display LEXUS SC400 1991 Service Owner's Manual

Check voltage between terminals TP and SG of air conditioner control
assembly connector.
(1) Remove console upper panel.(See page BO±111).
(2) Remove A/C control assembly with connec±
tors still connected.
(3) Turn ignition switch ON.
Change the set temperature to activate the air mix
damper, and measure the voltage between termi-
nals TP and SG of air conditioner control assem-
bly connector each time when the set temperature
is changed.
Set TemperatureVoltage
Max. cool
Max. hot 3.70± 4.27 V
0.88 ± 1.16 V
In addition, as the set temperature increases,
the voltage decreases gradually without inter-
ruption.
Proceed to next circuit inspection shown on
matrix chart (See page AC-36).However,
when Diag. code 31 or 41 is displayed, check and
replace air conditioner control assembly.
Check air mix damper position sensor.
(1) Remove heater unit. (See page AC-125)
(2) Disconnect air mix servomotor assembly
connector.
Measure resistance between terminals S5 and SG of
air mix servomotor assembly connector.
Resistance:4.7~7.2 k

While operating air mix servomotor as in the
procedure on page AC-61, measure resistance
between terminals TP and SG of air mix servo-
motor assembly connector.
Position Resistance
Max. cool
Max. warm 3.76 ~ 5.76 k


0.94 ~ 1.44 k

As the air mix servomotor moves from cool side
to warm side, the resistance decreases gradually
without interruption.
Replace air mix servomotor assembly.
Check for open and short in harness and connector between air conditioner
control assembly and air mix servomotor assembly (See page IN-27).
Repair or replace harness or connector.
Check and replace air conditioner control
assembly.
INSPECTION PROCEDURE
±
AIR CONDITIONING SYSTEM TroubleshootingAC±59
WhereEverybodyKnowsYourName

Diag. Code 32, 42Air Inlet Damper Position Sensor Circuit
CIRCUIT DESCRIPTION
This sensor detects the position of the air inlet
damper and sends the appropriate signals to the
air conditioner control assembly.
The position sensor is built into the air mix servo-
motor assembly.
Code No.Diag. Code Detecting ConditionTrouble area
32Short to ground or power source circuit in air
inlet damper position sensor circuit.
Air inlet damper position sensor.

Harness or connector between air inletser-
vomotor assembly and A/C controlassem-
42
Air inlet damper position sensor value does not
change even if A/C control assembly operates
air inlet servomotor.vomotor assembly and A/C controlassem-
bly

A/C control assembly
DIAGNOSTIC CHART
Check voltage between terminals TP1 and SG
of air conditioner control assembly
connector.
Check air inlet damper position sensor.
Check harness and connector between air
conditioner control assembly and air inlet
servomotor assembly (See page IN±27).
Check and replace air conditioner control
assembly.
Proceed to next circuit inspection
shown on matrix chart (See page
AC-36 ). However, when Diag.
code 32 or 42 is displayed, check
and replace air conditioner control
assembly.
Replace air inlet servomotor
assembly.
Repair or replace harness or
connector.
AC±62±
AIR CONDITIONING SYSTEM Troubleshooting
WhereEverybodyKnowsYourName

Check voltage between terminals TP1 and SG of air conditioner control
assembly connector.
(1) Remove console upper panel.(See page BO-111).
(2) Remove A/C control assembly with connec±
tors still connected.
(3) Turn ignition switch ON.
Press REC/FRS switch to change the air inlet
between fresh and recirculation air, and measure
voltage between terminals TP1 and SG of air
conditioner control assembly when the air inlet
servomotor operates.
In addition, as the air inlet servomotor is moved
from REC side to FRS side, the voltage de-
creases gradually without interruption.
Proceed to next circuit inspection shown on matrix chart
(See page AC-36).However, when Diag. code 32 or 42 is
displayed, check and replace air conditioner control assem-
bly.
Check air inlet damper position sensor.
(1) Remove heater unit. (See page AC-127)
(2) Disconnect air inlet servomotor assembly
connector.
Measure resistance between terminals S5 and SG of
air inlet servomotor assembly connector.
Resistance: 4.7~7.2 k

