warning lights LEXUS SC400 1991 Service Owner's Manual

WIRING DIAGRAM
ABS Warning Light Circuit
CIRCUIT DESCRIPTION
If the ECU detects trouble, it lights the ABS warning light while at the s\
ame time prohibiting ABS control.
At this time, the ECU records a diagnostic trouble code in memory.After removing the short pin of the DLC1,
connect a DLC1 or connect terminals Tc and E1 of the DLC2 to make the ABS warning light to blink and
output the diagnostic trouble code.DIAGNOSTIC CHARTPerform troubleshooting in accordance with the
chart below for each trouble symptom.
DIAGNOSTIC CHARTDIAGNOSTIC CHART
Perform troubleshooting in accordance with the chart below for each trouble sym\
ptom.
 


ABS warning light does not light up 


Go to step
 

ABS warning light remains on 

Go to step
BR±144±
BRAKE SYSTEM ANTI±LOCK BRAKE SYSTEM (ABS)
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The EFI system is composed of three basic sub±systems: Fuel, Air Induction and Elect\
ronic Control
Systems.
FUEL SYSTEM
An electric pump fuel pressure supplies sufficient fuel, under a constant pressure, to the EFI injectors. In
accordance with signals from the ECU (Electronic Control Unit), these \
injectors inject the quantity of fuel most
appropriate for the engine condition into the intake manifold.
AIR INDUCTION SYSTEM
The air induction system provides sufficient air for engine operation.
ELECTRONIC CONTROL SYSTEM
The 1UZ±FE engine (ECU±formerly EFI computer) with a microcomputer \
centrally controls the EFI, ESA,
ISC and Diagnosis system, etc. The ECU controls the following functions:
1. Electronic Fuel Injection (EFI)
The ECU receives signals from various sensors indicating changing engine op\
eration conditions such as:Intake air volume
Intake air temperature
Coolant temperature
Engine rpm
Acceleration/deceleration
Exhaust oxygen content etc.
The signals are utilized by the ECU to determine the injection duration nec\
essary for an optimum air±fuel
ratio.
2. Electronic Spark Advance (ESA) The ECU is programmed with data for optimum ignition timing under any and all opera\
ting conditions. Using
data provided by sensors which monitor various engine functions (rpm, coola\
nt temperature, etc.), the
Electronic Control Unit (ECU) triggers the spark at precisely right instant. (S\
ee IG section)
3. Idle Speed Control (ISC) The ECU is programmed with idle speed data for various engine conditions (\
coolant temperature, air condi-
tioner ON/OFF, etc.).
The air volume flowing through the throttle valve by±pass passage is adj\
usted according to the signal from
each sensor and the idle speed is kept at the set value.
4. Diagnosis Function When the ECU detects any malfunctions or abnormalities in the sensor network\
, it lights the ºCHECKº en-
gine warning light in the combination meter. At the same time, the trouble is identified and a diagnostic code
is recorded by the ECU. The diagnostic code can be read by the number of\
blinks of the ºCHECKº engine
warning light when terminals TE1 and E1 are connected. The diagnostic co\
des are refer to the later page.
(See TR section)
5. Self±Correction Function If any sensor malfunctions, an average value recorded in the back±up ci\
rcuit is substituted to make driving
possible.
If danger is predicted, the engine is stopped and the ºCHECKº engine\
warning light will light up.
6. Fail±Safe Function Even if an abnormality occurs in the ECU, the back±up circuit uses a specifie\
d fuel injection and ignition
timing to provide vehicle driveability, and also lightsup the ºCHECKº engine warning light.
FI±4
EFI SYSTEM
± Description
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GENERAL MAINTENANCE
MA00M±03
There are the maintenance and inspection
items which are considered to be the owner's
responsibility. They can be performed by the
owner or be can have them done at a service
shop. These items include those which should
be checked on a daily basis, those which, in
most cases, do not require (special) tools and
those which are considered to be reasonable
for the owner to perform. Items and procedures
for general maintanance are as follows:
MA00P±04
