ESP 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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01-42

Output Diagnostic Test Mode (DTM)
(function 03)


Function
Output DTM allows functional checking of A/C
control head actuated components (DTM
components). Actuators receive output signals
generated by the control head via VAG1551
Scan Tool (ST) in sequence. Function is
confirmed in accordance with specified
responses.
The following components are tested in
sequence using Output DTM:

1 - A/C Clutch -N25-

2 - Fresh Air Blower -V2-

3 - Coolant Fan -V7-

4 - Fresh Air/Recirculating Flap Two-Way Valve
-N63-1)

5 - Temperature Regulator Flap Motor -V68-

6 - Central Air Flap Motor -V70-
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01-45

Notes:

If a DTM component fails to respond as
specified, perform all corrective actions, checks
and tests recommended in output DTM table
page 01
-46
.

A/C system component locations: engine
compartment page 87
-96
(note specific
model year information).

A/C system component locations: passenger
compartment page 87
-106
(note specific
model year information).

Output DTM can be ended by pressing the -C-
button.
After ending output DTM, check DTC memory
page 01
-18
.

If the readout "function unknown or cannot be
carried out at the moment" appears in the
display at the start of output DTM, e.g. when
engine not running, press button and once
again select "function 03 Output Diagnosis Test
Mode (DTM)" (DTM component "A/C Clutch
N25" is no longer actuated for this test).
Pa
ge 63 of 91 A/C s
ystem, On Board Dia
gnostic
(OBD
)
11/21/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.HA01.01.1