While operating air inlet servomotor as in the
procedure on page AC-65, measure resistance
between terminals TP1 and SG of air inlet servo-
motor assembly connector.
Resistance:
As the air inlet servomotor moves from REC side
to FRS side, the resistance decreases gradually
without interruption.
Replace air inlet servomotor assembly.
Check for open and short in harness and connector between air conditioner
control assembly and air inlet servomotor assembly (See page IN-27).
Repair or replace harness or connector.
Check and replace air conditioner control assembly.
INSPECTION PROCEDURE
±
AIR CONDITIONING SYSTEM REPAIR INSTRUCTIONSAC±63
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Diag. Code 33, 34 Air Outlet Damper Position Sensor Circuit
CIRCUIT DESCRIPTION
This sensor detects the position of the air outlet
damper and sends the appropriate signals to the
air conditioner control assembly.
The position sensor is built into the air outlet ser-
vomotor assembly.
Code No.Diag. Code Detecting ConditionTrouble area
33Short to ground or power source circuit in air
outlet damper position sensor circuit.
Air outlet damper position sensor.

Harness or connector between air outlet
servomotor assembly and A/C control as-
43
Air outlet damper position sensor value does
not change even if A/C control assembly
operates air outlet servomotor.servomotor assembly and A/C control as-
sembly

A/C control assembly
DIAGNOSTIC CHART
Check voltage between terminals TPM and
SG of air conditioner control assembly
connector.
Check air outlet damper position sensor.
Check harness and connector between air
conditioner control assembly and air outlet
servomotor assembly (See page IN±27).
Check and replace air conditioner control
assembly.
Proceed to next circuit inspection
shown on matrix chart (See page
AC-36 ). However, when Diag.
code 33 or 43 is displayed, check
and replace air conditioner control
assembly.
Replace air outlet servomotor
assembly.
Repair or replace harness or
connector.
AC±66±
AIR CONDITIONING SYSTEM Troubleshooting
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Actuator check.
(1) Set to the actuator check mode(See page AC-30).
(2) Press the FRS switch and change it to step operation.
Press FRS switch and check the
condition of the flow.
The mode changes with the change in the tem-
perature display as shown in the table.
Proceed to next circuit inspection shown on
matrix chart (See page AC-36).
Connect positive
lead to terminal 4 and negative
 lead to terminal 5.
The lever turns smoothly to FACE position.
Remove heater unit.(See page AC-125).
Connect negative  lead to terminal 4 and positive

lead to terminal 5.
The lever moves smoothly to DEF position.
Check air outlet servomotor.
Replace air outlet servomotor.
Check for open and short in harness and connector between air conditioner control
assembly and outlet servomotor, outlet servomotor and battery, outlet servomotor and
body ground.(See page IN-27).
Repair or replace harness or connector.
Check and replace air conditioner control
assembly.
INSPECTION PROCEDURE
±
AIR CONDITIONING SYSTEM TroubleshootingAC±69
WhereEverybodyKnowsYourName

\
\


\

\
\
Temperature Control Switch Circuit
CIRCUIT DESCRIPTION
By turning the temp. control switch, the set temperature of the
A/C can be adjusted in steps of 1
°F (USA) or 0.5 °C (Canada).
Turning the switch fully will set the A/C to MAX. COLD or MAX.
HOT.
The ECU calculates the set temperature from the combination
of Hi (5 V) or Low (0 V) terminals SET 1 ~ 5 of the temp. control
SW and displays the set temperature on the LCD display.
If a malfunction occurs in the temp. control SW circuit, malfunc-
tions such as not being able to set the desired temperature oc-
cur.
DIAGNOSTIC CHART
WIRING DIAGRAM
Check for open and short in harness and
connector between A/C control assembly and
temp. control SW.
Check temp. control switch.
Proceed to next circuit inspection
shown on matrix chart (See page
AC-36 ).
Replace temp. control switch.
Repair or replace harness or
connector.
Check and replace A/C control assembly.
Check voltage between terminal SET 1 ~ 5
and SG of A/C control assembly.
AC±92±
AIR CONDITIONING SYSTEM Troubleshooting
WhereEverybodyKnowsYourName

