Back-Up Function - Toyota COMPUTER-CONTROLLED SYSTEM Training Manual

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 IC
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
*Injection
signal
0-
O
Various
signal s
*Ignitio n
timing
signal
IGT
Xn
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