Isuzu C22NE Workshop Manual page 327

DIAGNOSTIC TROUBLE CODE (DTC) (Flash DTC = 15)
ENGINE COOLANT TEMPERATURE (ECT) SENSOR CIRCUIT LOW INPUT
Circuit Description
The ECT sensor is a thermistor mounted in the engine
coolant stream. The engine control module (ECM)
applies a voltage (about 5 volts) through a pull-up
resistor to the ECT signal circuit. When the engine
coolant is cold, the sensor (thermistor) resistance is
high, therefore the ECM will measure a high signal
voltage. As the engine coolant warms, the sensor
resistance becomes lower, and the ECT signal voltage
measured at the ECM drops. With a fully warmed-up
engine, the ECT signal voltage should measure about
1.5 to 2.0 volts.
Conditions for Setting the DTC
• Engine running time is longer than 30 secs.
• The ECT sensor signal indicates an engine coolant
temperature less than -35°C (-31°F).
TPS
LO
HI OUT
0.5
R
A3
Engine
Control
Module
(ECM)
DRIVEABILITY AND EMISSIONS 6E1-157
Engine
Coolant
Temperature
(ECT)
Sensor
B A
0.5 0.5
GRN L/R
0.75 0.75
L G
B8 B1 F14
Sensor ECT
Ground Sensor
Input
Action Taken When the DTC Sets
• The ECM will illuminate the malfunction indicator
lamp (MIL) the first time the fault is detected.
• The ECM will substitute the ECT reading with a
default engine coolant temperature value. The
default value is based on start-up intake air
temperature and running time.
Conditions for Clearing the MIL/DTC
Once the ECM determines that a fault(s) has been
rectified then the CEL will switch OFF, although the
fault code will remain in the ECM memory.
Any fault codes will remain in ECM memory until -
1. They are cleared by disconnecting the Battery for
more than 30 seconds.
2. A service tool such as Tech 2 is used to clear them.
3. Ten consecutive starts without logging a fault.