Lexus SC300 / Lexus SC400. Service manual — part 926
CIRCUIT DESCRIPTION (Cont’d)
DIAGNOSIS CODE DETECTION DRIVING PATTERN
Purpose of the driving pattern.
(a) To simulate diag. code detecting condition after diag. code is recorded.
(b) To check that the malfunction is corrected when the repair is completed confirming that diag. code is
no longer detected.
Disconnect the EFI fuse (15 A) for 10 sec. or more, with IG switch OFF.
Initiate test mode (Connect terminal TE2 and E1 of check connector with IG switch
OFF).
Start the engine and warm up with all ACC switch OFF.
After the engine is warmed up, let it drive at 50 55 mph (80 88 km/h) for 10 min. or
more.
After driving, stop at a safe place and perform idling for 2 min. or less.
After performing the idling in , perform acceleration to 60 mph (96 km/h) with the
throttle valve fully open.
HINT: If a malfunction exists, the ”CHECK” engine warning light will light up during
step
.
NOTICE: If the conditions in this test are not strictly followed, detection of the
malfunction will not be possible.
Malfunction: Open or Short in Sub–Oxygen Sensor
–
ENGINE TROUBLESHOOTING
Circuit Inspection
TR–77
DIAGNOSTIC CHART
HINT: When other codes are output in addition to 27 at the same time, check the circuits for other
codes first.
WIRING DIAGRAM
Check voltage between terminal HT.
Check resistance of sub–oxygen sensor
heater.
Check for open and short in harness and
connector between EFI main relay and ECU.
Check and replace ECU.
Check operation of sub–oxygen sensor
heater.
Check and replace ECU.
Replace sub–oxygen sensor.
Repair or replace harness or
connector.
Replace sub–oxygen sensor.*
*: In this case, oxygen sensor can be
deteriorated.
TR–78
–
ENGINE TROUBLESHOOTING
Circuit Inspection
NG
OK
OK
NG
INSPECTION PROCEDURE
1
Check voltage between terminal HT of engine (&ECT) ECU connector and body ground.
C
OK
P
1.
Connect the Check Harness A. (See page
).
2.
Turn ignition switch on.
Measure voltage between terminal HT of engine (&
ECT) ECU connector and body ground.
Voltage:
10 – 14 V
Go to step
.
2
Check sub–oxygen sensor heater.
C
OK
P
Disconnect sub–oxygen sensor connector.
(See page
).
Measure resistance between terminals 1 and 2 of
sub–oxygen sensor connector.
Resistance:
5.1 – 6.3
20
°
C (68
°
F)
Replace sub–oxygen sensor.
–
ENGINE TROUBLESHOOTING
Circuit Inspection
TR–79
OK
NG
NG
OK
3
Check for open and short in harness and connector between EFI main relay and engine (& ECT)
ECU (See page
Repair or replace harness or connector.
Check and replace engine (& ECT) ECU.
4
Check voltage between terminal HT of engine (& ECT) ECU connector and body ground.
C
OK
P
Warm up engine to normal operating temperature.
Measure voltage between terminal HT of engine (&
ECT) ECU connector and body ground, when engine is
idling and racing at 3,500 rpm.
Replace sub–oxygen sensor.*
*: In this case, oxygen sensor can be deteriorated.
Check and replace engine (& ECT) ECU.
TR–80
–
ENGINE TROUBLESHOOTING
Circuit Inspection
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