1991 LEXUS SC400 warning light

INSPECTION OF HAZARD WARNING
SWITCH
INSPECTION HAZARD WARNING SWITCH(Continuity)
Inspect the switch continuity between terminals.
If continuity is not as specified, replace the switch.
(Switch Circuit)
Disconnect the switch connector and inspect the connection
on the wire harness side as shown.
Check forTester connectionConditionSpecified value
Voltage8±GroundConstantBattery positive voltage
10±GroundIgnition switchpositionLOCK or ACCNo voltage10±GroundIgnition switch positionONBattery positive voltage
*12±GroundLight control switchpositionOFFNo voltage*12±GroundLight control switch positionTAIL or HEADBattery voltage
Continuity*13±GroundConstantContinuity
5±GroundConstant*2Continuity
6±GroundConstant*2Continuity
*1: Illumination*2: There is resistance because this circuit is grounded through the bulb.\
If the circuit is not as specified, refer to BE±66 wiring diagram
and inspect the circuits connected to other parts.
±
BODY ELECTRICAL SYSTEM Lighting SystemBE±69
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TROUBLESHOOTING
Turn Signal and Hazard Warning Light
System
You will find the cause of trouble more easily using the table shown below. In this table, the numbers indicate
the order priority of the causes in trouble. Check each part in the order \
shown. If necessary, replace the parts.
See pagePart
name
Trouble
ªHazardº and ªTurnº do not light up.
The flashing frequency is abnormal.
Hazard warning light does not light up.
(Turn is normal.)
Hazard warning light does not light up
in one direction.
*  Turn signal does not light up.
*

Turn signal does not light up.
Turn signal does not light up in one direction.
Only one bulb does not light up.
*
: Combination Meter, Wiper and Washer do not operate.
*  : Combination Meter, Wiper and Washer are normal.
HAZ±HORN Fuse
TURN Fuse
Ignition Switch
Hazard Warning Switch
Turn Signal Flasher
Turn Signal Switch
Wire Harness
Bulb
BE±4
, 21
BE±4
, 20
BE±26
BE±68
BE±68
BE±46
BE±6
BE±70±
BODY ELECTRICAL SYSTEM Lighting System
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DESCRIPTION
The combination meter has various meters and gauges which show the vehicle'\
s condition, warning lights which
monitor abnormalities in the vehicle and inform the driver, indicator lights which inform the driver of the condition
of each part of vehicle, and a function for illumination and brightness ad\
justment of meters and gauges.
The component parts of this system and their functions are described in \
the following table.
Parts NameFunction
SpeedometerThe speedometer needle moves in accordance with signals from the speed s\
ensor to
indicate the vehicle's speed.
TachometerThe tachometer needle moves in accordance with signals from the igniter \
to indicate the
engine's speed.
Water Temperatrue
GaugeThe water temperature gauge's needle moves in accordance with signals from the send-
er gauge and indicates the temperature of the engine coolant.
Fuel GaugeThe fuel gauge needle moves in accordance with signals from the sender g\
auge, indicat-
ing the amount of fuel remaining in the fuel tank.
OdometerThe odometer counts the total distance traveled by the vehicle in accord\
ance with pulse
signals from the speed sensor.
Twin Trip Switch
The twin trip meter counts the distance traveled by the vehicle in accor\
dance with pulse
signals from the speed sensor. It can be reset using a switch and can be used to switch
between trip meters A and B.
Circuit Plate
This plate contains the circuitry for each meter and gauge and for each \
warning light and
indicator light, as well as an internal engine oil level warning drive c\
ircuit, drive circuits for
the odometer and trip meter and brightness adjustment circuitry for each\
indicator.
Speed SensorMounted in the transmission, this sensor outputs pulse signals to the co\
mbination meter
in accordance with the speed of the output shaft.
Twin Trip SwitchOperation of this switch switches between the A and B trip meters and se\
nds reset sig-
nals to the combination meter.
Water
Temperature Sender
GaugeThis sender converts engine coolant temperatures to a resistance value i\
n signal form to
the combination meter.
Fuel Sender GaugeThis sender converts the level of fuel remaining in fuel tank to resista\
nce value and
sends the resistance value in signal form to combination meter.
Rheostat Light
Control VolumeIn order to adjust the degree of illumination of the combination meter, the resistance val-
ue of the built±in variable resistor is sent to the combination meter\
and rheostat light
control.
Fuel Level Warning
SwitchWhen the level of fuel remaining falls below a predetermined level, cont\
inuity is estab-
lished with this switch, which is built into the fuel sender gauge, caus\
ing a warning light
to light up.
Low Oil Pressure
Warning SwitchThis switch is mounted on the engine block. Continuity is established in\
this switch when
the oil pressure is low, causing a warning light to light up.
Integration Relay (Seat
Belt Warning Relay)
This relay receives current from fuse GAUGE and DOME and is connected to\
each
buckle switch, door courtesy switch, key unlock warning switch and warni\
ng light. As
part of the seat belt warning system, it sounds a chime and lights a war\
ning light when
seat belts are unfastened. As part of the key unlock warning system, it \
sounds a chime
when the set conditions are fulfilled.
Light Failure SensorThis sensor senses when a bulb in rear combination light is burnt out an\
d lights up a
warning light.
BE±96±
BODY ELECTRICAL SYSTEM Combination Meter
WhereEverybodyKnowsYourName

