1991 LEXUS SC400 brakes

DTC46No. 4 Solenoid Valve Circuit (For Accumula-
tor Back Pressure Modulation)
CIRCUIT DESCRIPTION
The No. 4 solenoid valve controls the hydraulic pressure acting on the
brakes and clutches of the planetary gear units when gears are shifted and
performs smooth gear shifting.
The ECM determines optimum operating pressure according to the signals
from the throttle position sensor, vehicle speed sensor and O/D clutch
speed sensor and controls the volume of current flow to the solenoid valve.
The amount of electric current to the solenoid is controlled by the (*) \
duty
ratio of ECM out put signals, causing momentary change to the hydraulic
pressure acting on the clutches during gear shifting.
When the duty ratio is high, the hydraulic pressure acting on the clutch\
es
is low.
(*) Duty Ratio
The duty ration is the ration of the period of continuity in one cycle. For\
example, if A is the period of continuity
in one cycle, and B is the period of non±continuity, then
DTC No.DTC Detecting ConditionTrouble Area
46
All conditions below are detected for 1 sec. or more.
2trip detection logic*
(a) ECM outputs duty signal to No. 4 solenoid in 90%
or higher duty ratio.
(b) Current to No. 4 solenoid:330
100 Ma OR LESS
(O/D OFF indicator light doesn't blink)
 No. 4 solenoid valve.
 Harness or connector between No. 4 sole-
noid valve and ECM
 ECM
*: See page AT±62.
Reference Reference
 Waveform between terminals SLN± and E
1when engine is idling. 
Waveform between terminals SLN± and E1 during shift
change.
AT±82±
A304E (1UZ±FE) AUTOMATIC TRANSMISSION TROUBLESHOOTING
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AT±66BE
IN±33
WIRING DIAGRAM
Stop Light Switch Circuit
CIRCUIT DESCRIPTION
The purpose of this circuit is to prevent the engine from stalling, while d\
riving in lockup condition, when
brakes are suddenly applied.When the brake pedal is operated, this switch sends a signal to ECM. Then
the ECM cancels operation of the lockup clutch while braking is in progress\
.
DIAGNOSTIC CHARTDIAGNOSTIC CHART
AT±108±
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IN±33
WIRING DIAGRAM
TT Terminal Circuit
CIRCUIT DESCRIPTION
Checks of ECM input and output signals related to the throttle position sensor\
brakes, shift position and
other circuits can be performed by measuring the voltages at terminal T
T of the DLC1.
DIAGNOSTIC CHARTDIAGNOSTIC CHART
AT±120±
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2. HYDRAULIC CONTROL SYSTEMThe hydraulic control system is composed of the oil pump, the valve body, the solenoid valves, the accumu-
lators, the clutches and brakes, as well as the fluid passages which connect al\
l of these components.
Based on the hydraulic pressure created by the oil pump, the hydraulic control system governs the hydrau-
lic pressure acting on the torque converter clutch, clutches and brakes \
in accordance with the vehicle driv-
ing conditions.
There are 4 solenoid valves on the valve body.
The No.1 and No.2 solenoid valves are turned on and off by signals from the ECM to operate the shift
valves, and change the gear shift position.
The No.3 solenoid valve is operated by signals from the ECM to engage or di\
sengage the lock±up clutch
of the torque converter clutch.
The No.4 solenoid valve is operated by signals from the ECM to control the \
engagement speed and reduce
gear shift shock.
±
A304E (1UZ±FE) AUTOMATIC TRANSMISSION OPERATIONAT±7
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GENERAL DESCRIPTION
BR03E±06
1. Care must be taken to replace each part properly as it could affect the \
performance of the brakesystem and result in a driving hazard. Replace the parts with parts of the same part number or
equivalent.
2. It is very important to keep parts and the area clean when repairing the\
brake system.
3. If the vehicle is equipped with a mobile communication system, refer to the precaution \
in the IN section.
DESCRIPTION
BR03F±03
The service brakes consist of a foot brake which changes rotational energy to therma\
l energy to stop the
vehicle while it is being driven and a parking brake to keep the vehicle from m\
oving while it is parked.
OPERATION
FOOT BRAKE
BR03G±06
When the brake pedal is depressed, a vacuum builds up in the booster whi\
ch amplifies the pedal force,
pressing on the piston in the master cylinder. The piston movement raises the hydraulic pressure in the
cylinder. This hydraulic pressure is then applied to each respective brake cylin\
der, and acts to press the
brake pads against the rotating discs. The resulting friction converts the ro\
tational energy to thermal ener-
gy, stopping the vehicle.
BR±2±
BRAKE SYSTEM OPERATION
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GENERAL DESCRIPTION
BR03E±06
1. Care must be taken to replace each part properly as it could affect the \
performance of the brakesystem and result in a driving hazard. Replace the parts with parts of the same part number or
equivalent.
2. It is very important to keep parts and the area clean when repairing the\
brake system.
3. If the vehicle is equipped with a mobile communication system, refer to the precaution \
in the IN section.
DESCRIPTION
BR03F±03
The service brakes consist of a foot brake which changes rotational energy to therma\
l energy to stop the
vehicle while it is being driven and a parking brake to keep the vehicle from m\
oving while it is parked.
OPERATION
FOOT BRAKE
BR03G±06
When the brake pedal is depressed, a vacuum builds up in the booster whi\
ch amplifies the pedal force,
pressing on the piston in the master cylinder. The piston movement raises the hydraulic pressure in the
cylinder. This hydraulic pressure is then applied to each respective brake cylin\
der, and acts to press the
brake pads against the rotating discs. The resulting friction converts the ro\
tational energy to thermal ener-
gy, stopping the vehicle.
BR±2±
BRAKE SYSTEM OPERATION
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SERVICE SPECIFICATIONS
SERVICE DATA
MA002±0B 








