Toyota COMPUTER-CONTROLLED SYSTEM Training Manual page 66

~
REFERENCE
Circuit-opening Relay
EFI - Fuel System
The resistor R and the capacitor C in the
circuit-opening relay are for the purpose of
preventing the relay contacts from opening
when current stops flowing in coil L2 due to
electrical noise ( fuel pumps controlled by the
ECU) or to sudden drops in the intake ai r
ON-OFF CONTROL (BY FUEL PUMP
SWITCH) *
~) Engine crankin g
When the engine is cranking, current flows from
the IG terminal of the ignition switch to the Li
coil of the EFI main relay, turning the relay on .
Current also flows from the ST terminal of the
ignition switch to the La coil of the circuit-
opening relay, turning it on to operate the fuel
pump . After the engine starts, the cylinders
begin drawing in air, causing the measuring
plate inside the air flow meter to open . This
turns on the fuel pump switch, which is
connected to the measuring plate, and current
flows to the Lz coil of the circuit-opening relay .
~2 Engine sta
rt
e d
After the engine sta rt s and the ignition switch is
turned from START back to ON, current flowing
volume ( fuel pumps controlled by fuel pump
switch) .
They also serve to prevent sparks from being
generated at the relay contacts .
On some recent models, an L3 coil is not
provided in the circuit-opening relay .
to the La coil of the circuit-opening relay is cut
off. However, current continues to flow to the Ls
coil, while the engine is running, due to the fuel
pump switch inside the air flow meter being on .
As a result, the circuit-opening relay stays on,
allowing the fuel pump to continue operating .
~3 Engine stopped
When the engine stops, the measuring plate
completely closes and the fuel pump switch is
turned off . This cuts off the flow of current to
the Ls coil of the circuit-opening relay . As a
result, the circuit-opening relay goes off and the
fuel pump stops operating .
L-type EFI with vane type air flow meter .
Check (m p T~
Circuit-opening rela y
connecto r
Battery
2P fuel pump check connector (some
engines only)
-
IN
OHP 4 6
56