1991 LEXUS SC400 sensor

(1) Disconnect connector between center airbagsensor assembly and spiral cable.
(2) Release airbag activation prevention mecha- nism on center airbag sensor assembly side of
spiral cable connector (See page AB±60).
Check squib.
Resistance: 1 M
or higher
Repair or replace spiral cable.
Measure resistance between D+ and D± on spiral
cable side of connector between spiral cable and
steering wheel pad.
(1) Disconnect center airbag sensor assembly connector.
(2) Release airbag activation prevention mecha- nism on center airbag sensor assembly connec-
tor (See page AB±60).
Check harness between center airbag sensor assembly and spiral cable.
Resistance: 1 M
or higher
Repair or replace harness or connector
between center airbag sensor assembly and
spiral cable.
Measure resistance between D+ and D± on center
airbag sensor assembly side of connector between
center airbag sensor assembly and spiral cable.
AB±58
SRS AIRBAG
± Troubleshooting
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Check center airbag sensor assembly.
Connect center airbag sensor assembly connector.
Measure resistance between D
+, D± on center air-
bag sensor assembly side of connector between
center airbag sensor assembly and spiral cable.
Replace center airbag sensor assembly.
From the results of the above inspection, the malfunctioning part can now be\
considered normal.
To make sure of this, use the simulation method to check.
Resistance: 1 k
or higher AB±59
SRS AIRBAG
± Troubleshooting
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CHECK TERMINAL TT OUTPUT
VOLTAGE
AT00R±01
When a voltmeter is connected to the DLC1, the following
items can be checked.
1. Throttle position sensor signal
2. Brake signal
3. Shift position signal
1. VOLTMETER CONNECTION Connect the positive (+) probe of the voltmeter to terminal T
T
and the negative (±) probe to terminal E1 of the DLC2.
HINT: If a voltmeter with small internal resistance is used, the
correct voltage will not be indicated, so use a voltmeter with
an internal resistance of at least 10 k
.
2. TURN IGNITION SWITCH TO ON (DO NOT START THE
ENGINE)
3. CHECK THROTTLE POSITION SENSOR SIGNAL Check if the voltage changes from approximately 0 V to
approximately 8 V when the accelerator pedal is gradually
depressed from the fully closed position.
4. CHECK BRAKE SIGNAL (LOCK±UP CUT SIGNAL)
(a) Open the throttle valve fully to apply approximately 8 V to terminal T
T.
(b) In this condition, check terminal T
T voltage when the brake
pedal is depressed and released.
TT terminal voltage:
0 V (When brake pedal is depressed)
8 V (When brake pedal is released)
5. START ENGINE
6. CHECK SHIFT POSITION SIGNAL (VEHICLE SPEED ABOVE 60 KM/H OR 37 MPH)
Check up±shifting together with terminal T
T voltage.
HINT: Check for light shocks from up±shifting and for
changes in the tachometer.
 Gear Position Terminal TT output voltage 1st GearBelow 0.5 V 

2nd Gear1.5 ~
2 6 V
 3rd Gear3.5 ~ 4.6 V
 3rd Lock±up4.5 ~ 5.9 V
 O/D5.5 ~ 6.9 V
 O/D Lock±up6.5 ~ 7.9 V
If terminal TT output voltage check cannot be performed, per-
form the check of terminal T
T circuit on page AT±120.
±
A304E (1UZ±FE) AUTOMATIC TRANSMISSION TROUBLESHOOTINGAT±39
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\
 

\


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Trouble Area
 




O/D OFF
Light*1
Blinks
 




Memory*2
 




See
Page
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Harness or connector between No. 1 vehicle speed sensor and ECM.   
\
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No. 1 vehicle speed sensor. 