OUTSIDE VEHICLE
1. TIRES
(a) Check the pressure with a gauge. Adjust ifnecessary.
(b) Check for cuts, damage or excessive wear.
2. WHEEL NUTS Wheel checking the tires, check the nuts for
looseness or for missing nuts. If necessary,
tighten them.
3. TIRE ROTATION It is recommended that tires be rotated every
12,000 km (7,500 miles).
4. WINDSHIELD WIPER BLADES Check for wear or cracks whenever they do not
wipe clean. Replace if necessary.
5. FLUID LEAKS
(a) Check underneath for leaking fuel, oil, water or
other fluid.
(b) If you smell gasoline fumes or notice any leak, have the cause found and corrected.
6. DOORS AND ENGINE HOOD
(a) Check that all doors including the trunk lid operate smoothly, and that all latches lock
securely.
(b) Check that the engine hood secondary latch secures the hood from opening when the
primary latch is released.
MA00R±05
INSIDE VEHICLE
7. LIGHTS
(a) C h e c k t h a t t h e h eadlights, stop lights,
tail±lights, turn signal lights, and other lights
are all working. (b) Check the headlight aiming.
8. WARNING LIGHT AND BUZZERS
Check that all warning lights and buzzers func-
tion properly.
9. HORN Check that it is working.
10. WINDSHIELD GLASS
Check for scratches, pits or abrasions.
11. WINDSHIELD WIPER AND WASHER
(a) Check operation of the wipers and washer.
(b) Check that the wipers do not streak.
12. WINDSHIELD DEFROSTER Check that the air comes out from the defroster
outlet when operating the heater air condition-
er at defroster mode.
13. REAR VIEW MIRROR
Check that it is mounted securely.
14. SUN VISORS Check that they move freely and are mounted
securely.
15. STEERING WHEEL Check that it has the specified freeplay. Be
alert for changes in steering condition, such as
hard steering, excessive freeplay or strange
noise.
16. SEATS
(a) Check that all front seat controls such as seat adjusters, seatback recliner, etc. operate
smoothly.
(b) Check that all latches lock securely in any position.
(c) Check that the locks hold securely in any latched position.
(d) Check that the head restraints move up and
down smoothly and that the locks hold securely
in ay latches position.
(e) For folding±down rear seat backs, check that the latches lock securely.
17. SEAT BELTS
(a) Ch e ck th a t th e se a t be lt syste m su ch as buckles, retractors and anchors operate
properly and smoothly.
(b) Check that the belt webbing is not cut, frayed,
worn or damaged.
18. ACCELERATOR PEDAL Check the pedal for smooth operation and un-
even pedal effort or catching.
±
MAINTENANCE (1UZ ± FE)MA±19
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The EFI system is composed of three basic sub±systems: Fuel, Air Induction and Elect\
ronic Control
Systems.
FUEL SYSTEM
An electric pump fuel pressure supplies sufficient fuel, under a constant pressure, to the EFI injectors. In
accordance with signals from the ECU (Electronic Control Unit), these \
injectors inject the quantity of fuel most
appropriate for the engine condition into the intake manifold.
AIR INDUCTION SYSTEM
The air induction system provides sufficient air for engine operation.
ELECTRONIC CONTROL SYSTEM
The 1UZ±FE engine (ECU±formerly EFI computer) with a microcomputer \
centrally controls the EFI, ESA,
ISC and Diagnosis system, etc. The ECU controls the following functions:
1. Electronic Fuel Injection (EFI)
The ECU receives signals from various sensors indicating changing engine op\
eration conditions such as:Intake air volume
Intake air temperature
Coolant temperature
Engine rpm
Acceleration/deceleration
Exhaust oxygen content etc.
The signals are utilized by the ECU to determine the injection duration nec\
essary for an optimum air±fuel
ratio.
2. Electronic Spark Advance (ESA) The ECU is programmed with data for optimum ignition timing under any and all opera\
ting conditions. Using
data provided by sensors which monitor various engine functions (rpm, coola\
nt temperature, etc.), the
Electronic Control Unit (ECU) triggers the spark at precisely right instant. (S\
ee IG section)
3. Idle Speed Control (ISC) The ECU is programmed with idle speed data for various engine conditions (\
coolant temperature, air condi-
