1995 AUDI A4 AFC Engine Auxiliary Input Signals Checking Workshop Manual

24-88


Auxiliary input signals,
checking

Rear window defroster signal, checking


Requirement

Engine Control Module (ECM) coding OK
page 01
-247
.

Checking

- Using VAG 1551 scan tool, select "Read
Measuring Value Block" function 08, display
group 004, display field 4 page 01
-249
.
Read measuring value block 4 1 2 3 4

Indicated on display, note value in display field 4
CAUTION!
Do not use the shift inputs (identified by an X) during the RPM
increase check.
If display value is OK: Specified value: 0XX_XX
- Switch ON rear window defroster.
Specified value: 1XX_XX
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-
Press button.- Select "End Output" function 06.
- Press -Q- button to confirm input.
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If display value does not change:

- Switch ignition OFF and connect VAG 1598/19
test box to ECM harness connector page 01
-
255
.

- Connect VAG 1527B voltage tester between
VAG 1598/19 test box socket C14 and Ground
(GND).

- Switch ignition ON.

- Switch ON rear window defroster.

Voltage tester must light up
If voltage tester does not light up:

If wiring is OK:
If rear window defroster is OK: - Check wiring for continuity between C14 and rear window defroster
using wiring diagram.
- Check rear window defroster using wiring diagram.
- Replace ECM page 01
-265
.
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24-90

A/C compressor shut-off signal,
checking


Note:
The A/C compressor is switched off during
acceleration by the Engine Control Module
(ECM) and at wide open throttle by the
Transmission Control Module (TCM) via the
kickdown switch.
A/C compressor shut-off is bi-directional ("in"and
"out").

IN: Shortly before switching the A/C
compressor on, voltage is applied to the ECM
which causes the Idle Air Control (IAC) valve to
open a little more to adjust to the higher load.
OUT: When accelerating from a standstill
position and at lower speed, the A/C
compressor is shut off for approx. 12 seconds
via control by the ECM. If the accelerator pedal
is released early enough, the duration is
reduced to a minimal 3 seconds.

Checking requirements
A/C function OK

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No malfunctions stored in DTC memory
Vehicle at room temperature; above 15 C
(59 F)
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24-91

Checking

- Start engine and let idle.

- Switch A/C on, push "AUTO" button, set
temperature to "LO" and blower speed to "HI".

A/C compressor symbol must light up and
A/C must run.

- Using VAG 1551 scan tool, select "Basic
Setting" function 04, display group 004 page 01
-150
.

A/C compressor must stop (visual check)
If the A/C compressor does not shut off:

- Switch A/C off (press "minus" button for fresh air
blower in A/C control head repeatedly, until all
indicators are off).

Continue to let engine run in idle.

- Using VAG 1551 scan tool, select "Read
Measuring Value Block" function 08, display
group 004.
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Read measuring value block 4 1 2 3 4

Indicated on display; note value in display field 4
CAUTION!
Do not use the shift inputs (identified by an X) during the RPM
increase check.
- Switch on A/C as described.
Specified value: X1X_XX
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24-92
If the specified values are obtained:

-
Press button.
- Select "End Output" function 06.

- Press -Q- button to confirm input.
If display value changes:

- The following display is possible: "A/C system
not switched on as described."
If the display value does not change, even
though the A/C system was switched on as
described:

If wiring is OK:
Repair Manual, Heating & Air Conditioning, Repair Group 01; connect VAG 1551 scan tool and select "Check DTC Memory" function 02

Repair Manual, 5 Spd. Automatic Transmission 01V, Repair Group 01;
connect VAG 1551 scan tool and select "Check DTC Memory" function 02
- Check wiring for continuity between connector terminal C11 and ECM
or TCM using wiring diagram.
- Check A/C system or automatic transmission:
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