Engine 








Spark plug
Recommended spark plug
Correct electrode gap
Firing order
Valve clearance 








ND
NGK
Intake
Exhaust
\








\
PK20R11
BKR6EP11
1.1 mm (0.043 in.)
1 ± 8 ± 4 ± 3 ± 6 ± 5 ± 7 ± 2
0.15 ± 0.25 mm (0.006 ± 0.010 in.)
0.25 ± 0.35 mm (0.010 ± 0.014 in.)
 






BrakeFront and rear brakes
Pad thickness
Disc thickness
Limit
Limit (Front) (Rear)1.0 mm (0.039 in.)
30.0 mm (1.181 in.)
15.0 mm (0.591 in.)
 




Disc runout
Parking brake
Lining thickness
Drum inside diameter
()
Limit
Limit
Limit
()
0.05 mm (0.0020 in.)
1.0 mm (0.039 in.)
191 mm (7.520 in.)
 ChassisSteering linkage
Steering wheel freeplay
Limit30 mm (1.18 in.) 


gy
Ball joint
Vertical play
Limit
()
0.3 mm (0.012 in.)
MA002±0B
TORQUE SPECIFICATIONS
\
 \
Part tightened N
Vm kgf Vcm ft Vlbf
 Spark plug x Cylinder head1818013
 Front seat x Body3737527
 Front suspension crossmember x Body for nut1271,30094
  for bolt 201
,
2,050148
 Rear suspension member x Body1761,800130
 Rear suspension member rear cushion x Body3839028
±
MAINTENANCE (1UZ ± FE)MA±21
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MA04N±01
BRAKES
13. INSPECT BRAKE LINE PIPES AND HOSESHINT: Check in a well lighted area. Check the entire circum-
ference and length of the brake hoses using a mirror as re-
quired. Turn the front whe els fully right or left before checking
the front brake.
(a) Check all brake lines and hoses for: wDamage
w Wear
w Deformation
w Cracks
w Corrosion
w Leaks
w Bends
w Twists
(b) Check all clamps for tightness and connections for leakage.
(c) Check that the hoses and lines are clear of sharp edges, moving parts and the exhaust system.
(d) Check that the lines installed in grommets pass through the center of the grommets.
±
MAINTENANCE (1UZ ± FE)MA±11
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