Lexus SC300 / Lexus SC400. Service manual — part 673
OK
NG
OK
NG
NO
YES
7
Check each item found to be a possible cause of problem.
Check each ciruit found to be a possible cause of trouble according to the results of the check in 1. The
numbers in the table below show the order in the which the checks should be performed.
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–80
–MEMO–
TR–81
ENGINE TROUBLESHOOTING
Diag. Code 27, 29
Sub–Oxygen Sensor Circuit
CIRCUIT DESCRIPTION
The sub–oxygen sensor is installed on the exhaust pipe. Its construction and operation is the same as the main
oxygen sensor on page
.
Code No.
Diagnostic Code Detecting Condition
Trouble Area
(1) Open or short in heater circuit of sub–oxygen
sensor for 0.5 sec. or more.
Open or short in heater circuit of sub–oxygen
sensor
Sub–oxygen sensor heater.
ECU
27
29
(2) Main oxygen sensor signal is 0.45 V or more and
sub–oxygen sensor signal is 0.45 V or less
under sonditions (a) and (b).
(2 trip detection logic) *
(a) Coolant temp.: 80
°
C (176
°
F) or more.
(b) Accel. pedal: Fully depressed for 2 sec. or
more.
Open or short in sub–oxygen sensor circuit.
Sub–oxygen sensor
ECU
*: See
.
HINT:
Diag. code 27 is for the left bank sub–oxygen sensor circuit.
Diag. code 29 is for the right bank sub–oxygen sensor circuit.
TR–82
–
ENGINE TROUBLESHOOTING
Circuit Inspection
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.
Malfunction: Open or Short in Sub–Oxygen Sensor
Start engine and warm up.
After engine is warmed up, let it idle for 3 min.
With the A/C ON and the transmission in D range (O/D OFF), drive at 40 –60 mph (64–96
km/h) for 6 min.
After the driving in , stop the vehicle.
Once the vehicle is stopped, within the next minute apply acceleration with the throttle
fully open for 4 sec.
HINT: If a malfunction exists, the ”CHECK” engine warning light will light up after full acceleration
for 4 sec.
NOTICE:
If the conditions in this test are not strictly followed, detection of the malfunction
will not be possible.
–
ENGINE TROUBLESHOOTING
Circuit Inspection
TR–83
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