1991 LEXUS SC400 sensor

1. CONTINUITY CHECK (OPEN CIRCUIT CHECK)(1) Disconnect the connectors at both ECU and sensor sides.
(2) Measure the resistance between the applicable terminalsof the connectors.
Resistance: 1
or less
HINT:
w Measure the resistance while lightly shaking the wire
harness vertically and horizontally.
w When tester probes are inserted into a connector, insert
the probes from the back. For waterproof connectors in
which the probes cannot be inserted from the back, be
careful not to bend the terminals when inserting the
tester probes.
2. RESISTANCE CHECK (SHORT CIRCUIT CHECK) (1) Disconnect the connectors at both ends.
(2) Measure the resistance between the applicable terminalsof the connectors and body ground. Be sure to carry out
this check on the connectors on both ends.
Resistance: 1 M
or higher
HINT: Measure the resistance while lightly shaking the wire
harness vertically and horizontally.
3. VISUAL CHECK AND CONTACT PRESSURE CHECK (a) Disconnect the connectors at both ends.
(b) Check for rust or foreign material, etc. on the terminalsof the connectors.
(c) Check crimped portions for looseness or damage and check if the terminals are secured in the lock position.
HINT: The terminals should not come out when pulled lightly.
(d) Prepare a test male terminal and insert it in the female
terminal, then pull it out.
HINT: When the test terminal is pulled out more easily than
others, there may be poor contact in that section.
IN±28
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INTRODUCTION How to Troubleshoot ECU Controlled Systems
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CONTROL FUNCTIONS
Interior Room Temperature Control System
(a) The desired temperature is set using the TEMP switch.
(b) From the input signals (room temperature sensor, ambient temperature sensor, evaporator temperaturesensor and solar sensor) and the temperature setting, the air conditioner con\
trol ECU determines the air
flow volume and outputs signals to the air mix servomotor.
(c) When it receives signals from the ECU, the air mix servomotor opens or close\
s the air mix damper to change the air flow temperature. When the temperature reaches the specified te\
mperature, it is detected
by the air mix damper position sensor and the ECU stops the servomotor.
HINT: If the desired temperature setting is 65 °F, the ECU forcedly sets the air mix damper to the Max Cool posi-
tion. If it is set at 85 °F, the ECU forcedly sets the air mix damper to the Max Hot position.
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AIR CONDITIONING SYSTEM DescriptionAC±9
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Blower Fan Speed Control System
(When AUTO Switch is ON)
(a) The desired temperature is set using the TEMP switch.
(b) From the input signals (room temperature sensor, ambient temperature sensor and solar sensor) and thetemperature setting, the air conditioner control ECU determines the air flow volume\
and outputs signals
to the power transistor.
(c) When it receives signals from the ECU, the power transistor increases or red\
uces the blower motor speed to control the air flow volume.
(When AUTO Switch is OFF)
The ECU turns the power transistor increasing or reducing the blower mot\
or speed fixing the air flow volume
in accordance with the position of the Manual switch. AC±10
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AIR CONDITIONING SYSTEM Description
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Air Flow Mode Control System
(When the AUTO Switch is ON)
(a) The desired temperature is set using the TEMP switch.
(b) From the input signals (room temperature sensor, ambient temperature sensor and solar sensor) and thetemperature setting, the air conditioner control ECU determines the air flow mode a\
nd outputs signals to
the mode servomotor and max cool servomotor.
(c) When it receives signals from the ECU, the servomotors open or close each of\
the dampers to change the air flow mode.
(When the AUTO Switch is OFF)
The ECU fixes the air flow mode in accordance with the Manual switch pos\
ition.
(When the Engine is Cold)
If the Mode is set on B/L or FOOT, the ECU forcedly changes the air vent to DEF if cold signals are input from
the water temperature sensor.
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AIR CONDITIONING SYSTEM DescriptionAC±11
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Air Inlet Control System
(When the AUTO Switch is ON)
(a) The desired temperature is set using the TEMP switch.
(b) From the input signals (room temperature sensor, ambient temperature sensor and solar sensor) and thetemperature setting, the air conditioner control ECU determines the air \
inlet and outputs signals to the air
inlet servomotor assembly.
(c) When it receives signals from the ECU, the air inlet servomotor opens or clo\
ses the damper to change the air inlet. When the air inlet is changed to the desired setting, it is detected by the air inlet damper p\
osition
sensor and the ECU stops the servomotor.
HINT: If the Mode switch is set on DEF, the ECU forcedly changes the air inlet to FRS.
