Lexus SC300 / Lexus SC400. Manual — part 875
NG
OK
3
Check voltage between terminals HTL2, HTR2 of engine & ECT ECU connector and body
ground.
C
OK
Hint
P
(2) Connect engine & ECT ECU connector.
(2) Warm up engine to normal operating temperature.
Measure voltage between terminals HTL2, HTR2 of en-
gine & ECT ECU connector and body ground, when en-
gine is idling and racing at 4,000 rpm.
In the 4,000 rpm racing check , continue engine racing
at 4,000 prm for approx. 20 seconds or more.
Replace sub–oxygen sensor.*
*: In this case, oxygen sensor can be deteriorated.
Check and replace engine & ECT ECU.
TR–86
–
ENGINE TROUBLESHOOTING
Circuit Inspection
–MEMO–
ENGINE TROUBLESHOOTING
TR–87
Diag. Code 35
High Altitude Compensator Sensor
(HAC Sensor) Circuit
CIRCUIT DESCRIPTION
The HAC sensor is built into the ECU. This is a semiconductor pressure sensor with properties which
cause its electrical resistance to change when stress is applied to the sensor’s crystal (silicon) (piezo-
electric effect). This sensor is used to detect the atmospheric (absolute) pressure and outputs corre-
sponding electrical signals. Fluctuations in the air pressure cause changes in the intake air density,
which can cause deviations in the air–fuel ratio. The signals from HAC sensor are used to make correc-
tions for these fluctuations. If the ECU records diagnostic code ”35”, the fail safe function operates and
the atmospheric pressure is set at a constant 101.3 kPa (760 mmHg, 29.92 in.Hg).
Code No.
Diagnostic Code Detecting Condition
Trouble Area
35
Open or short in HAC sensor circuit for
0.5 sec. or more.
ECU
DIAGNOSTIC CHART
Are there any other codes (besides Code 16)
being output?
Replace engine (& ECT) ECU.
Go to relevant diag. code chart.
TR–86
–
ENGINE TROUBLESHOOTING
Circuit Inspection
Diag. Code 31
Air 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 ”31”, it enters fail safe mode (See page
TR–88
–
ENGINE TROUBLESHOOTING
Circuit Inspection
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