tioner ON/OFF, etc.).
The air volume flowing through the throttle valve by±pass passage is adj\
usted according to the signal from
each sensor and the idle speed is kept at the set value.
4. Diagnosis Function When the ECU detects any malfunctions or abnormalities in the sensor network\
, it lights the ºCHECKº en-
gine warning light in the combination meter. At the same time, the trouble is identified and a diagnostic code
is recorded by the ECU. The diagnostic code can be read by the number of\
blinks of the ºCHECKº engine
warning light when terminals TE1 and E1 are connected. The diagnostic co\
des are refer to the later page.
(See TR section)
5. Self±Correction Function If any sensor malfunctions, an average value recorded in the back±up ci\
rcuit is substituted to make driving
possible.
If danger is predicted, the engine is stopped and the ºCHECKº engine\
warning light will light up.
6. Fail±Safe Function Even if an abnormality occurs in the ECU, the back±up circuit uses a specifie\
d fuel injection and ignition
timing to provide vehicle driveability, and also lightsup the ºCHECKº engine warning light.
FI±4
EFI SYSTEM
± Description
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DIAGNOSIS SYSTEM
DESCRIPTION
The ECU contains a built±in self±diagnosis system by which
troubles with the engine signal network are detected and a
ºCHECKº engine warning light on the instrument panel lights up.
By analyzing various signals as shown in the later table (See page
TR±14) the Electronic Control Unit (ECU) detects system malfunc-
tions relating to the sensors or actuators.
In the normal mode, the self±diagnosis system monitors 22 (USA
specification vehicles with TRAC control) or 21 (USA (except for
California) and Canadian specification vehicles with TRAC con-
trol) items, indicated by code No. as shown in TR±14. A ºCHECKº
engine warning light informs the driver that a malfunction has been
detected. The light goes off automatically when the malfunction
has been repaired. But the diagnostic code(s) remains stored in
the ECU memory (except for code Nos. 16 and 53). The ECU
stores the code(s) until it is cleared by removing the EFI fuse with
the ignition switch off.
The diagnostic code can be read by the number of blinks of the
ºCHECKº engine warning light when TE1 and E1 terminals on the
TDCL or check connector are connected. When 2 or more codes
are indicated, the lowest number (code) will appear first.
In the test mode, 15 (USA specification vehicles with TRAC con-
trol) or 14 (USA (except for California) and Canadian specification
vehicles with TRAC control) items, indicated by code No. as
shown in TR±14 are monitored. If a malfunction is detected in any
one of the systems indicated by code Nos. 13, 21, 22, 24, 25, 26,
27, 28, 29, 35, 41, 42, 47, 71 and 78 (USA specification vehicles)
or 13, 21, 22, 24, 25, 26, 27, 28, 29, 35, 41, 42, 47 and 78 (USA
(except for California) and Canadian specification vehicles) the
ECU lights the ºCHECKº engine warning light to warn the techni-
cian that malfunction has been detected. In this case, TE2 and E1
terminals on the TDCL should be connected as shown later. (See
page TR±12 ).
In the test mode, even if the malfunction is corrected, the malfunc-
tion code is stored in the ECU memory even when the ignition
switch is off (except code Nos. 43 and 51). This also applies in the
normal mode. The diagnostic mode (normal or test) and the output
of the ºCHECKº engine warning light can be selected by connect-
ing the TE1, TE2 and E1 terminals on the check connector or
TDCL, as shown later.
A test mode function has been added to the functions of the self±
diagnosis system of the normal mode for the purpose of detecting
malfunctions such as poor contact, which are difficult to detect in
the normal mode. This function fills up the selfdiagnosis system.
The test mode can be implemented by the technician following the
appropriate procedures of check terminal connection and opera-
tion described later. (See page TR±12)
TR±10
±
ENGINE TROUBLESHOOTING Diagnosis System
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Trouble Area
ºCHECKº
Engine Warning
Light*