 

 
AT±78\
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Combination meter.   AT±78
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ECM   
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Harness or connector between No.4 solenoid and ECM.
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No.4 solenoid.XAT±82
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ECM
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Harness or connector between No.2 vehicle speed sensor and ECM.   
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No.2 vehicle speed sensor.   AT±86\
 
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ECM 

 

 
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Harness or connector between No.1 solenoid and ECM.
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No.1 solenoid.AT±90
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ECM
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Harness or connector between No.2 solenoid and ECM.\
 
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No.2 solenoid.AT±90
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ECM
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Harness or connector between No.3 solenoid valve and ECM.
\
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No.3 solenoid valve.XAT±94\
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ECM\
 
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Harness or connector between O/D direct clutch speed sensor and ECM.
\
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O/D direct clutch speed sensor.AT±98
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ECM
\
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±
A304E (1UZ±FE) AUTOMATIC TRANSMISSION TROUBLESHOOTINGAT±61
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*1: ªOº mark means ªO/D OFFº light blinks once every 2 seconds.\
ªXº mark means ªO/D OFFº light never
blinks.
*2: ªOº mark means the ECM memorizes the malfunction code if the ECM detects the diag. trouble \
code
detection condition.
*3: This indicates items for which ª2 trip detection logicº is use\
d. With this logic, when a logic malfunction
is first detected, the malfunction is temporarily stored in the ECM memory. If the same case is detected
again during the second drive test, this second detection causes the O/F\
OFF Light to blink.
The 2 trip repeats the same mode twice. (However, the IG switch must be turned OFF between the 1st trip
and 2nd trip.)
HINT:

If the malfunction returns to normal while a malfunction warning is being \
output, the O/D OFF indicator
light stops blinking and goes off.
However, the malfunction code is retained in memory until it is cleared from me\
mory.

If the diagnosis system outputs a malfunction code even though the O/D OFF indicator was not
blinking, there is intermittent trouble. Check all the connections in the circuit\
s corresponding to that
code.

If the vehicle speed sensors No.1 and No.2 happen to fail simultaneously\
, the ECM will neither alert
the driver by blinking the O/D OFF indicator nor record any diagnostic t\
rouble code. It will, however,
decide that the vehicle can be driven only in 1st and none of the other gears, shifting \
upwards will then
be prohibited.

Codes 46, 62, 63 and 64 are limited to short or open circuits in the electric\
al system comprised of the
solenoids, wire harnesses and connectors. The ECM is unable to detect mechanical t\
rouble (sticking,
for example) in the solenoid valves.
AT±62
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CIRCUIT INSPECTION
DTC42No. 1 Vehicle Speed Sensor Circuit
(Backup Sensor)
CIRCUIT DESCRIPTION
The No. 1 vehicle speed sensor outputs a 4±pulse signal for every revolu\
tion of the transmission output shaft.
After this signal is converted in to a more precise rectangular wave form by \
the wave form shaping circuit inside
the combination meter, it is then transmitted to the ECM.
DTC No.DTC Detecting ConditionTrouble Area
42
All conditions below are detected 500 times or ore con-
tinuously:
2 trip detection logic*
(a) No.1 vehicle speed sensor signal in 16 No 2 vehicle sensor signal
(b) Vehicle speed: 5.6 MPH (9km/h) or more for at least 4 secs. or more
(c) Park/neutral position switch: OFF (Other than P or N position)

No. 1 vehicle speed sensor.

Combination meter.

Harness or connector between No. 1 vehicle
speed sensor and ECM.

ECM
*: See page AT±62
Reference
Wave form between terminals SPD and E1 when vehicle speed is approx. 37 M\
PH (60km/h).
HINT: The greater the vehicle speed, the greater the number of SPD signals pro\
duced. AT±78
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OKNG
OKNG
INSPECTION PROCEDURE
1Check operation of speedometer.
Drive the vehicle and check if the operation of the speedometer in the c\
ombination meter is normal.
The No. 1 vehicle speed sensor is operating normally if the speedometer dis\
play is normal.C
Hint
Check speedometer circuit. See combination meter
troubleshooting on BE section.
2Check voltage between terminal SPD of ECM connector and body ground.
C
OK
P3. Connect the check harness A to the ECM (See EG section.)
4. Shift the shift lever to N position.
5. Jack up one of the rear wheels.
6. Turn ignition switch ON.
Measure voltage between terminal SPD of ECM con-
nector and body ground when he rear wheel is turned
slowly.
Voltage is generated intermittently.
Check speedometer circuit. See combination meter
troubleshooting on BE section.
Proceed to next circuit inspection shown on ma-
trix chart (See page AT±66).
However, when diag. trouble code 42 is displayed,
check and replace ECM.
AT±80±
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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±
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