1991 LEXUS SC400 Service Repair Manual

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Page 3505 of 4087

$LEXUS SC400 1991 Service Repair Manual OKNG NGOK 3Disconnect air flow meter connector and check voltage between terminals \ KS and E1 of engine & ECT ECU. C OK PDiconnect the air flow meter connector. Turn ignition switch on. Measure volt$

Page 3506 of 4087

$LEXUS SC400 1991 Service Repair Manual Diag. Code 35High Altitude Compensator Sensor (HAC Sensor) Circuit CIRCUIT DESCRIPTION The HAC sensor is built into the ECU. This is a semiconductor pressure sens\ or with properties which cause i$

Page 3507 of 4087

LEXUS SC400 1991 Service Repair Manual
±MEMO±
ENGINE TROUBLESHOOTINGTR±93
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Page 3508 of 4087

LEXUS SC400 1991 Service Repair Manual
Diag. Code 41, 47(Sub±) Throttle Position Sensor Circuit
CIRCUIT DESCRIPTION
The throttle position sensor is mounted in the throttle body
and detects the throttle valve opening angle. When the
thr

Diag. Code 41, 47(Sub±) Throttle Position Sensor Circuit
CIRCUIT DESCRIPTION
The throttle position sensor is mounted in the throttle body
and detects the throttle valve opening angle. When the
throttle valve is fully closed, the IDL contacts in the throttle
position sensor are on, so the voltage at the terminal IDL of
the ECU become 0 V. At this time, a voltage of approximately
0.7 V is applied to the terminal VTA of the ECU. When the
throttle valve is opened, the IDL contacts go off and thus the
power source voltage of approximately 12 V in the ECU is ap-
plied to the terminal IDL of the ECU. The voltage applied to
the terminal VTA of the ECU increases in proportion to the
opening angle of the throttle valve and becomes approxi-
mately 3.5±5.0 V when the throttle valve is fully opened. The
ECU judges the vehicle driving conditions from these signals
input from the terminals VTA and IDL, and uses them as one
of the conditions for deciding the air±fuel ratio correction,
power increase correction and fuel±cut control etc. The sub±
throttle position sensor is built and operates in the same way
as the main throttle position sensor. This sensor is used for
traction control. The sub±throttle valve is opened and closed
by the sub±throttle actuator according to signals from the
TRAC ECU to control the engine output.
Code No.Diagnostic Code Detecting ConditionTrouble Area
41
(1) Open or short in throttle position sensor circuit(VTA1) for 0.5 sec. or more.Open or short in throttle position sensor cir-
cuit.
41(2) IDL1 contact is ON and VTA1 output exceeds 1.5 V for 0.5 sec. or more.Throttle position sensor
ECU
47
(1) Open or short in sub±throttle position sensor
circuit (VTA2) for 0.5 sec. or more.Open or short in sub±throttle position sensor
circuit.
47(2) IDL2 contact is ON and VTA2 output exceeds 1.5 V for 0.5 sec. or more.Sub±throttle position sensor
ECU
HINT:
Diag. code 41 is for the throttle position sensor circuit.
Diag. code 47 is for the sub±throttle position sensor circuit.
w When the connector for the (sub±) throttle position sensor is disconnec\
ted, diagnostic code 41 or 47 is not
displayed. Diagnostic code 41 or 47 is displayed only when there is an open or short in the VTA signal circuit
of the (sub±) throttle position sensor.
w Signals from the (sub±) throttle position sensor are also input to the TRAC ECU, So when a malfu\
nction
occurs on the TRAC side, code 41 or 47 may be displayed.
TR±94
±
ENGINE TROUBLESHOOTING Circuit Inspection
WhereEverybodyKnowsYourName

Page 3509 of 4087

$LEXUS SC400 1991 Service Repair Manual DIAGNOSTIC CHART DIAGNOSTIC CHART HINT: wIf diag. code 41 is displayed, check throttle position sensor circuit; if d\ iag. code 47 is displayed, check sub±throttle position sensor circuit. w If dia$

Page 3510 of 4087

$LEXUS SC400 1991 Service Repair Manual NGOK INSPECTION PROCEDURE HINT: wIf diag. code 41 is displayed, check throttle position sensor circuit. If \ diag. code 47 is displayed, check sub±throttle position sensor circuit. w If diag. codes$

Page 3511 of 4087

LEXUS SC400 1991 Service Repair Manual
OKNG
OKNG
2Check (sub±) throttle position sensor.
C
OK
Hint
P(2) Remove intake air duct.
(2) Disconnect (sub±) throttle position sensor connec-tor.
Measure resistance between terminals 3, 2, and 1

Page 3512 of 4087

LEXUS SC400 1991 Service Repair Manual
WIRING DIAGRAM
Check for the test mode.
Check for open in harness and connector
between ECU and relay.Repair or replace harness or
connector.
Proceed to next circuit inspection shown
on matrix chart

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