 
Diag. Code 15\
 \
Open in Front Airbag Sensor Circuit
CIRCUIT DESCRIPTION
The front airbag sensor detects the deceleration force in a frontal collisi\
on and is located in the front fender
on the left and right sides.
For details of the function of each component, see FUNCTION OF COMPONENT\
S on page AB±5.
Diagnostic code 15 is recorded when an open is detected in the front air\
bag sensor circuit.
NOTICE: The front airbag sensor connector is equipped with an electrical connection \
check mechanism
for the purpose of detecting an open in the front airbag sensor (See page AB±7). This mechanism is
constructed so that when the terminals of the front airbag sensor have been connect\
ed (when the connec-
tor housing lock is in the locked condition), the connection detection \
pin on the wire harness side connects
with the terminals for diagnosis use on the sensor side. If the connector is\
not properly connected, the diag-
nosis system may detect only a malfunction code, even though the airbag syste\
m is functioning normally.
When connecting the front airbag sensor connector, make sure it is connected properly. If diagnostic code
15 is displayed after the front airbag sensor connector has been connect\
ed, check again that it is properly
connected.
 

Code No.
\
 
\

\
Diagnosis
 




15
\
 
\


\

\



Open circuit in +S wire harness or ±S wire harness of front airbag s\
ensor.

Front airbag sensor malfunction.

Malfunction of electrical connection check mechanism of front airbag se\
nsor.

Center airbag sensor assembly malfunction.
AB±68±
SRS AIRBAG Troubleshooting
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Diag. Code 22Airbag Warning Light System Malfunction
CIRCUIT DESCRIPTION
The airbag warning light is located on the combination meter.
When the airbag system is normal, the airbag warning light lights up for\
approx. 6 seconds after the
ignition switch is turned from LOCK position to ACC or ON position, and then turns off automatically.
If there is a malfunction in the airbag system, the airbag warning light\
lights up to inform the driver of
the abnormality.
When terminals Tc and E of the TDCL are connected, the diagnostic code is displayed by t\
he blinking
of the airbag warning light.
The airbag warning light circuit is equipped with an electrical connecti\
on check mechanism which
detects when the connector to the center airbag sensor assembly is not p\
roperly connected.
If the connector to the center airbag sensor assembly is not properly co\
nnected, the airbag warning
light will not light up.
Diagnostic code 22 is recorded when a malfunction occurs in the airbag w\
arning light system.
If an OPEN malfunction occurs in the airbag warning light system, the ai\
rbag warning light does not
light up, so that until the malfunction is repaired, the diagnostic code\
s (including code 22) cannot be
confirmed.
Code No.Diagnosis
22
Open circuit in airbag warning light system.22
Center airbag sensor assembly malfunction.
AB±74±
SRS AIRBAG Troubleshooting
WhereEverybodyKnowsYourName

YES
Is diagnostic code 31 output again?
NO
1
Replace center airbag sensor assembly. Using simulation method, reproduce
malfunction symptoms
(See page
IN±20).
Diag. Code 31Center Airbag Sensor Assembly Malfunction
CIRCUIT DESCRIPTION
The center airbag sensor assembly consists of a center airbag sensor, safing sensors, ignition control
and drive circuit, diagnosis circuit, etc.
It receives signals from the airbag sensors, judges whether or not the a\
irbag must be activated, and
diagnoses system malfunction.
Diagnostic code 31 is recorded when occurrence of a malfunction in the center airba\
g sensor assembly
is detected.
Code No.Diagnosis
31 Center airbag sensor assembly malfunction.
DIAGNOSTIC CHART
HINT: When a malfunction code other than code 31 is displayed at the same tim\
e, first repair the
malfunction indicated by the malfunction code other than code 31.
AB±80
±
SRS AIRBAG Troubleshooting
WhereEverybodyKnowsYourName

1
NG
OK
(1) Turn ignition switch LOCK, and wait at least 20
seconds.
(2) Turn ignition switch ACC or ON, and wait at least 20 seconds.
(3) Repeat operation in step (1) and (2) at least 5 times.
(4) Using SST, connect terminals Tc and E
1 of TDCL.
SST 09843±18020
(5) Check diagnostic code.
Is diagnostic code 31 output again?
Using simulation method, reproduce
malfunction symptoms (See page IN±20).
Clear malfunction code stored in memory
(See page
AB±32).
Replace center airbag sensor assembly.
INSPECTION PROCEDURE
HINT:When a malfunction code other than code 31 is displayed at the same time, fi\
rst repair the malfunction indicated by the malfunction code other than code 31.
±
SRS AIRBAG TroubleshootingAB±81
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