BACK-UP FUNCTION
- Back-up functio
n
BACK-UP FUNCTIO
N
BACK-UP FUNCTIO
N
The back-up function is a system which switches
to the back-up IC for fixed
signal
control* if
trouble occurs with the microprocessor inside
the ECU
. This allows the vehicle to continue
operating, though it
assures
the continuation o
f
l
Engine ECU
Back-up
I
C
STA
:
:
:=
IDL
Malfunction
monitor
only basic functions
; normal performance cannot
be maintained
.
*Control by the back-up IC in which the IC uses
preprogrammed data to control the ignition
timing and fuel injection duration
.
Microprocesso
r
*Injectio
n
signal
0-
O
Various
signal
s
*Ignitio
n
timing
signal
IGT
X
n
k
1
o,zo
-&-
OPERATIO
N
The ECU switches to the back-up mode when the
microprocessor stops outputting the ignition tim-
ing (IGT) signal
.
When the ECU switches to the back-up mode, fix-
ed values* are substituted for fuel injection dura-
tion and ignition timing and as a result, engine
operation is maintained . The back-up IC sets the
fixed values* according to the condition of the
STA signal and the idle contact
. At the same time,
it lights the "CHECK ENGINE" lamp to inform the
driver
.
(Codes are not output in this case, however
.
)
*These values differ depending on the engine
model
.
In addition, on some recent models, when the
back-up mode is entered, the engine is stopped by
interrupting fuel injection
.
/__
NOT
E
In the case of conventional D-type EFI, when
the intake manifold pressure (PIM) signal was
open or short circuited, the microprocessor for-
cibly switched to the back-up mode by interrup-
ting the ignition timing (IGT) signal
. More
recently, however, fixed values for fuel injec-
tion duration and ignition timing are contained
within the microprocessor
. As a result, when a
problem like that described above occurs, the
microprocessor controls the engine with a fail
safe function
.
147
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