuring Value Block 115 3000 RPM
42%
1770 mbar
1770 mbar

If the specification is exceeded or not met:
Repair Manual, 1.8 Liter 4-Cyl. 5V Turbo Fuel Injection & Ignition,
Repair Group 01
Specified value on VAS 5051 or VAG 1551 Display field 4: 1450-1700
mbar
- Check DTC memory of Engine Control Module (ECM):
Pa
ge 16 of 42 Char
ge air s
ystem with turbochar
ger
(en
gine code ATW
)
11/18/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.GE02.21.3

21-60


Wastegate bypass regulator valve -N75-,
checking

Special tools and equipment

VAG1526A
VAG1527B
VAG1594A
VAG1598/31
VAS5051 with VAG5051/1
- or
VAG1551 with VAG1551/3A
Pa
ge 18 of 42 Char
ge air s
ystem with turbochar
ger
(en
gine code ATW
)
11/18/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.GE02.21.3