Lexus SC300 / Lexus SC400. Manual - part 931

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

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 (See page 

TR–39

).

Check and replace ECU.

Diag. Code 43

Starter Signal Circuit

CIRCUIT DESCRIPTION

When the engine is cranked, the intake air flow is slow, so fuel vaporization is poor. A rich mixture is therefore
necessary in order to achieve good startability. While the engine is being cranked, the battery voltage is applied
to terminal STA of the ECU. The starter signal is mainly used to increase the fuel injection volume for the starting
injection control and after–start injection control.

DTC No.

DTC Detecting Condition

Trouble Area

43

No starter signal to ECU.

Open or short in starter signal circuit.

Open or short in ignition switch or starter

  relay circuit.

ECU

DIAGNOSTIC CHART

DIAGNOSTIC CHART

HINT: This diagnostic chart is based on the premise that the engine is cranked normally. If the engine is not

cranked, proceed to the matrix chart of problem symptoms on page 

TR–39

.

TR–96

–

ENGINE TROUBLESHOOTING

Circuit Inspection

INSPECTION PROCEDURE

Check output condition of diag. code 43

Setting the test mode.

6.

Turn ignition switch OFF.

7.

Connect terminals TE2 and E1 of TDCL.

8.

Turn ignition switch ON.
(Don’t start the engine)

9.

Connect terminals TE1 and E1 of TDCL.

Check if code “43” is output by the “CHECK” en-
gine warning light.

Code “43” is output.

Start the engine.
Check if the code “43” disappear.

Code “43” is not output.

Proceed to next circuit inspection shown on

matrix chart (See page 

TR–39

).

Check for open in harness and connector between engine (& ECT) ECU
and starter relay (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