Isuzu engine C22NE / 22LE / 20LE. Service manual — part 82
DRIVEABILITY AND EMISSIONS 6E1-157
0.75
G
0.75
L
0.5
R
0.5
GRN
0.5
L/R
Engine
Control
Module
(ECM)
A3
F14
B1
B8
ECT
Sensor
Input
Sensor
Ground
Engine
Coolant
Temperature
(ECT)
Sensor
B
A
TPS
HI
OUT
LO
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).
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.
6E1-158 DRIVEABILITY AND EMISSIONS
Diagnostic Aids
Check for the following conditions:
• Poor connection at ECM - Inspect harness
connectors for backed-out terminals, improper
mating, broken locks, improperly formed or
damaged terminals, and poor terminal-to-wire
connection.
• Damaged harness - Inspect the wiring harness for
damage, If the harness appears to be OK, observe
the ECT display on the Scan Tool while moving
connectors and wiring harnesses related to the ECT
sensor. A change in the ECT display will indicate
the location of the fault.
Test Description
Number(s) below refer to the step number(s) on the
Diagnostic Chart.
2. Verifies that the fault is present.
3. Refer to the "Temperature vs. Resistance Value"
table. The table may be used to test the ECT
sensor at various temperatures to evaluate the
possibility of a "shifted" sensor that may be stored
above or below a certain temperature. If this is the
case, replace the ECT sensor. If the ECT sensor
appears to be OK, the fault is intermittent; refer to
Diagnostic Aids.
Engine Coolant Temperature Sensor
°C
°F
OHMS
Temperature vs. Resistance Values
(approximate)
100
212
177
80
176
332
60
140
667
45
113
1188
35
95
1802
25
77
2796
15
59
4450
5
41
7280
−5
23
12300
−15
5
21450
−30
−22
52700
−40
−40
100700
DTC (Flash DTC = 15)
Engine Coolant Temperature (ECT) Sensor Circuit Low Input
Step
Action
Value(s)
Yes
No
1
Was the "On-Board Diagnostic (OBD) System Check"
performed?
-
Go to Step 2
Go to OBD
System
Check
2
1. Ignition ON, engine OFF
2. Observe the "Eng Coolant Temp" displayed on the
Scan Tool.
Is the "Eng Coolant Temp" below the specified value?
140°C
(284°F)
Go to Step 4
Go to Step 3
3
1. Ignition ON, engine OFF.
2. Using a Scan Tool, monitor info for Diagnostic Trouble
Code 15.
Does the Scan Tool indicate Diagnostic Trouble Code 15?
-
Go to Step 4
Refer to
Diagnostic
Aids
4
1. Disconnect the ECT sensor electrical connector.
2. Observe the "Eng Coolant Temp" displayed on the
Scan Tool.
Is the "Eng Coolant Temp" at the specified value?
−35°C
(
−31°F)
Go to Step 6
Go to Step 5
DRIVEABILITY AND EMISSIONS 6E1-159
DTC (Flash DTC = 15)
Engine Coolant Temperature (ECT) Sensor Circuit Low Input (Cont'd)
Step
Action
Value(s)
Yes
No
5
1. Ignition OFF.
2. Disconnect the ECM and check the ECT circuit for a an
open or a short to battery in the sensor circuit.
3. If the ECT circuit is short to battery or open, repair it as
necessary.
Was the ECT signal circuit shorted to ground?
-
Verify repair
Go to Step 7
6
Replace the ECT sensor.
Is the action complete?
-
Verify repair
-
7
Replace the EPROM or ECM.
Is the action complete?
Note) Refer to 6E1-243.
-
Verify repair
-
6E1-160 DRIVEABILITY AND EMISSIONS
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