Memory* See PageTrouble Area
Normal
ModeTest
Mode
MemorySee Page
w Open or short in EGR step motor circuit.ONNA Oen or short in EGR ste motor circuit.
w ECUONN.A.
w Open in EGR gas temp. sensor circuit.ONON
TR±108 Oen in EGR gas tem . sensor circuit.
w ECUONON
w Open or short in fuel pump ECU circuit.
w Fuel pump ECU
w Engine & ECT ECU power source circuit.
w Fuel pump
w Engine & ECT ECU
ONONTR±114
w A/C switch circuit
w Throttle position sensor IDL circuit
w Neutral start switch circuit.
w Accelerator pedal and cable
w ECU
N.A.OFFXTR±118
*4: This indicates items for which º2 trip detection logicº is used. With this logic, when a lo\
gic malfunction is
first detected, the malfunction is temporarily stored in the ECU memory. If the same case is detected again
during the second drive test, this second detection causes the ºCHECK\
º Engine Warning Light to light up.
The 2 trip repeats the same mode a 2nd time. (However, the IG switch must be turned OFF between the
1st trip and 2nd trip).
In the Test Mode, the ºCHECKº Engine Warning Light lights up the 1st trip a malfunction is detected.
±
ENGINE TROUBLESHOOTING Diagnostic Code ChartTR±21
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CHECK FOR MOMENTARY
INTERRUPTION
As described in the preceding paragraph, abnormality detection
ability in the test mode is increased compared to that in the normal
mode, so that when momentary interruptions or momentary shorts
occur in the ECU signal circuits (G1, G2, NE, THW, THA, VTA1,
VTA2) shown in the table below, the appropriate diagnostic code
is output.
Accordingly, when the diagnostic codes shown in the table below
(13, 22, 24, 41, 47) are output during the diagnostic code check,
and inspection of the appropriate circuits reveals no abnormality,
perform the check for momentary interruption as described below.
By performing the check for momentary interruption, the place
where momentary interruptions or momentary shorts are occur-
ring due to poor contacts can be isolated.
CLEAR DIAGNOSTIC CODES
See page TR±13.
SET TEST MODE
1. With the ignition switch off, using SST, connect the terminals
TE2 and E1 of the TDCL.
SST 09843±18020
2. Start the engine and check to see the ºCHECKº engine warning light to go off.
PERFORM A SIMULATION TEST
Using the symptom simulation (See page IN±20), apply vibration
to and pull lightly on the wire harness, connector or terminals in the
circuit indicated by the malfunction code.
In this test, if the ºCHECKº engine warning light lights up, it in\
di-
cates that the place where the wire harness, connector or termi-
nals being pulled or vibrated has faulty contact. Check that point
for loose connections, dirt on the terminals, poor fit or other prob-
lems and repair as necessary.
HINT: After cancelling out the diagnostic code in memory and set
the test mode, if the ºCHECKº engine warning light does not go off
after the engine is started, check thoroughly for faulty contact,
etc., then try the check again. If the ºCHECKº engine warning light
still does not go off, check and replace ECU.
±
ENGINE TROUBLESHOOTING Check for Momentary InterruptionTR±23
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WIRING DIAGRAM
SRS Warning Light System (Always Lit Up, when ignition switch in
LOCK position)
CIRCUIT DESCRIPTION
The SRS warning light is located on the combination meter.
When the supplemental restraint system is normal, the SRS warning light ligh\
ts up for approx. 6 seconds after
the ignition switch is turned from LOCK position to ACC or ON position, and\
then turns off automatically.
If there is a malfunction in the supplemental restraint system, the SRS wa\
rning light lights up to inform the driver
of the abnormality.
When terminals Tc and E
1 of the DLC2 are connected, the diagnostic trouble code is displayed by \
the blinking
of the SRS warning light.
DIAGNOSTIC CHARTDIAGNOSTIC CHART
HINT: If the SRS warning light is always lit up by a DTC check procedure, per\
form Tc T erminal circuit check proce-
dure (See page RS±121).
±
SUPPLEMENTAL RESTRAINT SYSTEM TROUBLESHOOTINGRS±119
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SRS WARNING LIGHT CHECK
DIAGNOSIS INSPECTION
(a) Turn the ignition switch to ACC or ON and check that the SRSwarning light lights up.
(b) Check that the SRS warning light goes out after approx. 6
seconds.
HINT:
wWhen the ignition switch is at ACC or ON and the SRS
warning light remains on, the TROUBLESHOOTING
has detected a malfunction code.
w If, after approx. 6 seconds have elapsed, the SRS
warning light sometimes lights up or the SRS warning
light lights up even when the ignition switch is OFF, a
short in the SRS warning light circuit can be considered
likely. Proceed to SRS warning light system (always lit
up when ignition switch LOCK position) on page
RS±119 .
DIAGNOSTIC TROUBLE CODE CHECK
Using diagnosis check wire:
1. OUTPUT DIAGNOSTIC TROUBLE CODE
(a) Turn the ignition switch to ACC or ON position and wait approx. 20 seconds.
(b) Using SST, connect terminals Tc and E of the DLC2. SST 09843±18020
NOTICE: Never make a mistake with the terminal connec-
tion position as this will cause a malfunction.
±
SUPPLEMENTAL RESTRAINT SYSTEM TROUBLESHOOTINGRS±59
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DIAGNOSTIC TROUBLE CODE MATRIX 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 (Proceed to the page given for that circuit).
 DTC No.\
 \
Diagnosis Page
 (Normal)*1\
 \

