Lexus SC300 / Lexus SC400. Manual — part 677

NG

OK

INSPECTION PROCEDURE

HINT:

•

If diag. code 41 is displayed, check throttle position sensor circuit. If diag. code 47 is displayed, check
sub–throttle position sensor circuit.

•

If diag. codes ”22” (water temperature sensor circuit), ”24” (intake air temperature sensor circuit) and ”41”
(throttle position sensor circuit) are output simultaneously, E2 (sensor ground) may be open.

#

Check voltage between terminals VTA1, 2, IDL1, 2 and E2 of engine & ECT ECU connector.

C

OK

Hint

P

(2) Connect the Check Harness A.

(See page TR–30).

(2) Turn ignition switch on.

(2) For sub–throttle position sensor, remove intake air

duct and disconnect sub–throttle valve step motor
connector.

Measure voltage between terminals VTA1, 2, IDL1, 2
and E2 of engine & ECT ECU connector when the
(sub–) throttle valve is opened gradually from the closed
condition.

The voltage should increase steadily in proportion to the
throttle valve opening angle.

Check for Momentary interruption
(See page

TR–23

).

Go to step [2].

TR–96

–

ENGINE TROUBLESHOOTING

Circuit Inspection

OK

NG

OK

NG

2

Check (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 of
(sub–) throttle position sensor connector when the
throttle valve is opened gradually from the closed condi-
tion.

Resistance between terminals 3 and 1 should increase
gradually in accordance with the throttle valve opening
angle.

Adjust or replace (sub–) throttle position sensor
(See page

FI–73

).

3

Check for open and short in harness and connector between engine & ECT ECU and
(sub–) throttle position sensor (See page

IN–27

).

Repair or replace harness or connector.

Check and replace engine & ECT ECU.

–

ENGINE TROUBLESHOOTING

Circuit Inspection

TR–97

Diag. Code 42

Vehicle Speed Sensor Signal Circuit

CIRCUIT DESCRIPTION

The No. 1 speed sensor outputs a 20–pulse signal for every revolution of the rotor shaft, which is rotated by
the transmission output shaft via the driven gear. This signal is converted in the combination meter to 4–pulse
signal by the pulse conversion circuit and then sent to the Engine & ECT ECU. The ECU determines the vehicle
speed based on the frequency of these pulse signals.

Code No.

Diagnostic Code Detecting Condition

Trouble Area

42

All conditions below are detected continuously for 8
sec. or more.

(a) Vehicle speed signal: 0 km/h (0 mph)

(b) Engine speed: 1,500 rpm or more

(c) Neutral start switch (NSW): OFF

No. 1 speed sensor.

Combination meter.

Open or short in No. 1 speed sensor circuit.

ECU

HINT: In test mode, diag. code 42 is output when vehicle speed is 5 km/h (3 mph) or below.

DIAGNOSTIC CHART

DIAGNOSTIC CHART

Check operation of speedometer.

Check voltage of terminal SPD.

Check and replace ECU.

Check speedometer circuit.
(See page

BE–131

).

Check speedometer circuit.
(See page

BE–131

).

WIRING DIAGRAM

TR–98

–

ENGINE TROUBLESHOOTING

Circuit Inspection

OK

NG

OK

NG

1

Check operation of speedometer.

Drive the vehicle and check if the operation of the speedometer in the combination meter is normal.

The No. 1 speed sensor is operating normally if the speedometer display is normal.

C

Hint

Check speedometer circuit. See combination meter trou-
bleshooting on page

BE–131

.

2

Check voltage between terminal SPD of engine & ECT ECU connector and body ground.

C

OK

P

(2) Shift the shift level to N range.

(2) Jack up a read wheel on one side.

(2) Connect the Check Harness A.

(See page

TR–30

)

(2) Turn ignition switch on.

Measure voltage between terminal SPD of engine &
ECT ECU connector and body ground when the wheel
is turned slowly.

Voltage is generated intermittently.

Check speedometer circuit. See combination meter trou-
bleshooting on page

BE–131

.

Check and replace engine & ECT ECU.

–

ENGINE TROUBLESHOOTING

Circuit Inspection

TR–99