Lexus SC300 / Lexus SC400. Manual — part 870
OK
NG
OK
NG
NG
YES
7
Check each item found to be a possible cause of problem.
Check each circuit found to be a possible cause of trouble according to the results of the check in
. The
numbers in the table below show the order in which the checks should be performed.
Main oxygen sensor
signal from either
side continues at 5 V.
Main oxygen sensor
signals from both
sides continue at 5 V.
Main oxygen sensor
signals from both
sides are normal.
Possible Cause
See page
1
7
Injector circuit
3
Misfire
2
4
Valve timing
1
Air leakage
1
2
Fuel system
4
8
Characteristics deviation
in air flow meter.
2
5
Characteristics deviation
in water temp. sensor.
3
6
Characteristics deviation
in intake air temp. sensor.
Repair or replace.
8
).
Repair or replace.
9
Does malfunction disappear when a good main oxygen sensor is installed?
Replace main oxygen sensor.
Check and replace engine (& ECT) ECU.
–
ENGINE TROUBLESHOOTING
Circuit Inspection
TR–75
Diag. Code 24
Intake Air Temp. Sensor Circuit
CIRCUIT DESCRIPTION
The intake air temp. sensor is built into the air flow meter and senses the intake air temperature.
The structure of the sensor and connection to the ECU is the same as in the water temp. sensor shown on page
If the ECU records the diagnostic code ”24”, it operates the fail safe function, keeping the intake air temperature
at a constant 20
°
C (68
°
F).
Code No.
Diagnostic Code Detecting Condition
Trouble Area
24
Open or short in intake air temp. sensor circuit
for 0.5 sec. or more.
Open or short in intake air temp. sensor circuit.
Intake air temp. sensor
ECU
DIAGNOSTIC CHART
DIAGNOSTIC CHART
HINT: If diagnostic 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.
WIRING DIAGRAM
Check and replace ECU.
Replace water temp. sensor.
Check for momentary interruption
(See page
Repair or replace harness or
connector.
Check voltage of sensor.
Check resistance of sensor.
Check for open and short in harness and
connector between ECU and water temp. sensor.
–
ENGINE TROUBLESHOOTING
Circuit Inspection
TR–72
NG
OK
OK
NG
OK
NG
INSPECTION PROCEDURE
1
Check voltage between terminals THA and E2 of engine & ECT ECU connector.
C
OK
P
(2) Connect the Check Harness A.
(See page TR–30)
(2) Turn ignition switch on.
Measure voltage between terminals THA and
E2 and engine & ECT ECU connector.
Check for momentary Intertuption
(See page
).
2
Check intake air temp. sensor.
C
OK
P
Disconnect the air flow meter connector.
Measure resistance between terminals 1 and 2 of air
flow meter connector.
Resistance is within Acceptable Zone on chart.
Replace intake air temp. sensor (Replace air flow meter).
3
Check for open and short in harness and connector between engine & ECT ECU and intake air
temp. sensor (See page
).
Repair or replace harness or connector.
Check and replace engine & ECT ECU.
TR–73
–
ENGINE TROUBLESHOOTING
Circuit Inspection
Diag Code
25
Air–Fuel Ratio Lean Malfunction
Diag. Code
26
Air–Fuel Ratio Rich Malfunction
CIRCUIT DESCRIPTION
Refer to page
Code No.
Diagnostic Code Detecting Condition
Trouble Area
(1)
Main oxygen sensor voltage is 0.45 V or less (lean)
for 90 sec. under conditions (a) and (b).
(2 trip detection logic)*
(a) Coolant temp.: 60
°
C (140
°
F) or more.
(b) Engine speed: 1,500 rpm or more.
Open or short in main oxygen sensor circuit
Main oxygen sensor
Ignition system
Water temp. sensor
25
⋅
26
(2) Main oxygen sensor voltage is alternating
above and below 0.45 V at 5 times par
second or more under conditions (a) and (b).
(2 trip detection logic)*
(a) Engine speed: Idling
(b) Coolant temp.: Between 60
°
C (140
°
F)
and 95
°
C (203
°
F)
Open or short in injector circuit.
Fuel line pressure (injector blockage)
Air flow meter (air intake)
Engine ground bolt loose
Foreign object caught in valve
(3) Difference of air–fuel ratio feedback compensation
value between right and left banks is more than 10
percentage for 30 sec. or more under conditions (a)
and (b).
(2 trip detection logic)*
(a) Engine speed : 2,000 rpm or more.
(b) Coolant temp.: Between 60
°
C (140
°
F)
and 95
°
C (203
°
F)
Fuel line pressure (injector leak, blockage)
Mechanical system malfunction
(skipping teeth of timing belt)
Ignition system
*: See page
–
ENGINE TROUBLESHOOTING
Circuit Inspection
TR–74
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