Lexus SC300 / Lexus SC400. Manual - part 682

OK

NG

NG

OK

OK

NG

INSPECTION PROCEDURE

1

Check fuel pump operation.

C

OK

P

(2) Turn ignition switch ON.

(2) Using SST. connect terminals + B and FP of check

connector.

SST 09843–18020

Check that there is projection of the head of the pulsa-
tion damper screw.

Projection of the head of the pulsation damper
screw.

Go to step 3.

2

Check for open and short in harness and connector between terminals + B 

↔

  + B FP 

↔

 FP of

the check connector and fuel pump ECU (See page 

IN–27

).

Go to step 5.

Repair or replace harness or connector.

3

Check voltage or terminal + B of check connector.

C

OK

P

Turn ignition switch ON.

Measure voltage between terminal + B of check connec-
tor and body ground.

Voltage:

10 – 14 V

Check for ECU power source circuit 
(See page 

TR–124

), and check for open in harness and

connector between terminal + B of check connector and
main relay.

TR–116

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ENGINE TROUBLESHOOTING

Circuit Inspection

NG

OK

NG

OK

OK

NG

OK

NG

4

Check for open and short in harness and connector between terminal FP of check connector,
fuel pump and body ground (See page 

IN–27

).

Repair or replace fuel pump.

Repair or replace harness or connector.

5

check voltage between terminals FPC and E of fuel pump ECU connector.

C

OK

P

(2) Remove the LH quarter trim panel.

(See page 

BO–123

)

(2) Disconnect fuel pump ECU connector.

Measure voltage between terminals FPC and E of fuel
pump ECU connector when ignition switch is turned to
start.

Voltage:

4 – 6 V

Replace fuel pump ECU.

6

Check for open in harness and connector between terminal FPC of engine & ECT ECU and termi-
nal FPC of fuel pump ECU, terminal E of fuel pump ECU and body ground (See page 

IN–27

).

Repair or replace harness or connector.

7

Check for open in harness and connector between terminal DI of engine & ECT ECU and termi-
nal DI of fuel pump ECU (See page 

IN–27

).

Repair or replace harness or connector.

Check and replace engine & ECT ECU.

–

ENGINE TROUBLESHOOTING

Circuit Inspection

TR–117

Diag. Code  51

Switch Condition Signal Circuit

CIRCUIT DESCRIPTION

Neutral Start Switch Signal
The ECU uses the signals from the neutral start switch to determine whether the transmission is in park or neu-
tral, or in some other gear.
Air Conditioner Switch Signal
The ECU uses the output from the air conditioner switch to determine whether or not the air conditioner is operat-
ing so that it can increase the idling speed of the engine if necessary.
Throttle Position Sensor IDL Signal
The IDL contacts are mounted in the throttle position sensor, and detects the idle condition.

Code No.

Diagnostic Code Detecting Condition

Trouble Area

51

(1)  3 sec. or more after engine startsidle switch 

OFF (IDL1).

(2)  Neutral start switch OFF (NSW).(Shift position i

n ”R”, ”D”, ”2”or ”1” ranges).

(3)  A/C switch ON.

Throttle position sensor IDL circuit

Accelerator pedal and cable

Neutral start switch circuit

A/C switch circuit

ECU

HINT: In this circuit, diagnosis can only be made in the test mode.

DIAGNOSTIC CHART

DIAGNOSTIC CHART

See next page for DIAGNOSTIC CHART

WIRING DIAGRAM

TR–118

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ENGINE TROUBLESHOOTING

Circuit Inspection

DIAGNOSTIC CHART

DIAGNOSTIC CHART

NG (NSW)

Check for input signal.

Proceed to next circuit inspection shown
on maxtrix chart (See page 

TR–35

).

Check resistance of throttle
position sensor.

Check input circuit of A/C.

Check and repair harness or connector
between sensor and ECU.

Check for open and short in harness
and connector beteen A/C control assy.
and ECU.

Repair or replace harness or
connector.

Check and replace A/C control
assembly.

Adjust or replace throttle position
sensor (See page 

FI-73

).

See page 

TR–122

.

Check and replace ECU.

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ENGINE TROUBLESHOOTING

Circuit Inspection

TR–119