Parts NameFunction
Coolant Level
Warning SwitchThis switch is installed in the radiator reservoir tank. It lights up a \
warning light when the
coolant level becomes low.
Engine Oil Level
Warning SwitchThis switch is mounted in the engine oil pan. It lights a warning light \
when the engine oil
level is low.
Brake Fluid Level
Warning SwitchThis switch is mounted in the brake master cylinder reservoir tank. It l\
ights up a warning
light when the brake fluid level is low.
Parking Brake SwitchThis switch is on the parking brake lever bracket. Continuity in this sw\
itch is established
when the lever is released, causing a warning light to light up.
Door Courtesy SwitchContinuity is established in this switch when a door is opened, causing \
a warning light to
light up.
Warning LightsWhen an abnormality is detected in the vehicle, current is sent to these\
lights, or they are
grounded, causing them to light up.
Indicator LightsCurrent is sent to these lights, or they are grounded, causing them to l\
ight up and indicate
the vehicle's condition to the driver.
Window Washer Level
Warning SwitchThis switch is mounted in the window washer tank. It lights a warning li\
ght when the
window washer level becomes low.
±
BODY ELECTRICAL SYSTEM Cominbation MeterBE±97
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ConnectionCheck forTester connectionConditionSpecified value
Turn signalHazard warning switch ONBattery positiveTurn signal
SW andB 16 Ground
Hazard warning switch ONBattery ositive
voltage e 0V
HazardB±16±Ground
IG SW ON and turn signal SW ºLeftºBattery positive
Warning
Si hVoltage
IG SW ON and turn signal SW ºLeftºBattery ositive
voltage e 0V
SwitchVoltage
Hazard warning switch ONBattery positive
B 17 Ground
Hazard warning switch ONBattery ositive
voltage e 0VB±17±Ground
IG SW ON and turn signal SW ºRightºBattery positiveIG SW ON and turn signal SW ºRightºBattery ositive
voltage e 0V
HeadlightLi ht t l SWDimmer SW ºHIº orBattery positiveHeadlight
VoltageB7±GroundLight control SW
ºHEADº
Dimmer SW HI or
ºFlashº
Battery ositive
voltageVoltageB7±GroundºHEADºDimmer SW ºLOºNo voltage
ContinuityB6±GroundLight control SW
º
HEADº
Dimmer SW ºHIº or
ºFlashºContinuityContinuityB6 GroundºHEADºDimmer SW ºLOºNo continuity
IgniterVoltageA9±GroundEngine RunningVoltage
fluctuates
ECT patternVoltageB4 GroundIG SW ON and ECT patternPWRBattery positive voltageECT attern
Select switchVoltageB4±GroundIG SW ON and ECT attern
select SW positionNORMNo voltage
Engine oilOil temperature below approx. 55 5C (131 5F)Continuityg
Level warn-
ing Switch
ContinuityB8±Ground
Oil temperature
above approx. 55 5CON (float up)ContinuitygContinuityB8 Groundabove a rox. 55 C
(131 5F) and SW
positionOFF (float off)No continuity
GAUGE fuseVoltageA1 GroundIgnition switchONBattery positive voltageVoltageA1±GroundIgnition switch
positionLOCK, ACC, STARTNo voltage
Neutral StartVoltageA12±GroundIgnition switch
position
START (ºPº or ºNº
range)Battery positive voltage
switch
VoltageA12 GroundpositionLOCK, ACC, ONNo voltage
ECU±BVoltageC11 GroundIgnition switchONBattery positive voltage
FuseVoltageC11±GroundIgnition switch
positionLOCK, ACC, STARTNo voltage
Rheostat
Li ht t l
ON (Rheostat knob
t d itiBtt ltLight control
VolumeLight control SWturned any position
except fully clock-
Battery voltage or
5V or moreVolume
VoltageA2±Ground
g
HEAD or TAIL and
rheostat volume
except fully clock-
wise)5V or more
VoltageA2 Groundrheostat volume
knob positionOFF (Rheostat knob)
turned fully clockNo voltageknob ositionturned fully clock-
wise)No voltage
GroundA8±GroundConstantContinuity
ContinuityA10±GroundConstantContinuityContinuityA22±GroundConstantContinuity
A23±GroundConstantContinuity
*1 Jack up the vehicle.*2 Shift lever position is ºPº range.
If circuit is not as specified, refer to BE±100 wiring diagrams
and inspect the circuits connected to other parts.
BE±108
±
BODY ELECTRICAL SYSTEM Combination Meter
WhereEverybodyKnowsYourName

