Lexus SC300 / Lexus SC400. Manual — part 927
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
DIAGNOSTIC CHART
DIAGNOSTIC CHART
HINT:
•
When other codes are output in addition to 27 and 29 at the same time, check the circuits for other
codes first.
•
If diag. code 27 is displayed, check left bank sub–oxygen sensor circuit, and if 29 is displayed,
check right bank sub–oxygen sensor circuit.
WIRING DIAGRAM
Check voltage of terminals HTL2, HTR2.
Check resistance of sub–oxygen sensor heater.
Check and repair sub–oxygen sensor heater
circuit.
Check operation of sub–oxygen sensor heater.
Check and replace ECU.
Replace main oxygen sensor.
*: In this case, oxygen sensor can be
deteriorated.
Replace main oxygen sensor.*
TR–84
–
ENGINE TROUBLESHOOTING
Circuit Inspection
NG
OK
OK
NG
INSPECTION PROCEDURE
1
Disconnect the engine & ECT ECU connector.
C
OK
P
(2) Connect the Check Harness A.
(See page
(2) Disconnect engine & ECT ECU connector.
(2) Turn ignition switch on.
Measure voltage between terminals HTL2, HTR2 of en-
gine & ECT ECU connector and body ground.
Voltage:
10 – 14 V
Go to step [3].
2
Check sub–oxygen sensor heater.
C
OK
P
Disconnect sub–oxygen sensor connector.
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.
Check and repair harness or connector between
main relay and sub–oxygen sensor, sub–oxygen
sensor and engine & ECT ECU.
–
ENGINE TROUBLESHOOTING
Circuit Inspection
TR–85
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