Lexus SC300 / Lexus SC400. Manual — part 868
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.
Repair or replace harness or con-
nector.
Replace water temp. sensor.
Check voltage of sensor.
Check resistance of sensor.
Check for open and short in harness and
connector between ECU and water temp. sensor.
Check for momentary interruption
TR–69
–
ENGINE TROUBLESHOOTING
Circuit Inspection
NG
OK
OK
NG
OK
NG
INSPECTION PROCEDURE
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.
1
Check voltage between terminals THW 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 THW and E2 and
engine & ECT ECU connector.
Check for momentary interruption
(See Page
2
Check water temp. sensor.
C
OK
P
Disconnect the water temp. sensor connector.
(See page FI–99).
Measure resistance between terminals.
Resistance is within Acceptable Zone on chart.
Replace water temp. sensor.
3
Check for open and short in harness and connector between engine & ECT ECU and water temp.
sensor (See page
Repair or replace harness or connector.
Check and replace engine & ECT ECU.
–
ENGINE TROUBLESHOOTING
Circuit Inspection
TR–70
–MEMO–
TR–71
ENGINE TROUBLESHOOTING
Diag Code 25 26
Air–Fuel Ratio Lean Malfunction
Diag. Code 25, 26
Air–Fuel Ratio Rich Malfunction
CIRCUIT DESCRIPTION
Refer to page
Code No.
Diagnostic Code Detecting System
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)
*2
(a) Coolant temp.: 70
°
C (158
°
F)
or more.
(b) Engine speed: 1,500 rpm or more.
Open or short in main oxygen sensor
circuit
Main oxygen sensor
Ignition system
ECU
25
(2)
*1
Difference of air–fuel ratio feedback
compensation value between front (No.
1 3 cylinders) and rear (No. 4 6
cylinders) is more than 15 percentage
for 20 sec. or more under conditions (a)
and (b).
(2 trip detection logic)
*2
(a) Engine speed: 2,000 rpm or more.
(b) Coolant temp.: Between 60
°
C
(140
°
F) and 95
°
C (203
°
F).
Open and short in injector circuit.
Fuel line pressure (injector leak, blockage)
Mechanical system malfunction (skipping
teeth of timing belt)
Ignition system
Compression pressure (foreign object
caught in valve)
Air flow meter (air intake)
ECU
(3)
*1
Engine speed varies by more than 15
rpm over the preceding crank angle period
during a period of 20 sec. or more under
conditions (a) and (b).
(2 trip detection logic)
*2
(a) Engine speed: Idling
(b) Coolant temp.: Between 60
°
C
(140
°
F) and 95
°
C (203
°
F).
Open and short in injector circuit.
Fuel line pressure (injector leak, blockage)
Mechanical system malfunction (skipping
teeth of timing belt)
Ignition system
Compression pressure (foreign object
caught in valve)
Air flow meter (air intake)
ECU
26
*1
(1) Difference of air–fuel ratio feedback
compensation value between front (No. 1
3 cylinders) and rear (No.4 6 cylinders) is
more than 15 percentage for 20 sec. or
more under conditions (a) and (b).
(2 trip detection logic)
*2
(a) Engine speed: 2,000 rpm or more.
(b) Coolant temp.: Between 60
°
C
(140
°
F) and 95
°
C (203
°
F).
Open and short in injector circuit.
Fuel line pressure (injector leak, blockage)
Mechanical system malfunction (skipping
teeth of timing belt)
Ignition system
Compression pressure (foreign object
caught in valve)
Air flow meter (air intake)
ECU
26
1
(2) Engine speed varies by more than 15
rpm over the preceding crank angle peri-
od during a period of 20 sec. or more un-
der conditions (a) and (b).
(2 trip detection logic)
*2
(a) Engine speed: Idling
(b) Coolant temp.: Between 60
°
C
(140
°
F) and 95
°
C (203
°
F).
Open and short in injector circuit.
Fuel line pressure (injector leak, blockage)
Mechanical system malfunction (skipping
teeth of timing belt)
Ignition system
Compression pressure (foreign object
caught in valve
Air flow meter (air intake)
ECU
*1: Only for USA specification vehicles.
*2: See page
TR–70
–
ENGINE TROUBLESHOOTING
Circuit Inspection
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