DTC 22 Engine Coolant Temp. Sensor Circuit
CIRCUIT DESCRIPTION
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The water temperature sensor senses the engine
coolant temperature. A thermistor built in the sensor
changes the resistance value according to the en-
gine coolant temperature. The lower the engine
coolant temperature, the greater the thermistor re-
sistance value, and the higher the engine coolant
temperature, the lower the resistance value (See
Fig. 1). The engine coolant temperature sensor is
connected to the ECM (See next page). The 5V
power source voltage in the ECM is applied to the
engine coolant temperature sensor form the termi-
nal THW via a resistor R. That is, the resistor R and
the engine coolant temperature sensor are con-
nected in series. When the resistance value of the
engine coolant temperature sensor changes in ac-
cordance with changes in the engine coolant tem-
perature, the potential at the terminal THW also
changes. Based on this signal, the ECM increases
the fuel injection volume to improve drivability during
cold engine operation. If the ECM records the diag-
nostic trouble code 22, it operates the fail safe func-
tion, keeping the engine coolant temperature at a
constant 80C (176F).
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<Reference>
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Engine Coolant
Temp. C (F)
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Resistance
(k)
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Voltage
(V)
–20 (–4)
16.0
4.3
0 (32)
5.9
3.4
20 (68)
2.5
2.4
40 (104)
1.2
1.5
60 (140)
0.6
0.9
80 (176)
0.3
0.5
100 (212)
0.2
.03
Code No. Diagnostic Trouble Code Detecting Condition Trouble Area
22
Open or short in engine coolant temp. sensor circuit for
0.5 sec. or more.
Open or short in engine coolant temp. sensor
circuit
Engine coolant temp. sensor
ECM
EG–370
–ENGINE TROUBLESHOOTING CIRCUIT INSPECTION