Toyota COMPUTER-CONTROLLED SYSTEM

ELECTRONIC CONTROL SYSTEM
- HAC Sensor, Vapor
Pressure Sensor,
Turbocharging Pressure Senso r
HAC (HIGH-ALTITUDE
COMPENSATION) SENSO R
The HAC sensor senses changes in the at-
mospheric pressure . Its construction and opera-
tion are the same as those of the manifold
pressure sensor (See page 17) .
This sensor can be mounted either in the Engine
ECU, or in the passenger compartment separately
from the Engine ECU . Currently, the type
mounted in the Engine ECU is used the most .
When driving at high altitudes, there is not only a
decrease in the atmospheric pressure, but also a
drop in the density of the intake air . As a result,
the air-fuel ratio deviates toward the rich side in
engines with L-type EFI (excluding hot-wire type
air flow meters) . The HAC sensor corrects for
these deviations in the air-fuel ratio .
ELECTRICAL CIRCUITR
Y
(type with sensor mounted separately )
HAC sensor
Engine ECU
TURBOCHARGING PRESSURE
SENSO R
The turbocharging pressure sensor senses the
turbocharging pressure
( intake manifold
pressure) . Its construction and operation are the
same as those of the manifold pressure sensor
(See page 17)
.
If the turbocharging pressure becomes
abnormally high, the Engine ECU cuts off the
supply of fuel to protect the engine
.
Silicon chi p
f
intake manifold pressure
OHP 3
8
(V)
5
4
3
t
Atmospheric pressure
OHP 3
8
VAPOR PRESSURE SENSO R
Basic operation and construction is the same as
that of a manifold pressure sensor or turbocharg-
ing pressure sensor
. Output characteristics differ,
however, to enable the detection of small
changes in vapor pressure .
(V )
44
5
4
3
2
1 k
0
1
-3 . 5
(-26)
Atmospheric pressur e
0 +1 .5
(0) (+11)
Pressure
kP a
(mmHg)
2
1
0 13 100 200 kPa
(100, 3
.9) (750, 29 .5) (1500, 59 .1) (mmHg, in .Hg)
Turbocharging pressure (absolute pressure)
OHP 38
ELECTRICAL CIRCUITR Y
Turbocharging
pressure sensor Engine ECU