Lexus SC300 / Lexus SC400. Manual — part 937
OK
NG
OK
NG
6
Check resistance of EGR gas temp. sensor.
C
OK
P
Disconnect EGR gas temp. sensor connector
(See page
Measure resistance between terminals of EGR gas
temp. sensor connector.
Resistance:
69 – 89 k
at 50
C (122
F)
12 – 15 k
at 100
C (212
F)
2 – 4 k
at 150
C (302
F)
Replace EGR gas temp. sensor.
7
Check for open and short in harness and connector between EGR gas temp. sensor and engine
& ECT ECU (See
Repair or replace harness or connector.
Check and replace engine & ECT ECU.
–
ENGINE TROUBLESHOOTING
Circuit Inspection
TR–113
WIRING DIAGRAM
Diag. Code 78
Fuel Pump Control Circuit
CIRCUIT DESCRIPTION
The fuel pump speed is controlled at two steps (high speed, low speed) by the condition of the engine (starting, light load,
heavy load), when the engine starts (STA ON), the engine (& ECT) ECU sends a Hi signal to the fuel pump ECU (FPC termi-
nal).
The fuel pump ECU then outputs Hi voltage (battery voltage) to the fuel pump so that the fuel pump operates at high speed.
After the engine starts, during idling or light loads, the engine (& ECT) ECU outputs a High Low signal to the fuel pump ECU,
the fuel pump ECU outputs Lo battery voltage (about 9V) to the fuel pump and causes the fuel pump to operate at low speed.
If the intake air volume increases (high engine load), the engine (& ECT) ECU sends a Hi signal to the fuel pump ECU and
causes the fuel pump to operate at high speed.
DTC No.
DTC Detecting Condition
Trouble Area
(1) Open or short in fuel pump circuit for 1 sec. or more with en-
gine speed 1,000 rpm or less.
(2 trip detection logic)*
Open or short in fuel pump ECU circuit.
78
(2) Open in input circuit of fuel pump ECU (FPC) with engine
speed 1,000 rpm or less.
(2 trip detection logic)*
Fuel pump ECU
Engine (& ECT) ECU power source circuit.
Fuel pump
(3) Open or short in diagnostic signal line (DI) of fuel pump
ECU with engine speed 1,000 rpm or less.
(2 trip detection logic)*
Engine (& ECT) ECU
*: See page
TR–110
–
ENGINE TROUBLESHOOTING
Circuit Inspection
DIAGNOSTIC CHART
Check fuel pump operation.
Check for open and short in harness and
connector between check connector and
fuel pump ECU.
Repair or replace harness or connector.
Check voltage of terminal +B of check
connector.
Check for open and short in harness and
connector between check connector and
fuel pump.
Repair or replace harness or connector.
Check voltage of terminal FPC.
Check for open and short in harness and
connector between ECU and fuel pump
ECU. ((FPC)
Check for open and short in harness and
connector between ECU and fuel pump
ECU. (DI)
Check and replace ECU.
Check for ECU power source
circuit.
Repair or replace fuel pump.
Replace fuel pump ECU.
Repair or replace harness or
connector.
Repair or replace harness or
connector.
–
ENGINE TROUBLESHOOTING
Circuit Inspection
TR–111
OK
NG
NG
OK
OK
NG
INSPECTION PROCEDURE
1
Check fuel pump operation.
C
OK
P
1.
Turn ignition switch ON.
2.
Using SST, connect terminals +B and FP of check
connector.
SST 09843–18020
Check that there is pressure in the hose from the fuel
filter.
Fuel pressure can be felt.
Go to step
.
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
).
Go to step
.
Repair or replace harness or connector.
3
Check voltage of 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
),
and check for open in harness and connector between
terminal +B of check connector and main relay.
TR–112
–
ENGINE TROUBLESHOOTING
Circuit Inspection
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