1991 LEXUS SC300 code 32

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 c\
onfirming that diag. code is no longer detected.
Malfunction: Open or Short in Main Oxygen Sensor

Initiate test mode (See page TR±12).
Start engine and warm up.
After engine is warmed up, let it idle for 3 min.
Perform quick racing to 4,000 rpm three times by accelerator pedal.
After performing the racing in (4), perform racing at 2,000 rpm for 90\
sec.
HINT: If a malfunction exists, the ºCHECKº engine warning light will light up after 90 sec. from the start of racing.
NOTICE: If the conditions in this test are not strictly followed, detection of t\
he malfunction will not be possible.
TR±75±
ENGINE TROUBLESHOOTING Circuit Inspection
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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 co\
nfirming that diag. codeis no longer detected.
Malfunction: Open or Short in Injector circuit, Injector Leak or Blockage, Loose E/G Earth Bolt.

Initiate test mode (See page TR±12).
Start engine and warm up.
After engine is warmed up, let it idle for 5 min.
(After the engine is started, do not depress the accelerator pedal.)
\bIf the malfunction is not detected during idling, perform racing without a\
ny load at approx.
2,000 rpm for 30 sec.
HINT: If a malfunction exists, the ºCHECKº engine warning light will light up during the 5 min. idling
period or within 30 sec. of starting racing.
NOTICE: If the conditions in this test are not strictly followed, detection of the\
malfunction will not be possible.
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ENGINE TROUBLESHOOTING Circuit InspectionTR±76
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Diag. Code 27, 29Sub±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 TR±62.
Code No.Diagnostic Code Detecting ConditionTrouble 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 5C (176 5F) 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 page TR±21.
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
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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 co\
nfirming that diag. codeis no longer detected.
Malfunction: Open or Short in Sub±Oxygen Sensor

Initiate test mode (See page TR±12).
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 w\
ith the throttle
fully open for 4 sec.
HINT: If a malfunction exists, the ºCHECKº 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.
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ENGINE TROUBLESHOOTING Circuit InspectionTR±83
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DIAGNOSTIC CHART
DIAGNOSTIC
CHART
HINT:
wWhen other codes are output in addition to 27 and 29 at the same time, check the ci\
rcuits for other
codes first.
w If diag. code 27 is displayed, check left bank sub±oxygen sensor circ\
uit, 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
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Diag. Code 31Air Flow Meter Circuit
CIRCUIT DESCRIPTION
As shown in the figure at right, when a pillar (Vortex
generating body) is placed in the path of a uniform flow,
vortices called Karman±Vortex are generated down-
stream of the object. Using this principle, a vortex gen-
erator is placed inside the air flow meter. By measuring
the frequency of the vortices generated, the ECU can
determine the volume of air flowing through the air flow
meter. The vortices are detected by their exerting pres-
sure on thin metal foil (mirror) surfaces and a light emit-
ting element and light receptor (LED and photo transis-
tor) positioned opposite the mirror which senses the
vibrations in the mirror optically. The ECU uses these
signals mainly for calculation of the basic injection vol-
ume and the basic ignition advance angle.
If the ECU records diagnostic code º31º, it enters fail safe mode \
(See page TR±22).
TR±88
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ENGINE TROUBLESHOOTING Circuit Inspection
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DIAGNOSTIC CHART
DIAGNOSTIC
CHART
WIRING DIAGRAM
Check and replace ECU.Replace air flow meter. Check and replace ECU.
Check voltage of air flow meter power source. Check voltage terminal KS of ECU.
Check for open and short in harness and
connector between air flow meter and ECU. Check voltage of terminal KS.
Repair or repolace harness or
connector
When diag. code 31 is displayed,
check and replace ECU.
±
ENGINE TROUBLESHOOTING Circuit InspectionTR±89
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NGOK
OKNG
INSPECTION PROCEDURE
1Check voltage between terminals KS and E1 of engine & ECT ECU connector.
C
OK
PConnect the check harness A.
(See page TR±30)
Measure voltage between terminals KS and E1 of en-
gine & ECT ECU connector while engine is cranked.
Voltage: 2.0 ± 4.0 V (Neither 0 V nor 5 V)
When diag. code 31 is displayed, check and replace en-
gine & ECT ECU.
2Check for open and short in harness and connector between engine & ECT ECU and air flow
meter (See page IN±27).
Repair or replace harness or connector.
TR±90
±
ENGINE TROUBLESHOOTING Circuit Inspection
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