AUDI A4 1998 B5 / 1.G AC System On Board Diagnostic Workshop Manual

01-1


A/C system, On Board
Diagnostic (OBD)

Function
The A/C control head -E87- receives input
information from various electrical and electronic
components (sensors).
This information is processed by the control head
in accordance with specified values and then
provides corresponding output signals that
control electrical components (actuators).
The control head is controlled by an internal
microprocessor with On Board Diagnostic (OBD)
capability. If faults or open circuits occur on
applicable components, Diagnostic Trouble
Codes (DTC) are stored in DTC memory. Stored
faults are identified using either VAG1551 Scan
Tool (ST) or VAG1552 Scan Tool (ST). Tables
containing all DTCs and corresponding repair
information guide technicians through the OBD
process.
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01-2

Notes:

This Repair Manual describes On Board
Diagnostic (OBD) with VAG1551 Scan Tool
(ST). OBD procedures can also be performed
with VAG1552 Scan Tool (ST) (VAG1552 Scan
Tool is not equipped with a printer).
Scan Tool VAG1551 or 1552 must be used in in
operating mode -1- (Rapid data transfer).
Operating mode -2- (Flash code output) is not
provided for A/C and Heating OBD.
Always check DTC memory and perform
necessary repairs before erasing DTC memory.
DTC output is possible only if ignition is on or
engine is running and engine speed is less than
3000 rpm (if engine speed is higher, output is
possible only for a limited time or is terminated).
If a fault exists for a certain time it is stored as a
static fault.
If a static fault is no longer present after a
certain time, it is stored as a sporadic fault and
the reference "SP" appears on the upper right
of the VAG1551 display/print-out.
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Before replacing a suspected malfunctioning
component, check all related wiring,
connections, harness connectors and Ground
(GND) connections according to the appropriate
wiring diagram.
Output Diagnostic Test Mode (DTM), Basic
Setting, A/C control head identification and
coding functions are also possible.
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01-3

Notes:

A/C system component locations: engine
compartment page 87
-96
.

A/C system component locations: passenger
compartment page 87
-106
.

If a the display of a newly installed A/C control
head -E87- flashes after switching the ignition
on (for approximately 2 minutes), code the
control head page 01
-57
and execute basic
setting page 01
-52
.

If a replacement control head is not coded after
installation or if an unrecognized code was
entered, code "00042" (4-cyl. gasoline engine
USA) is stored.
Control of A/C compressor, flap motors and fan
motors etc. is not possible when executing
Output Diagnostic Test Mode (DTM), function
03 and basic setting, function 04. A/C control is
possible in all other functions.
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01-4

Heating and A/C system changes, 1997


On Board Diagnostic changes

New A/C control head -E87- with specific
coding for m.y. 1997, 4-cyl. and 6-cyl. engines.

Notes:
Before performing On Board Diagnostic of A/C
system, ensure A/C control head -E87- is coded
correctly (according to engine application).
A/C control heads beginning with Part No. 8L0
820 043 should only be installed in m.y. 1997
vehicles.
A/C control heads beginning with Part No. 8D0
820 043 must only be installed in vehicles
through m.y. 1996.

CAUTION!
Part numbers are for reference only.
Always check with your Parts Dept. for the
latest information.
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01-5

Notes:

For m.y. 1997, changes that affect monitoring of
the A/C system by A/C control head -E87- were
made.
Monitored components, locations pages 87
-
101
and Page 87
-113
.

Additional technical data and notes page 01
-
1 .

If a replacement A/C control head is not coded
after installation or if an unrecognized code was
entered, code "04142" (Audi A4 -4cyl. -USA) is
stored.
The A/C control head is no longer connected to
terminal 30 (vehicle electronics). The last input
setting (into the A/C control head) is stored
when the ignition is switched off and retained
when the ignition is switched on.
The duration of time when ignition is off is
calculated by the A/C control head. When
ignition is switched on, the previous "standing
time" is calculated by monitoring a time signal
from the instrument cluster. If more than 4
hours pass since ignition was switched off, the
actual measured values of the outside
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temperature sensor are used as instantaneous
outside and engine temperature inputs for A/C
system control. If "standing time" is shorter than
4 hours, the actual measured values of the
outside temperature sensor are suppressed
and system output temperature control is
calculated by the A/C control head. The
"standing time" period is monitored and used
for this calculation. (Heat radiating from the
engine and radiator leads affects the measured
value of the temperature sensor).
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01-6
The following components previously monitored
by OBD and triggered by A/C control head -E87-
are deleted:

Refrigerant low pressure switch -F73-.
Refrigerant high pressure switch -F118- (low
and high pressure switch functions integrated
into A/C pressure switch, -F29-).
Fresh air/recirculating flap two-way valve -
N63-.
The following new components are monitored by
OBD and provide input signals to -E87-:
A/C pressure switch -F129-.
Sender for outlet temperature, center -G191-.
Sender for outlet temperature, floor outlet -
G192-.
The following components monitored by OBD or
triggered by -E87- are revised:
The heater/air conditioner assembly with all
servo motors.
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The fresh air blower and control module.
Following components that provide input signals
to the A/C control head -E87- are revised:
Instrument cluster
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01-7

A/C system changes

Revised heating/air conditioner assembly with
flap motors page 87
-174
.

The air flow flap motor now activates the fresh
air/recirculating air flap as well.
The two way valve for the circulating/fresh air
door, the vacuum unit and the vacuum reservoir
are deleted.

A/C refrigerant circuit changes
New service valve connection on low pressure
side.
Service valve connection for high pressure side
installed in high pressure line in plenum panel
(deleted at condenser).
A/C pressure switch -F129- replaces pressure
switches -F73- and -F118-.
New version "Zexel" compressor and high
pressure line (4-cyl. engines only).
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