LEXUS SC400 1991 Service Repair Manual

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 42Air Inlet Servomotor Circuit
CIRCUIT DESCRIPTION
The air inlet servomotor is controlled by the air conditioner control assem\
bly and moves the air inlet
damper to the desired position.
Code No.Diag. Code Detecting ConditionTrouble area
42
Air inlet damper position sensor value does
not change even if A/C control assembly oper-
ated air inlet servomotor
Air inlet damper position sensor.

Harness or connector between air inlet ser-
vomotor assembly and A/C control assem-
bly.

A/C control assembly
DIAGNOSTIC CHART
Actuator check.
Check air inlet servomotor.
Check harness and connector between air
conditioner control assembly and air inlet ser-
vomotor 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 ).
Replace air inlet servomotor
assembly.
Repair or replace harness or
connector.
AC±64±
AIR CONDITIONING SYSTEM Troubleshooting
WhereEverybodyKnowsYourName

Actuator check.
Proceed to next circuit inspection shown on
matrix chart (See page AC-36).
Check air inlet servomotor.
Remove cooling unit.
Connect positive
lead to terminal 6 and negative 
lead to terminal 2.
The lever moves smoothly to REC position.
Connect negative  lead to terminal 6 and positive

lead to terminal 2.
The lever moves smoothly to FRS position.
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.
(1) Remove glove box to see and check the air
inlet damper operation
(2) Set to the actuator check mode (See page AC±30.
(3) Press the FRS switch and check it to step operation.
Press the FRS switch and change it to step opera-
tion.
INSPECTION PROCEDURE
±
AIR CONDITIONING SYSTEM TroubleshootingAC±65
WhereEverybodyKnowsYourName

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
WhereEverybodyKnowsYourName

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

While operating air outlet servomotor as in the
procedure on page AC-69, measure resistance
between terminals TP1 and SG of air outlet servo-
motor assembly connector.
Resistance:
As the air inlet servomotor moves from DEF side
to FACE side, the resistance decreases gradually
without interruption.
Replace air outlet servomotor assembly.
Check for open and short in harness and connector between air conditioner
control assembly and air outlet 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±67
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Diag. Code 43Air Outlet Servomotor Circuit
CIRCUIT DESCRIPTION
Code No.Diag. Code Detecting ConditionTrouble area
43Air outlet damper position sensor value does not
change even if A/C control assembly operated air
outlet servomotor.
Air outlet servomotor.

Air outlet damper position sensor.

Harness or connector between A/C control
assembly air outlet servomotor, air outlet
damper position sensor.

A/C control assembly
DIAGNOSTIC CHART
Actuator check.
Check air outlet servomotor.
Check harness and connector between air
conditioner control assembly and air outlet
servomotor, air outlet servomotor and bat-
tery, air outlet servomotor and body ground.
(See page IN-27).
Check and replace air conditioner control
assembly.
Proceed to next circuit inspection
show on matrix chart (See page
AC-36 ).
Replace air outlet servomotor .
Repair or replace harness or
connector.
AC±68±
AIR CONDITIONING SYSTEM Troubleshooting
WhereEverybodyKnowsYourName

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

IG Power Source Circuit
CIRCUIT DESCRIPTION
This is the power source for the air conditioner control assembly (contains\
the A/C control assembly)
and servomotor, ect.
DIAGNOSTIC CHART
WIRING DIAGRAM
Check voltage between terminals IG+ and E
of air conditioner control assembly
connector.
Check continuity between terminal E of air
conditioner control assembly and
body ground.
Check HTR fuse.
Check harness and repair and connector be-
tween air conditioner control assembly and
battery
Proceed to next circuit inspection
shown on matrix chart (See page
AC-36).
Check for short in all the harness
and components connected to
the HTR fuse (See attached wir -
ing diagram).
Repair or replace harness or
connector.
AC±70±
AIR CONDITIONING SYSTEM Troubleshooting
WhereEverybodyKnowsYourName

Check voltage between terminals IG+ and E of air conditioner control
assembly connector.
(1) Remove console upper panel.(See pageBO-111 ).
(2) Remove A/C control assembly with connec±
tors still connected.
(3) Turn ignition switch ON.
Measure voltage between terminals IG+ and E of air
conditioner control assembly.
Voltage: 10 ±14 V
Proceed to next circuit inspection shown on matrix
chart (See page AC-36).
Check continuity between terminals E of air conditioner control assem-
bly and body ground.
Measure resistance between terminals E of air condi-
tioner control assembly and body ground.
Resistance:1  or less
Repair or replace harness or connector.
Remove HTR fuse from J/B No. 1.
Check continuity of HTR fuse
Continuity
Check HTR fuse.
Check for short in all the harness and
components connected to the HTR fuse
See attached wiring diagram).
Check and repair harness and connector between air conditioner control \
assembly and battery.
INSPECTION PROCEDURE
±
AIR CONDITIONING SYSTEM TroubleshootingAC±71
WhereEverybodyKnowsYourName