Source voltage drop RS±68
 11\
 \

Short in squib circuit or front airbag sensor circuit (to ground) RS±70
 12\
 \

Short in squib circuit or front airbag sensor circuit (to B+) RS±78
 13\
 \

Short in squib circuit (between D+ wire harness and D± wire harness\
) RS±85
 14\
 \

Open in squib circuit (between D+ wire harness and D± wire harness)\
 RS±92
 15\
 \

Open in front airbag sensor circuit RS±97
 22*2\
 \

SRS warning light system malfunction RS±102
 31\
 \

Center airbag sensor assembly malfunction RS±108
 53\
 \

Short in squib circuit (between P+ wire harness and P± wire harness\
) RS±110
 54\
 \

Open in squib circuit (between P+ wire harness and P± wire harness)\
 RS±115
HINT:
*
1 When the SRS warning light remains lit up and the diagnostic trouble co\
de is the normal code, this means
a source voltage drop.
*
2 Code 22 is recorded when a malfunction occurs in the SRS warning light \
system. If an open malfunction
occurs in the SRS warning light system, the SRS warning light does not light up, s\
o that until the malfunction
is repaired, the diagnostic trouble code (including 22) cannot be conf\
irmed.
PROBLEM SYMPTOM CHART
Proceed with troubleshooting of each circuit in the table below.
\
 \
Problem Symptom Inspection Item Page
\
 

\



With the ignition switch at ACC or ON, the SRS warning light
sometimes lights up after approx. 6 seconds have elapsed
SRS warning light system
(Always lit upwhen ignition switch isRS±119\
 

\



SRS warning light lights up even when ignition switch is in
the LOCK position (Always lit up when ignition switch is
LOCK position)RS±11 9
\
 \

Diagnostic trouble code not displayed.
Tc terminal circuitRS±121
\
 \

Diagnostic trouble code continuously displayed.
Tc terminal circuitRS±121
±
SUPPLEMENTAL RESTRAINT SYSTEM TROUBLESHOOTINGRS±67
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