Lexus SC300 / Lexus SC400. Manual — part 939
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
).
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
(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
).
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
).
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
–
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
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
).
See page
Check and replace ECU.
–
ENGINE TROUBLESHOOTING
Circuit Inspection
TR–119
OK
NG
OK
NG
INSPECTION PROCEDURE
1
Check output condition of diag. code 51.
C
OK
Hint
P
Setting the test mode.
(2) Turn ignition switch OFF.
(2) Connect terminals TE2 and E1 and TDCL.
(2) Turn ignition switch ON.
(For checking terminal A/C, start the engine.)
(2) Connect terminals TE1 and E1 of TDCL.
Check if code “51” is output by the “CHECK” engine
warning light.
*: Before the STA signal is input (ST is not ON),
diagnostic code 43 is also output.
Diag. code 42 is output with vehicle speed 5 km/h (3
mph) or below
IDL1 . Go to step 2 NSW ... Go to page
A/C . . Go to step 3
Proceed to next circuit inspection shown on
maxtrix chart (See page
2
Check throttle position sensor.
C
OK
P
Disconnect throttle position sensor connector.
Measure resistance between terminals IDL1 and E2 of
throttle position sensor connector.
Adjust or replace throttle position sensor
See page
Check and repair harness or connector between
engine & ECT ECU and throttle position sensor.
TR–120
–
ENGINE TROUBLESHOOTING
Circuit Inspection
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