Toyota COMPUTER-CONTROLLED SYSTEM Training Manual page 26

®
VS SIGNAL
ELECTRONIC CONTROL SYSTEM - Air Flow Mete r
There are two types of vane type air flow meter,
which differ in the nature of their electrical
circuitry . In one type, the VS voltage falls when
the air intake volume becomes large and in the
other type, the VS voltage rises when the air
intake volume becomes large .
1 Type 1
The Engine ECU has a built-in constant-voltage
circuit, which supplies a constant 5 V to the VC
terminal of the air flow meter . Consequently,
the output voltage at the VS terminal will
always indicate the exact opening angle of the
measuring plate, and therefore, the exact intake
air volume .
Fuel pump switch
Potentiomete r
FC E1 E2 VC E2
(E1) (FC)
~a~n~a~ff ;o-ts a
v
VS
OHP 12
f
2
)
Type 2
This type of air flow meter is supplied with
ba tt ery voltage from the VB terminal .
This type of air flow meter does not have a
constant voltage (5 V) supplied from the Engine
ECU, so the voltage determined by the ratio of
the resistances of the resistor between VB and
VC and the resistor between VC and E2 is input
to the Engine ECU via the VC terminal .
As a result, even when the VS voltage is
affected by fluctuations in the ba tt e ry voltage,
the Engine ECU, by executing the following
calculation, can detect the intake air volume
accurately :
Intake air volume =
VB - E2 VB - E2
(VC - E2) - (VS - E2) VC - VS
For fu
rt
her details, see Step 2, vol .
5 (EFI) .
Fuel pump switch Potentiomete
r
Voltage of ba
tt
e
ry
THA
A
VC
"
E 2
5 .0- i
Voltage (V)
VC H E 2
VS H E2
0 1
Measuring plate opening angl e
(intake air volume)
OHP 1 2
20
Voltage (V)
OHP 1 2
VBHE 2
VS H E 2
0
Measuring plate opening angl e
(intake air volume) OHP 12