ECU LEXUS SC400 1991 Service Owner's Manual

(a) Continuity Check with Ground
(1) Disconnect connectors (A) and (C) and measure the resistance between terminals 1 and 2 of connector(A) and body ground.
In the case of Fig. 6,
Between terminal 1 of connector (A) and body ground ±> Continuity
Between terminal 2 of connector (A) and body ground ±> No continuit\
y (open)
Therefore, it is found out that there is a short circuit between terminal 1 of con\
nector (A) and terminal 1 of
connector (C).
(2) Disconnect connector (B) and measure the resistance between terminal 1 of connec\
tor (A) and bodyground, and terminal 1 of connector (B) and body ground.
Between terminal 1 of connector (A) and body ground ±> No continuit\
y (open)
Between terminal 1 of connector (B) and body ground ±> Continuity
Therefore, it is found out that there is a short circuit between terminal 1 of con\
nector (B) and terminal 1 of
connector (C).
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INTRODUCTION How to Troubleshoot ECU Controlled SystemsIN±31
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Check and Replace ECU
First check the ECU ground circuit. If it is faulty, repair it. If it is nor-
mal, the ECU could be faulty, so replace the ECU with a known
good one and check if the symptoms appear.
(1) Measure the resistance between the ECU ground terminal and the body ground.
Resistance: 1
or less
(2) Disconnect the ECU connector, check the ground terminals on the ECU side and the wire harness side for bend and
check the contact pressure.
IN±32
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INTRODUCTION How to Troubleshoot ECU Controlled Systems
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GENERAL DESCRIPTION
REFRIGERATION SYSTEM
Prevention of Refrigerant Release and
Excessive Quantities
Refrigerant (CFCs) for automobile air conditioners is be-
lieved to cause harm by depleting the ozone layer which
helps to protect us from the ultraviolet rays of the sun.
Therefore, it is necessary to prevent release of refrigerant to
the atmosphere and to use minimum amount when servicing
the air conditioner.
1. USE RECOVERY MACHINE TO RECOVER REFRIGERANT
When discharging refrigerant from the system as follows, use
a recovery machine to recover the refrigerant.
wBefore replacing parts on the refrigerant line.
w When moisture or air gets in the refrigerant line.
w When excess refrigerant is charged.
NOTICE:
w When handling the recovery machine, always follow
the directions given in the instruction manual.
w After recovery, the amount of compr essor oil
removed must be measured and the same amount
added to the system.
2. USE CHARGING HOSES WITH STOP VALVE WHEN INSTALLING MANIFOLD GAUGE SET
To prevent release of refrigerant, using charging hoses with
a stop valve when installing the manifold gauge set to the ser-
vice valves on the refrigerant line.
3. TIGHTEN CONNECTING PARTS SECURELY Follow the notices about tightening connecting parts in step
6 on page AC±4.
4. PROPERLY EVACUATE AIR FROM REFRIGERANT SYSTEM
To prevent release and wasteful use of refrigerant, evacuate
air with care from refrigeration system as follows:
wDo not evacuate before recovering refrigerant in
system.
w Do not perform repeat evacuation of system.
AC±2
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AIR CONDITIONING SYSTEM General Description
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Handling Precautions for Gas±Cylinder
Type Gas Leak Tester
1. BEFORE USING TESTER MAKE SURE THAT THEREARE NO FLAMMABLE SUBSTANCES NEARBY
2. BE CAREFUL NOT TO INHALE POISONOUS GAS If refrigerant gas comes in contact with flame, a poisonous
gas is prodused. During leak tests, do not inhale any gas.
Precautions When Replacing Parts in
Refrigerant Line
1. RECOVER REFRIGERANT IN SYSTEM BEFOREREMOVING PARTS
Using a recovery machine, recover refrigerant in system be-
fore removing the parts.
NOTICE: Do not release refrigerant to atmosphere.
2. INSERT PLUG IMMEDIATELY IN DISCONNECTED PARTS
Insert a plug immediately in the disconnected parts to pre-
vent the entry of moisture and dust.
3. DO NOT REMOVE PLUG FROM NEW PARTS UNTIL
IMMEDIATELY BEFORE INSTALLATION
4. DO NOT USE BURNER FOR BENDING OR LENGTHENING OPERATIONS ON TUBE
If the tubes are heated with a burner, a layer of oxidation
forms inside the tube, causing the same kind of trouble as an
accumulation of dust.
5. DISCHARGE GAS IN NEW COMPRESSOR FROM
CHARGING VALVE BEFORE INSTALLING IT
If the gas in new compressor is not discharged first, compres-
sor oil will spray out with gas when the plug is removed.
6. TIGHTEN CONNECTING PARTS SECURELY Securely tighten the connecting parts to prevent leaking of
refrigerant gas.
wApply a few drops of compressor oil to O±ring fittings for
easy tightening and to prevent leaking of refrigerant
gas.
w Tighten the nuts using two wrenches to avoid twisting
the tube.
AC±4
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AIR CONDITIONING SYSTEM General Description
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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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DIAGNOSTIC CODE CHART
If a malfunction code is displayed during the diagnostic code check (sens\
or check), check the circuit listed for
that code in the table below (Proceed to the page given for that circuit.)\
Code No.Diag. Code Detecting Condition
00 Normal
11 *1 Open or short in room temperature sensor circuit.
12 Open or short in ambient temperature sensor circuit.
13 Open or short in evaporator temperature sensor circuit.
14*2 Open or short in water temperature sensor circuit.
21*3 Open in solar sensor circuit.
21*3
 Short in solar sensor circuit.
22*4
 All conditions below are detected for 3 secs. or more.
 (a) Engine rpm : 450 rpm or more.
 (b) Ratio between engine and compressor rpm deviates 20% or more in c\
omparison to normal
operation.
23
 Open in pressure sensor circuit.
 Abnormal refrigerant pressure below 206 kPa (2.1 kgf/cm, 30 psi)
over 2,650 kPa (27 kgf/cm, 385 ps\
i)
31 Short to ground or power source circuit in Air Mix Damper position sens\
or circuit.
32 Short to ground or power source circuit in Air Inlet Damper position se\
nsor circuit.
33 Short to ground or power source circuit in Air Outlet Damper position s\
ensor circuit.
41 Air mix damper position sensor value does not change even if ECU operat\
es air mix servomotor.
42 Air inlet damper position sensor value does not change even if ECU oper\
ates air inlet servomotor.
43 Air outlet damper position sensor value does not change even if ECU ope\
rates air outlet
servomotor.
HINT: *1 If the room temp. is approx. ±20 °C (±4 °F) or lower, code 11 may be output even though the system
is normal.
*2 If the ambient temperature is approx. ±50 °C (±58 °F) or lower, a malfunction code may be output
even though the system is normal.
*3 If the check is being performed in a dark place, diagnostic code 21 (so\
lar sensor circuit abnormal) could be displayed.
In this case, perform diagnostic code check again while shining a light,\
such as an inspection light,
on the solar sensor.
If code 21 is still displayed, there could be trouble in the solar senso\
r circuit
AC±28
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AIR CONDITIONING SYSTEM Troubleshooting
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