FI4741
--20
0
20
40
60
80 100
(--4) (32) (68) (104) (140) (176) (212)
Temperature
˚
C (
˚
F)
R
esi
st
an
ce
k
Ω
(fig--1)
0.1
0.2
0.3
0.5
1
2
3
5
10
20
30
Acceptable
A00328
2
1
Water Temp. Sensor
Engine ECU
E4
E4 THW
E2
R
5 V
E1
G--R
LG--B
3
16
--
DIAGNOSTICS
ENGINE (1RZ--E)
DI--29
DTC 22 Water Tem p . S ensor Ci r cui t
CIRCUIT DESCRIPTION
The water temperature sensor senses the coolant temperature.
A thermistor built into the sensor changes the resistance value
according to the coolant temperature. The lower the coolant
temperature, the greater the thermistor resistance value, and
the higher the coolant temperature, the lower the thermistor re-
sistance value (See Fig.1).
The water temperature sensor is connected to the ECU (See
below). The 5 V power source voltage in the ECU is applied to
the water temperature sensor from the terminal THW via a re-
sistor R. That is, the resistor R and the water temperature sen-
sor are connected in series. When the resistance value of the
water temperature sensor changes in accordance with
changes in the coolant temperature, the potential at the termi-
nal THW also changes. Based on this signal, the ECU in-
creases the fuel injection volume to improve driveability during
cold engine operation. If the ECU detects the diagnostic trouble
code 22, it operates the fail safe function in which the engine
coolant temperature is assumed to be 80
˚
C (170
˚
F).
DTC No.
Detection Item
Trouble Area
22
Open or short in water temp. sensor circuit for 0.5 sec. or more
S
Open or short in water temp. sensor circuit
S
Water temp. sensor
S
Engine ECU
WIRING DIAGRAM
DI1HQ--01
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