TROUBLESHOOTING
How to proceed with troubleshooting
Perform troubleshooting in accordance with the procedure on the followin\
g page.

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.
CHECK AND CLEAR THE DIAGNOSTIC TROUBLE CODES (PRECHECK)
If the TRAC indicator light lights up, and the TRAC control does not ope\
rate, the ECU stores diagnostic
trouble codes corresponding to the problem in memory.
Before confirming the trouble, first check the diagnostic trouble code for any\
malfunction codes stored in
memory. When there are malfunction codes, make a note of them, then clear them and proceed to ª 
Problem Symptom Confirmationº.
 PROBLEM SYMPTOM CONFIRMATION,  SYMPTOM SIMULATION
Confirm the problem symptoms. If the problem does not reoccur, simulate the problem by initially checking
the circuits indicated by the diagnostic trouble code in step , using ªProblem simulation methodº.
 DIAGNOSTIC TROUBLE CODE CHECK
Check the diagnostic trouble codes. If a malfunction code is output, proceed \
to ª  Diagnostic Trouble
Code Chartº.
If the normal code is output, proceed to ª  Problem Symptoms Chartº.
Be sure to proceed to ª  diagnostic Trouble Code Chartº after steps and  are completed.
If troubleshooting is attempted only by following the malfunction code sto\
red in the memory, errors could
be made in the diagnosis.
 DIAGNOSTIC TROUBLE CODE CHART
If a malfunction code is confirmed in the diagnostic trouble code check,\
proceed to the inspection proce-
dure indicated by the matrix chart for each diagnostic trouble code.
 PROBLEM SYMPTOMS CHART
If the normal code is confirmed in the diagnostic trouble code check, perf\
orm inspection in accordance with
the inspection order in the problem symptoms chart.
 CIRCUIT INSPECTION
Proceed with diagnosis of each circuit in accordance with the inspection\
order confirmed in  and .
Determine whether the cause of the problem is in the sensor, actuators, wire harness and connectors or
the ECU.
\b SENSOR CHECK
Use the ABS warning light to check if each of the signals from speed sensors is \
being input correctly to
the ECU. Instructions for this check are given in the circuit inspection\
.
[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 eliminated\
, but also conduct a test drive
to make sure the entire TRAC system is operating correctly. And also check the ABS is operating correctly.
BR±166
±
BRAKE SYSTEM TRACTION CONTROL SYSTEM (TRAC)
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DIAGNOSTIC TROUBLE CODE CHART
If a malfunction code is displayed during the diagnostic trouble code chec\
k, check the circuit listed for that code
in the table below and proceed to the page given.
HINT: If the TRAC indicator light lights up and the TRAC indicator light doe\
s not blink when the Diag. code is
checked, check the blinking pattern of the ABS warning light and perform trouble\
shooting of the ABS system.
BR±186BR±189
BR±190
BR±192
BR±196 BR±198
BR±200
BR±208
BR±216
BR±218
BR±220BR±189
BR±189
BR±190
BR±190
BR±190
BR±200 BR±208
*1: If a malfunction is detected, the TRAC OFF indicator light lights up.
*2: Indicator light does not lights up even if an error is detected.
*3: If a malfunction is detected, the TRAC OFF indicator light or TRAC i\
ndicator light light up.
BR±172
±
BRAKE SYSTEM TRACTION CONTROL SYSTEM (TRAC)
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TRAC OFF Indicator, TRAC Cut Switch Circuit
CIRCUIT DESCRIPTION
This is the TRAC control main switch. When the TRAC cut switch is pushed on,\
TRAC control goes off and
the TRAC OFF indicator lights up. This indicator is also used for warnings \
when the trouble occurs.
DIAGNOSTIC CHARTDIAGNOSTIC CHART
BR±222±
BRAKE SYSTEM TRACTION CONTROL SYSTEM (TRAC)
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