AUDI A8 1999 D2 / 1.G AHA Engine Auxiliary Signals Checking Workshop Manual

24-164


Auxiliary signals, checking

Signal from A/C compressor, checking


Required special tools and test equipment

VAG1551 or VAG1552 Scan Tool (ST) with
VAG1551/3 adapter cable
VAG1598/22 test box
Multimeter US1119 (Fluke 83 or equivalent)
VW1594 connector test kit
Wiring diagrams

Test conditions
A/C functions OK
A/C is switched off
Vehicle at room temperature-above 15 C
(59 F)

No malfunctions stored in Diagnostic Trouble
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Code (DTC) memory page 01
-16
.
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Checking

- Connect VAG1551 or VAG1552 scan tool and
press buttons -0- and -1- to insert "Engine
Electronics" address word 01 (with engine
running at idle) page 01
-8 .
Rapid data transfer
HELP
Select function XX

Indicated on display
- Press buttons -0- and -8- to select "Read Measuring Value Block"
function 08, and press -Q- button to confirm input.
Read Measurin
g Value Block
HELP
Input displa
y group number XXX

Indicated on display
- Press buttons -0-, -5- and -0- to input display group number 50 (050),
and press -Q- button to confirm input.
Read Measuring Value Block 50 1 2 3 4

Indicated on display (1-4 = display fields)
- Switch on A/C (lowest temperature and highest fan position).
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- Compare display with specified values for A/C
(in display field 4).

Display fields

1 2 3 4
Display group 50: Signals to Engine Control Module (ECM)
Display xxxx RPM xxxx RPM A/C-LOW
A/C-HIGH Compr. ON
Compr. OFF
Indicates Actual engine
speed
(in 10 RPM steps) Specified engine
speed
(in 10 RPM steps) IAC boost A/C compressor status
Range 0 - 2550 RPM --- --- ---
Specified
value 620 - 740 RPM
(all-wheel drive)
or
740 - 860 RPM
(front-wheel drive) 680 RPM
(all-wheel drive)
or
800 RPM
(front-wheel drive) A/C-LOW
(all-wheel drive)
or
A/C-HIGH
(front-wheel
drive) Compressor on: Comp. ON
Compressor off: Comp. OFF

--- --- --- If not as specified page 24
-167
,
Continuation
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Notes:

The A/C compressor is switched off during
acceleration when the car is stationary or at
slow speed.
At wide open throttle the A/C compressor is
switched off by the Transmission Control
Module (TCM) (via the kick down switch).
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24-167

Continuation
If the displayed values are NOT OK:

- Connect VAG1598/22 test box to ECM harness
connector page 01
-67
.

- Check wiring for open circuit, short circuit to B+
or short circuit to Ground between ECM/test box
terminal 8 and either A/C control head -E87- or
Transmission Control Module (TCM).

Electrical Wiring Diagrams, Troubleshooting &
Component Locations binder If the wiring is OK:

- Check function of A/C control head -E87-.

Repair Manual, Heating & Air Conditioning,
Repair Group 01


- Carry out electrical testing of automatic
transmission.
Repair Manual, 5 Spd. Automatic
Transmission 01V, Repair Group 01
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- Check readiness code page 01
-70
. If
Diagnostic Trouble Code (DTC) memory has
been erased, or ECM was disconnected,
generate new readiness code page 01
-73
.
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24-168

Vehicle speed signal, checking


Required special tools and test equipment

VAG1551 or VAG1552 Scan Tool (ST) with
VAG1551/3 adapter cable
Multimeter US1119 (Fluke 83 or equivalent)
VW1594 connector test kit
Wiring diagrams

Test conditions
Vehicle Speed Sensor (VSS) OK; checking:

Repair Manual, Electrical Equipment, Repair
Group 90


Notes:

To check Vehicle Speed Sensor -G68-, the
vehicle must be driven. A second technician is
required to operate the scan tool during the
road test.
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Read safety precautions for test driving vehicles
while using test equipment page 24
-9 .

The speed signal is generated by the vehicle
speed sensor (at the transmission), and
processed at the speedometer/odometer in the
instrument cluster.
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Test procedure

- Connect VAG1551 or VAG1552 scan tool and
press buttons -0- and -1- to insert "Engine
Electronics" address word 01 (with engine
running at idle) page 01
-8 .
Rapid data transfer
HELP
Select function XX

Indicated on display
- Press buttons -0- and -8- to select "Read Measuring Value Block"
function 08, and press -Q- button to confirm input.
Read Measurin
g Value Block
HELP
Input displa
y group number XXX

Indicated on display
- Press buttons -0-, -0- and -5- to input display group number 5 (005),
and press -Q- button to confirm input.
Read Measuring Value Block 5 1 2 3 4

Indicated on display (1-4 = display fields)
- Road test and compare indicated vehicle speed with value in display
field 3 (2nd technician required, Safety precautions page 24
-9 ).
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