Toyota COMPUTER-CONTROLLED SYSTEM Training Manual page 154

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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
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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
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.
(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 .
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