Fail-Safe Function - Toyota COMPUTER-CONTROLLED SYSTEM Training Manual

FAIL-SAFE FUNCTION -
Fail-safe
Functio n
FAIL-SAFE FUNCTIO N
FAIL-SAFE FUNCTIO N
If the Engine ECU were to continue to control
the engine based on faulty signals, other
malfunctions could occur in the engine . To
prevent such a problem, the fail-safe function of
the ECU either relies on the data stored in
memory to allow the engine control system to
continue operating, or stops the engine if a
hazard is anticipated .
®
The following table describes the problems
which can occur when trouble occurs in the
various circuits, and the responses of the fail-
safe function .
(A circle in the "4A-FE ENGINE" column
indicates the provision of the fail-safe function
in vehicles equipped with the 4A-FE engine . )
CIRCUITRY WITH
4A-F E
ABNORMAL SIGNALS
NECESSITY OPERATION
ENGIN E
If trouble occurs in the ignition system and Fuel injection is stopped .
Ignition confirmation
ignition cannot take place (the ignitio n
't reach th e
confirmation [IGF] signal doesn
0
(IGF) signal circuit
ry
ECU), the
catalyst
could overheat due t o
misfiring .
If an open or sho
rt
circuit occurs in the
Fixed (standard) values determine d
at the time of starting by the condi -
Manifold pressure
intake manifold pressure sensor signal tion of the idle contact are used fo r
sensor (vacuum
circuit
ry
, the basic injection duration cannot the fuel injection duration and the ig- 0
sensor) (PIM) signal
be calculated, resulting in engine stalling or
nition timing making engine opera -
circuit
ry
inability to sta
rt
the engine .
tion possible .
If an open or sho
rt
circuit occurs in the air
Fixed (standard) values determine d
flow meter signal circuitry, it becomes
at the time of starting or by the
condi-
Air flow meter (VS ,
Air
impossible to detect the intake air volume tion of the idle contact are used fo r
or VG) signal cir-
and calculation of the basic injection
ig - the fuel injection duration and the ig -
cuitry
Isome engine
duration cannot be done . This results in
nition timing making engine
opera-
models only )
models
stalling or inability to sta
rt
the
tion possible .
engine .
If an open or sho
rt
circuit occurs in the
Values for normal operatio n
Thro
tt
le position (VTA) thro
tt
le position sensor signal circuit
ry
, the
(standard values) are used . (These Z
signal circuit
ry
(linear ECU detects the throttle valve as being
standard values differ depending on
0
type)
either fully open or fully closed . As a result, the engine model . )
the engine stalls or runs rough .
Since the G1 and G2 signals are used in
If only the G1 or only the G2 signal i s
cylinder identification and in detecting the
still being received, the standar d
Engine crankshaft
crankshaft angle, if an open or sho
rt
circuit
crankshaft angle can still be judge d
angle sensor (G1 and
occurs, the engine cannot be controlled, by the remaining G signal .
0
G2) signal circuit
ry
resulting in engine stalling or inability t o
sta
rt
the engine .
. 1
•2
(Continued on next page )
In previous models, the back-up mode is entered when terminal T is off . There were also some models in which
standard values are used for the intake manifold pressure signal if terminal T is connected to the El terminal .
Only for models which are equipped with the lean mixture sensor .
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