1996 AUDI A4 AEB ATW Engines Charge Air System With Turbocharger Workshop Manual

21-59
charge air pressure regulation Diagnostic Trouble Codes (DTC) Diagnostic Trouble
Code (DTC) Charge air pressure
Possible causes
Charge air pressure
too low
Measured value below
1.450 bar or 1450 mbar
Wastegate bypass regulator valve -N75- faultyWire to wastegate bypass regulator valve -N75- faultyCharge air pressure regulator valve in turbocharger is stuck in
open position Leak between turbocharger and intake manifoldMechanical recirculation valve faultyTurbocharger malfunctioning
Charge air pressure
too high
1)
Measured value above
1.700 bar or 1700 mbar
Vacuum diaphragm for charge air pressure regulator valve
faulty Hoses to vacuum diaphragm for charge air pressure regulation
valve (via wastegate bypass regulator valve -N75-) leaky Charge air pressure regulator valve in turbocharger is stuck in
closed position
1) If charge air pressure is too high, the fuel supply is shutoff to protect the engine. The engine misfires at high engine
speeds.
Pa
ge 17 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
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pair&id=AUDI.B5.GE02.21.3

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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

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Note:
The wastegate bypass regulator valve -N75- and
wire connections are monitored by the Engine
Control Module (ECM).

- Connect VAS5051 tester or VAG1551 scan tool
and select control module for engine electronics
using "address word 01". Engine must run at idle
for this:

Repair Manual, 1.8 Liter 4-Cyl. 5V Turbo Fuel
Injection & Ignition, Repair Group 01
- Check DTC memory of Engine Control Module
(ECM):

Repair Manual, 1.8 Liter 4-Cyl. 5V Turbo Fuel
Injection & Ignition, Repair Group 01 If a malfunction relating to the wastegate bypass
regulator valve -N75- is indicated:

- Disconnect hoses from valve; harness connector
remains connected.

-
Attach assisting hose to one connection of
Pa
ge 19 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

valve.
Pa
ge 20 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

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- Initiate output Diagnostic Test Mode (DTM) and
activate the wastegate bypass regulator valve -
N75-.

Repair Manual, 1.8 Liter 4-Cyl. 5V Turbo Fuel
Injection & Ignition, Repair Group 01 Output Diagnostic Test Mode Waste
gate B
ypass Re
gulator Valve -N75

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 wastegate bypass regulator valve -N75-.
- Disconnect harness connector at valve.

- Connect multimeter at valve for resistance measurement.

Specified value: 25-35
Pa
ge 21 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

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If specified value is not obtained:

- Replace wastegate bypass regulator valve -N75-
.
If the specified value is met:

Checking voltage supply

If LED does not light:
Electrical Wiring Diagrams, Troubleshooting & Component Locations - Connect VAG1527B voltage tester as follows:Harness connector
terminal
Measure to
1 Engine Ground (GND)
- Operate starter briefly.

LED must light.
- Check wire connection from terminal 1 to Fuel Pump (FP) relay via
fuse for open circuit:
- Repair open circuit if necessary.
Pa
ge 22 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

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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:

Checking activation

Repair Manual, 1.8 Liter 4-Cyl. 5V Turbo Fuel Injection & Ignition,
Repair Group 01
If LED does not blink or if it remains constantly lit:
Repair Manual, 1.8 Liter 4-Cyl. 5V Turbo Fuel Injection & Ignition,
Repair Group 24 - Connect VAG1527B voltage tester to harness connector terminals 1
(B+) and 2.
- Initiate output Diagnostic Test Mode (DTM) and activate the wastegate
bypass regulator valve -N75-.
LED must blink.
- Connect VAG1598/31 test box at wiring harness to ECM, do not
connect ECM:
Pa
ge 23 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

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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
2 104
- Repair open circuit or short circuit if necessary.
- Replace Engine Control Module (ECM):
Pa
ge 24 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