AUDI A4 1998 B5 / 1.G AWM Engine Charge Air Syst

21-10


- Connect T piece and measuring hose of turbocharger tester VAG 1397
A to intake manifold (front).
- Route measuring hose under rear edge of hood and into passenger
compartment via right hand window.

- Switch on turbocharger tester and set measuring range selector switch
to position -I- (absolute pressure).
- Connect measuring hose to connection -I-.
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21-11

Note:

Hose connections must be completely airtight,
otherwise measurements will not be correct.
Ensure that measuring hose is not pinched at
hood or side window.
Pressing memory key M on turbocharger tester
will store the last measured value until memory
key M is pressed again or tester is switched off.
The decimal point in the display flashes to
indicate that the value is being stored.
If the battery voltage of the turbocharger tester
drops below the minimum level, an arrow will
appear at the top left of the display.
Before checking, drive vehicle quickly for at
least 3 km (choose a safe route that does not
include stopping).
A second mechanic is required to note readings
with the vehicle moving.
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21-12

Read measured value block 115
1
2
3
4

Note:
The charge pressure level is measured with turbocharger tester VAG
1397/A. The vehicle diagnostic, measuring and information system VAS
5051 or the VAG 1551 Scan Tool is used to check whether the charge
pressure is being registered by the control module. - Read measured value block Display group 115, engine idling.
- Accelerate vehicle from 2000 rpm at wide open throttle in third gear,
and observe rev counter.
- At approx. 2500 rpm press print key on VAS 5051 or PRINT key on
VAG 1551 and at same time press recall button -M- on VAG 1397 A.

Specified value on VAG 1397 A: 1.700 to 1.800 bar
Read measured value block 115
1
2
3
4

If specified value not attained table, Page 21
-13

Specified value on VAG 1551 or on VAS 5051 in display zone 4: 1700
to 1800 mbar
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21-13
Charge air pressure control malfunctions Malfunction
Possible causes
Charge air pressure below
specified value
Wastegate Bypass Regulator valve -N75- faulty checking, Page 21
-33
Hose connection to Wastegate Bypass Regulator valve -N75- faulty Connection
diagram, Page 21
-3
Wastegate bypass regulator valve in turbocharger stuck openLeak between exhaust turbocharger and intake hose Effects, Page 21
-14
Mechanical air recirculation valve faulty checking, Page 21
-24
Recirculating valve for turbocharger -N249- faulty checking, Page 21
-26
Exhaust turbocharger faulty replacing, Page 21
-51
Charge air pressure above
specified value
1)
Vacuum unit for wastegate bypass regulator valve faulty Replacing exhaust
turbocharger, Page 21
-51

Hose connection to vacuum unit for charge air pressure limiter (above -N75-) leaks
Connection diagram, Page 21
-3
When in closed position wastegate bypass regulator valve in exhaust turbocharger
sticks replacing exhaust turbocharger, Page 21
-51

1) If the charge air pressure is too high the fuel supply will be interrupted in order to protect the engine. This results in misfiring
at high engine speeds.
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21-14

Effects of leaks in intake or exhaust
system


Leak downstream of mass air flow sensor

Effect: Loss of power

Possible malfunction sources:

1 - Connection hoses between mass air flow
sensor and exhaust turbocharger

2 - Connection hose for crankcase vent

3 - Connection hose to mechanical air
recirculation valve
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11/21/2002 htt
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21-15

Leak downstream of exhaust turbocharger

Effect: Charge pressure too low

Possible malfunction sources:

1 - Connection hoses and line between exhaust
turbocharger and charge air cooler

2 - Hose between charge air cooler and intake
line

3 - Charge air cooler

4 - Seal of Charge Air Pressure sensor -G31- (in
charge air cooler)

5 - Sealing between throttle valve control
module and intake line

6 - Sealing between intake line and cylinder
head

Effects of leaks on exhaust side
Effect: Charge air pressure too low, possible
exhaust smell, soot traces in engine
compartment
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Possible malfunction sources:

1 - Exhaust turbocharger /exhaust manifold
connection

2 - Exhaust manifold/cylinder head connection
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11/21/2002 htt
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pair&id=AUDI.B5.GE06.21.1