1998 AUDI A4 AFC Engine On Board Diagnostic Multiport Fuel Injection Workshop Manual

01-78

Output on GST and/or on
VAG 1551 scan tool Possible malfunction cause

Malfunction repair
P0402 / 16786
Exhaust Gas Recirculation
Flow Excessive Detected Vacuum line incorrectly connected
and/or hose connections transposed

- Check EGR system vacuum hose
according to vacuum plan page 24
-111


Malfunction cause found: Yes
No

- Erase DTC memory, test drive and after
test drive, check DTC memory again DTC
memory
MIL Status:
MIL lights up after 2 Trips EGR vacuum regulator solenoid
valve -N18- stuck in open position

- Check EGR vacuum regulator solenoid
valve -N18- page 24
-67


Malfunction cause found: Yes
No

- Erase DTC memory, test drive and after
test drive, check DTC memory again DTC
memory

EGR valve leaks or is stuck in
open position

- Check mechanical EGR valve page 24
-
70

For troubleshooting Display
group 017
Malfunction cause found: Yes


- Erase DTC memory, test drive and after
test drive, check DTC memory again
Notes:
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The malfunction "16786" (mech. valve continuously open) is set if after a cold start (-12 C to 30 C (10 to 86 F) coolant
temperature) the EGR temperature is greater than 50 C (122 F) at a coolant temperature of 35 C (95 F).
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01-79

Output on GST and/or on
VAG 1551 scan tool Possible malfunction cause

Malfunction repair
P0422 / 16806
Main Catalyst Efficiency
Below Threshold (Bank 1) Are other malfunctions stored in the DTC
memory?

No

Yes

- First correct these malfunctions
according to Diagnostic Trouble Code
(DTC) table.
MIL Status:
MIL lights up after 2 Trips Malfunction cause found: Yes
No

- Erase DTC memory, test drive and
after test drive, check DTC memory
again

Bank 1 Three Way Catalytic Converter
(TWC) chemically or thermally aged or
mechanically destroyed

- Replace Three Way Catalytic
Converter (TWC) Bank 1
For troubleshooting
Display groups 035, 036,
044
Malfunction cause found: Yes


- Erase DTC memory, test drive and
after test drive, check DTC memory
again
Note:

With the help of the Oxygen Sensor Probe in front of and behind the Three Way Catalytic Converter (TWC), the rate of
Three Way Catalytic Converter (TWC) deterioration is determined using the Three Way Catalytic Converter (TWC) oxygen
storage capability.
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play?action=Goto&t
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01-80

Output on GST and/or on
VAG 1551 scan tool Possible malfunction cause

Malfunction repair
P0432 / 16816
Main Catalyst Efficiency
Below Threshold (Bank 2) Are other malfunctions stored in the DTC
memory?

No

Yes

- First repair these malfunctions
according to Diagnostic Trouble Code
(DTC) table.
MIL Status:
MIL lights up after 2 Trips Malfunction cause found: Yes
No

- Erase DTC memory, test drive and
after test drive, check DTC memory
again

Bank 2 Three Way Catalytic Converter
(TWC) chemically or thermally aged or
mechanically destroyed

- Replace Bank 2 Three Way
Catalytic Converter (TWC)
For troubleshooting
Display groups 035, 036,
044
Malfunction cause found: Yes


- Erase DTC memory, test drive and
after test drive, check DTC memory
again
Note:

With the help of the Oxygen Sensor Probe in front of and behind the Three Way Catalytic Converter (TWC), the rate of
Three Way Catalytic Converter (TWC) deterioration is determined using the Three Way Catalytic Converter (TWC) oxygen
storage capability.
Pa
ge 108 of 366 On Board Dia
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(OBD
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port Fuel In
jection
(MFI
)
11/22/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.FU01.01.1

01-81

Output on GST and/or on
VAG 1551 scan tool Possible malfunction cause

Malfunction repair
P0440 / 16824
Evaporative Emission
Control System Malfunction Evaporative emissions system hoses
kinked or pinched

- Check hoses for correct fit

Malfunction cause found: Yes
No

- Erase DTC memory, test drive and
after test drive, check DTC memory
again
MIL Status:
MIL lights up after 2 Trips Leak in the EVAP system between
Intake manifold and EVAP canister
purge regulator valve -N80- or
EVAP canister purge regulator valve -
N80- and sensor for EVAP canister -
G172- or
Sensor for EVAP canister -G172- and
EVAP canister
- Check EVAP system for leaks

Malfunction cause found: Yes
No

- Erase DTC memory, test drive and
after test drive, check DTC memory
again
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01-82


EVAP canister purge regulator
valve -N80- sticks mechanically

- Check solenoid valve for Evaporative
Emission (EVAP) canister purge -N80- page 24
-58


Malfunction cause found: Yes
No
Continued next page

- Erase DTC memory, test drive and after test
drive, check DTC memory again
For troubleshooting
Display group 030
Sensor for EVAP canister -G172-
(differential pressure sensor) faulty

- Check Sensor for EVAP canister -G172-
(differential pressure sensor) page 24
-61


Malfunction cause found: Yes


- Erase DTC memory, test drive and after test
drive, check DTC memory again
Note:

With the help of the Sensor for EVAP canister -G172- (differential pressure sensor)the pressure is measured between the
Evaporative Emissions (EVAP) canister and solenoid valve for Evaporative Emission (EVAP) canister purge -N80- with
valve closed and open. If the difference in the two pressures is less than 4 mbar to 23 mbar (depending on air pressure),
the malfunction is set.
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(MFI
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play?action=Goto&t
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pair&id=AUDI.B5.FU01.01.1

01-83

Output on GST and/or on
VAG 1551 scan tool Possible malfunction cause

Malfunction repair
P0452 / 16836
Evaporative Emission
Control System Pressure
Sensor Low Input Harness connector on sensor for EVAP
canister -G172- (differential pressure sensor)
loose or corroded due to moisture in the
harness connector

- Check harness connector for tight fit
and contact corrosion, if necessary
reconnect and/or clean

Malfunction cause found: Yes
No

- Erase DTC memory, test drive and
after test drive, check DTC memory
again
MIL Status:
MIL lights up immediately Wiring connection to sensor for EVAP
canister -G172- (differential pressure sensor)
faulty, or sensor -G172- faulty

- Check sensor for EVAP canister -
G172- (differential pressure sensor)
page 24
-61


Malfunction cause found: Yes
No

- Erase DTC memory, test drive and
after test drive, check DTC memory
again
For troubleshooting
Display group 030
Engine Control Module (ECM) -J192- faulty

- Replace and code engine control
module page 01
-265
erase DTC
memory and test drive check DTC
memory
Note:
The malfunction "P0542 / 16836" is set as soon after engine start as the differential pressure sensor signal is less than 0.1 V
Pa
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gnostic
(OBD
) - Multi
port Fuel In
jection
(MFI
)
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p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
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pair&id=AUDI.B5.FU01.01.1

for longer than 2 sec. with a evaporative emissions valve duty cycle greater than 91% (100% = closed).
Pa
ge 112 of 366 On Board Dia
gnostic
(OBD
) - Multi
port Fuel In
jection
(MFI
)
11/22/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.FU01.01.1