Toyota COMPUTER-CONTROLLED SYSTEM - Page 117

ISC - Functions of Engine EC U
FUNCTIONS OF ENGINE EC
U
1 . STEPPER MOTOR
TYPE ISC VALV E
This type of ISC valve is connected to the Engine opening angle and vehicle speed signals that the
ECU as shown in the following diagram
. Target engine is idling, it switches on Tr, to Tr4, in that
idling speeds for each coolant temperature and order, in accordance with the output of those
air conditioner operating state are stored in the signals
. This sends current to the ISC valve coil,
ECU's memory
. until the target idling speed is reached
.
When the ECU judges from the throttle valv
e
Engine ECU
BAT T
Battery
EFI main relayr- Microprocesso
r
fl B+ *
IIbII x -- I
Ignition switch
-RE L
IGSW
E1
Main relay
control circui
t
\ 1
* Some models onl
y
STARTING SET-U P
When the engine is stopped (
no NE signal to the
ECU), the ISC valve opens fully (
to the 125th
step) to improve sta rt
ability when the engine is
resta rt ed .
• Main Relay (ISC Valve Set-up) Contro l
The supply of power to the ECU and ISC
valve must be continued for a few moments,
even after the ignition switch is turned off,
in order to allow the ISC valve to be set up
(fully opened) for the next engine start-up
.
Therefore, the ECU outputs 12 V from the M-
REL terminal until the ISC valve is set up, in
order to keep the main relay on
. Once set-up
is complete, it cuts off the flow of current to
the main relay coil .
OHP 74
CONDITIONS
CURRENT T O
MAIN RELA Y
Ignition switch on
O N
Ignition switch off
O N
(ISC valve set-up is I
complete)
OF F
RELEVANT SIGNAL
-*Engine speed (NE
)
/- NOT E
Stepper motor type ISC valves will enter a hold
state when the power is interrupted . As a
result, they are stopped at the position where
they were when the power was interrupted .
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