Dtc23 - Ect Sensor System Fault - Isuzu 4HL1 Workshop Manual

DTC23 - ECT Sensor System Fault

Circuit Description
The ECT (engine coolant temperature) sensor consists
of thermistor and alters the resistance in response to
temperature change.
temperature provides smaller resistance while lower
temperature provides larger resistance. The ECM
supplies 5 V to the ECT sensor via pull-up resistance
and calculates the engine coolant temperature from the
change in voltage and uses it in fuel injection control,
EGR control, and other control tasks. The voltage is
decreased when the
temperature is high) while increased when the
resistance is large (the temperature is low).
DTC23 will be set when the signal voltage is
excessively high or low.
Major Faulty Event
• Poor startability under cold weather conditions
• Poor driveability
• Prolonged warm-up time
Conditions for Setting the DTC
The ECT sensor output voltage deviates from the
range between 0.1 V and 4.9 V for at least 3 seconds.
Action Taken When the DTC Sets
• After the DTC is set, the ECM will illuminate the
CHECK ENGINE lamp (MIL).
49 46
ECT
Sensor
Higher engine coolant
resistance is small
ECM
(Engine
Control
Module)
48
FT
Sensor
• The ECM controls the powertrain using the set
engine coolant temperature (normal running
phase: 110°C, startup phase: –20°C).
• EGR and warm-up systems are disabled.
Conditions for Clearing MIL/DTC
When the system fails and the DTC is stored to the
ECM, even repairing the faulty portion will not clear the
DTC from the memory. To clear the DTC, conduct the
following steps.
(the
1. Turn off the idle position switch for not less than 1
second but not more than 3 seconds. (Press the
accelerator pedal.)
2. Turn on the idle position switch for not less than 1
second but not more than 3 seconds. (Release the
accelerator pedal.)
3. Turn off the idle position switch for not less than 1
second but not more than 3 seconds. (Press the
accelerator pedal.)
4. Turn on the idle position switch for not less than 1
second but not more than 3 seconds. (Release the
accelerator pedal.)
5. Turn off the idle position switch for not less than 1
second but not more than 3 seconds. (Press the
accelerator pedal.)
6. After the above operations are properly completed,
the CHECK ENGINE lamp (MIL) illuminates for 3
seconds to report the memory is cleared.
Engine Control System 1A-107
LNW21AMF007101-X