0
FAIL SAFE FUNCTION
- Fail-safe Functio
n
CIRCUITRY WITH
4A-F
E
ABNORMAL SIGNALS
NECESSITY
OPERATION
ENGIN
E
• Water temp
.
If an open or sho
rt
circuit occurs in the
Values for normal operatio
n
sensor (THW)
water temperature or intake air
(standard values) are used
. Thes
e
signal circuit
ry
temperature signal circuitry the ECU
standard values differ depending o
n
assumes that the temperature is below
engine characteristics, but generally
,
• Intake air temp
.
-50°C (-58°F) or higher than 139°C (274°F)
.
a coolant temperature of 80°C
0
sensor (THA)
This results in the air-fuel ratio becoming
(176°F) and an intake ai
r
signal circuit
ry
too rich or too lean, which results in engine
temperature of 20°C (68°F) are used
.
stalling or the engine running rough
.
If the cover of the lean mixture sensor
Air-fuel ratio feedback correction i
s
becomes fouled with carbon, the ECU
stopped
.
Lean mixture sensor
cannot detect the correct oxygen
0
.
(LS) signal circuit
ry
concentration in the exhaust gas, so i
t
cannot keep the air-fuel ratio at th
e
optimal level
.
• Knock sensor
If an open or sho
rt
circuit occurs in the
The corrective retard angle is set t
o
(KNK) signal
knock signal circuit
ry
, or if trouble occurs in
the maximum value
.
circuitry
the knock control system inside the ECU
,
whether knocking occurs or not, ignitio
n
• Knock control
timing retard control will not be carried ou
t
system
by the knock control system
. This coul
d
result in damage to the engine
.
If an open or sho
rt
circuit occurs in the HAC
Values for normal operatio
n
High-altitude
sensor signal circuitry, the high-altitude
(standard values) are used
. Th
e
compensatior sensor
compensation correction will be either the
standard atmospheric pressur
e
(HAC) signal circuit
ry
maximum or the minimum value
. This will
value is 101 kPa (60 mmHg, 29
.
9
cause the engine to run poorly or reduce
in
.Hg)
.
drivability
.
Turbocharging
Abnormal increases in the turbocharging
Fail-safe stops engine by stoppin
g
pressure (PIM) signal
pressure or intake air volume, as well as
fuel injection
.
circuit
ry
other factors, may cause damage to th
e
turbocharger or engine
.
Transmission control
If trouble occurs in the microprocessor for
Torque control correction (See pag
e
signal
transmission control, the transmission will
96) by the ESA is stopped
.
not operate properly
.
If the amount of coolant supplied to the
The ignition timing is retarded by 2°
.
intercooler is insufficient, its coolin
g
Intercooler ECU (WIN)
capacity will drop
. This will cause th
e
signal circuit
ry
temperature of air taken into the cylinder
s
to rise
. As a result, the temperature of th
e
gas inside the combustion chamber wil
l
rise even higher, making it easy fo
r
knocking to occur
.
*Only for models which are equipped with the lean mixture sensor
.
146
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