1991 LEXUS SC400 Throttle Position sensor

WIRING DIAGRAM
DTC25, 26, 27TRAC Sub±Throttle Valve
CIRCUIT DESCRIPTION
DTC No.DTC Detecting ConditionTrouble Area
25
The difference between the sub±throttle sensor signal
voltage and the voltage required by the step count is 1
V or more.

Sub±throttle actuator.

Throttle body (sub±throttle valve is truck or operation is
faulty).

Sub±throttle position sensor.

Open or short in sub±throttle position sensor circuit.

ECM

TRAC ECU
26
Even when sub±throttle valve is driven to the fully open
position, input voltage at terminal VSH does not come
within range of the specifications 3 ~ 4.5 V.

Sub±throttle actuator.

Throttle body (sub±throttle valve is truck or operation is
faulty).

Sub±throttle position sensor.

Open or short in sub±throttle position sensor circuit.

ECM

TRAC ECU
27When input voltage at ECU terminal VSH is less than
the specification by about 2.5 V for 0.2 sec. or more.

Sub±throttle actuator (return spring is disconnected).

Sub±throttle position sensor.

Open or short in sub±throttle position sensor circuit.

ECM

TRAC ECU
C
OK
Hint
PRemove air cleaner and duct.
Open and close the sub±throttle valve manually and
check the condition during operation.
The valve should operate smoothly without catch-
ing.
If sub±throttle actuator, sub±throttle valve, sub±throttle
position sensor and harness are free from any defect,
ECM may be defective. If ECM is free from any defect,
TRAC ECU may be defective.
±
BRAKE SYSTEM TRACTION CONTROL SYSTEM (TRAC)BR±189
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DTC45, 46Main Throttle Position Sensor Circuit
CIRCUIT DESCRIPTION
This circuit is not directly related to the TRAC control, but as it has an i\
nfluence on TRAC control when trouble
occurs in this circuit, it is used to switch off the TRAC system as a fail safe function.
DTC No.DTC Detecting ConditionTrouble Area
45
Either of the following (1) and (2) continues for 0.12
sec.:
(1) IDL switch of main throttle position sensoris ON.
(2) Input voltage of TRAC ECU terminal VTH:1.45 V or
more.
Main throttle position sensor

Open in VTH circuit

Short in IDL1 circuit

ECM

TRAC ECU
46
Either of the following (1) or (2) continues for0.12 sec.:
(1) Input voltage of TRAC ECU terminal VTH:4.3 V or
more.
(2) Input voltage of TRAC ECU terminal VTHwhile
IDL1 switch is OFF: 0.2 V or less
Main throttle position sensor

Short in VTH circuit

ECM

TRAC ECU
BR±200±
BRAKE SYSTEM TRACTION CONTROL SYSTEM (TRAC)
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OKNG
NGOK
6Check for open and short in harness and connector between terminal VTA1 of ECM and main
throttle position sensor (See page IN±33
).
Repair or replace harness or connector.
Adjust or replace main throttle position sensor
(See page EG±333 or EG±205 ).
7Check voltage between terminal IDL1 of TRAC ECU and body ground.
C
OK
PTurn ignition switch on.
Measure voltage between terminal IDL1 of TRAC ECU
and body ground, when the main throttle valve is fully
closed and fully opened.
Check and replace TRAC ECU.
±
BRAKE SYSTEM TRACTION CONTROL SYSTEM (TRAC)BR±205
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OKNG
10Check main throttle position sensor (See page EG±609 or EG±389 ).
Adjust or replace main throttle position sensor (See
page EG±333 or EG±205).
Check and replace ECM.
±
BRAKE SYSTEM TRACTION CONTROL SYSTEM (TRAC)BR±207
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DTC47, 48Sub±Throttle Position Sensor Circuit
CIRCUIT DESCRIPTION
This sensor detects the opening angle of the sub±throttle valve and sends the appropriate signals to the ECU.
If a trouble signal is input, the ECU prohibits TRAC control.
DTC No.DTC Detecting ConditionTrouble Area
47
When any of the following (1) through (3) is detected:
(1) Deviation of 5 steps or more to the closedside of the idle step during sub±throttleinitial check.
(2) Voltage at terminal IDL2 switch is OFF evenafter sub±throttle is driven to fully closedposition during
sub±throttle initial check 4.
(3) Voltage at terminal VSH is 1.45 V or morefor at least 0.15 sec. while idle switch is ON.

Sub±throttle position sensor

Open or short in IDL2 circuit

ECM

TRAC ECU
48
Either of the following (1) or (2) continues for atleast
0.12 sec.
(1) Input voltage of TRAC ECU terminal VSH:4.3 V or more.
(2) Input voltage of TRAC ECU terminal VSHis 0.2 V or less while IDL2 switch OFF.

Sub±throttle position sensor

Open or short in VSH circuit

ECM

TRAC ECU
BR±208±
BRAKE SYSTEM TRACTION CONTROL SYSTEM (TRAC)
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OKNG
NGOK
6Check for open and short in harness and connector between terminal VTA2 of ECM and sub±
throttle position sensor (See page IN±33
)
Repair or replace harness or connector.
Adjust or replace sub±throttle position sensor
(See page EG±333 or EG±205 ).
7Check voltage between terminal IDL2 of TRAC ECU and body ground.
C
OK
PTurn ignition switch on.
Measure voltage between terminal IDL2 or TRAC ECU
connector and body ground, when the sub±throttle
valve is fully closed and fully opened.
Check and replace TRAC ECU.
±
BRAKE SYSTEM TRACTION CONTROL SYSTEM (TRAC)BR±213
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OKNG
10Check sub±throttle position sensor (See page EG±609 or EG±389 ).
Adjust or replace sub±throttle position sensor (See page
EG±333 or EG±205 ).
Check and replace ECM.
±
BRAKE SYSTEM TRACTION CONTROL SYSTEM (TRAC)BR±215
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10. REMOVE RH NO.3 TIMING BELT COVERRemove the 3 bolts, timing belt cover and 3 gaskets.
11. DISCONNECT FUEL INLET HOSE FROM LH DELIVERY PIPE
Remove the pulsation damper and 2 gaskets, and discon-
nect the fuel inlet hose from the delivery pipe.
CAUTION:
w Put a shop towel under the delivery pipe.
w Slowly loosen the union bolt.
12. D I S C O N N E C T F U E L R E T U R N H O S E F R O M F U E L
RETURN PIPE
13. DISCONNECT PCV HOSE FROM LH CYLINDER HEAD
14. REMOVE LH NO.3 TIMING BELT COVER
(a) Remove the 4 bolts.
(b) Disconnect the cord grommet from the timing belt cover, and remove the timing belt cover and 3 gaskets.
(c) Remove the cord grommet from the high±tension cord.
15. DISCONNECT HEATER WATER VALVE FROM BODY
(a) Disconnect the VSV connector.
(b) Remove the bolt holding the engine wire clamp to the water valve bracket.
(c) Remove the 2 bolts, and disconnect the water valve and bracket assembly.
16. REMOVE THROTTLE BODY
(a) Disconnect the following connectors: (1) Throttle position sensor connector
(2) w/ TRAC:
Sub±throttle position sensor connector
(3) w/ TRAC:
Sub±throttle actuator connector
EG±16
±
1UZ±FE ENGINE ENGINE MECHANICAL
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