Toyota COMPUTER-CONTROLLED SYSTEM User 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
.
145

Toyota COMPUTER-CONTROLLED SYSTEM Specifications

General

Brand	Toyota
Model	COMPUTER-CONTROLLED SYSTEM
Category	Automobile Accessories
Language	English