Lexus SC300 / Lexus SC400. Manual — part 25
Diag. Code 31, 41
Air 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 Condition
Trouble area
31
Short 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
).
Check and replace air conditioner control
assembly.
Proceed to next circuit inspection
shown on matrix chart (See page
). 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
Check voltage between terminals TP and SG of air conditioner control
assembly connector.
(1)
Remove console upper panel.
(See page
(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 Temperature
Voltage
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
).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
(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
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
).
Repair or replace harness or connector.
Check and replace air conditioner control
assembly.
INSPECTION PROCEDURE
–
AIR CONDITIONING SYSTEM
Troubleshooting
AC–59
Diag. Code 41
Air 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 Condition
Trouble 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
Check and replace air conditioner control
assembly.
Proceed to next circuit inspection
show on matrix chart (See page
Replace air mix servomotor
assembly.
Repair or replace harness or
connector.
AC–60
–
AIR CONDITIONING SYSTEM
Troubleshooting
Actuator check.
(1)
Warm up the engine.
(2)
Set to the actuator check mode (See page
).
(3)
Press the FRS switch and change it to
step operation.
Press the FRS switch and check the
operation of the air mix damper and the condition
of the blower.
Proceed to next circuit inspection shown on
matrix chart (See page
Check air mix servomotor.
Remove heater unit.
Connect positive
lead to terminal 4 and negative
lead to terminal 5.
The lever turns smoothly to cool side.
Connect negative
lead to terminal 4 and positive
lead to terminal 5.
The lever turns smoothly to hot side.
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
Repair or replace harness or connector.
Check and replace air conditioner control
assembly.
INSPECTION PROCEDURE
–
AIR CONDITIONING SYSTEM
Troubleshooting
AC–61
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