(When the AUTO Switch is OFF)
The ECU fixes the air inlet according to the position of the manual swit\
ch. AC±12
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AIR CONDITIONING SYSTEM Description
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HOW TO PROCEED WITH TROUBLESHOOTING
Perform troubleshooting in accordance with the procedure on the following page.\
[1] CUSTOMER PROBLEM ANALYSIS Using the customer problem analysis check sheet for reference, ask the c\
ustomer in as much detail as
possible about the problem. A subjective complaint such as ºpoor air conditio\
ner efficiencyº is also consid-
ered in the air conditioner complaints.
Therefore, in ºCustomer Problem Analysisº and ºProblem Symptom Confirmationº\
, check carefully to deter-
mine whether the level of performance is the actual (normal) level or whet\
her it is abnormal. Then perform
troubleshoot accordingly.
[2] CHECK AND CLEAR THE DIAGNOSTIC CODES (PRECHECK) First check the diagnostic codes to see if there are any malfunction cod\
es stored in memory. If there are
malfunction codes, make a note of them, then clear them and proceed to [3] problem \
Symptom Confirma-
tionº.
[3] PROBLEM SYMPTOM CONFIRMATION, [4] SYMPTOM SIMULATION Confirm the problem symptoms. If the problem does not reappear, be sure to simulate the problem by main-
ly checking the circuits indicated by the diagnostic code in step [2], u\
sing ºProblem Simulation Methodº.
[5] DIAGNOSTIC CODE CHECK
Check the diagnostic codes. Check for problems with the sensors or the w\
ire harness.
[6] DIAGNOSTIC CODE CHART If a malfunction code is confirmed in the diagnostic code check, proceed t\
o the check procedure indicated
by the matrix chart for each diagnostic code.
[7] MATRIX CHART OF PROBLEM SYMPTOMS
If the normal code is confirmed in the diagnostic code check, perform in\
spection in accordance with the
inspection order in the matrix chart of problem symptoms.
[8] CIRCUIT INSPECTION Proceed with diagnosis of each circuit in accordance with the inspection order c\
ofirmed in [6] and [7]. Deter-
mine whether the cause of the problem is in the sensor, actuators, wire harness and connectors, or the
ECU.
[9] ACTUATOR CHECK Check actuators for proper operation. Instructions for this diagnosis ar\
e given in the flow chart for each
circuit.
[10] REPAIRS After the cause of the problem is located, perform repairs by following the i\
nspection and replacement pro-
cedures in this manual.
[11] CONFIRMATION TEST
After completing repairs, confirm not only that the malfunction is elimi\
nated, but also perform diagnostic
code check and actuator check, etc. again to make sure the entire air condit\
ioning system is operating cor-
rectly.
AC±22
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AIR CONDITIONING SYSTEM REPAIR INSTRUCTIONS
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DIAGNOSIS SYSTEM
Warning for A/C compressor lock
If compressor lock occurs during air conditioner operation, the
( A/C ) switch indicator on the air conditioner control assembly
starts blinking to warn the driver.
When this occurs, check for compressor lock (code 22) using diag-
nostic code check then proceed to inspect the circuit or the com-
ponent.
Compressor lock sensor circuit page AC±54.
LIST OF OPERATION METHODS
By operating each of the air conditioner control switches as shown in the \
diagram below, it is possible to enter
the diagnosis check mode. AC±26
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AIR CONDITIONING SYSTEM Troubleshooting
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INDICATOR
1. Turn the ignition switch on while pressing the ari conditioner control
switch and REC swich
simultaneously.
2. Check that all the indicators light up and go off at 1 second intervals 4 times in succession.
3. Check that the buzzer sounds when the indicators light up in 2.
HINT:
wAfter the indicator check is ended, the diagnostic code
check begins automatically.
w Press the OFF switch when desiring to cancel the check
mode.
DIAGNOSTIC CODE CHECK (SENSOR
CHECK)
1. Perform an indicator check. After the indicator check is completed, the system enters the diagnostic code check
mode automatically.
2. Read the code displayed on the panel. Refer to the list of
codes on page AC±28 when reading the codes. (Codes are
output at the temperature display.)
If the slower display ped is desired, press the FRS
switch and change it to stepped operation. Each time the
FRS
switch is pressed, the display changes by 1 step.
HINT:
w If the buzzer sounds when a code is being read, it means
the trouble indicated by that code continues to occur.
w If the buzzer does not sound when a code is being read,
it means the trouble indicated by that code occurred ear-
lier (such as poor connector contacts, etc.)
CLEARING DIAGNOSTIC CODES
1. Pull out the DOME fuse in Relay Block No. 2 for 10 sec. or
longer to clear the memory of diagnostic codes.
2. After reinserting the fuse, check that the normal code is output.
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AIR CONDITIONING SYSTEM TroubleshootingAC±27
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