1991 LEXUS SC400 sensor

Diag. Code 31, 41Air Mix Damper Position Sensor Circuit
CIRCUIT DESCRIPTION
This sensor detects the position of the air mix
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
31Short to ground or power source circuit in air
mix damper position sensor circuit.
Air mix damper position sensor

Harness or connector between air mix
servomotor assembly and A/C control
41
Air mix damper position sensor value does
not change even if A/C control assembly
operates air mix servomotor.servomotor assembly and A/C control
assembly.

A/C control assembly
DIAGNOSTIC CHART
Check voltage between terminals TP and
SG of air conditioner control assembly
connector.
Check air mix damper position sensor.
Check harness and connector between air
conditioner control assembly and air mix
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.
code31 or 41 is displayed, check
and replace air conditioner control
assembly.
Replace air mix servomotor
assembly.
Repair or replace harness or
connector.
AC±58±
AIR CONDITIONING SYSTEM Troubleshooting
WhereEverybodyKnowsYourName

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 41Air Mix Servomotor Circuit
CIRCUIT DESCRIPTION
The air mix servomotor is controlled by the A/C control assembly and moves \
the air mix damper to the
desired position.
Code No.Diag. Code Detecting ConditionTrouble area
41
Air mix damper position sensor value does not
change even if A/C control assembly operates
air mix servomotor.
Air mix servomotor.

Air mix damper position sensor.

Harness or connector between A/C controlas-
sembly and A/M servomotor, A/M damperposi-
tion sensor.

A/C control assembly.
DIAGNOSTIC CHART
Actuator check.
Check air mix servomotor.
Check harness and connector between air
conditioner control assembly and air mix
servomotor assembly (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 mix servomotor
assembly.
Repair or replace harness or
connector.
AC±60±
AIR CONDITIONING SYSTEM Troubleshooting
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
WhereEverybodyKnowsYourName

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

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
WhereEverybodyKnowsYourName