Isuzu 4ja1, Workshop Manual

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Engine Control System (4JH1) 6E-77
DTC P0115 (Symptom Code 1) (Flash Code 14)
Circuit Description
The engine coolant temperature (ECT) sensor is
installed to the thermostat housing. The ECT sensor is
a variable resistor. The ECT sensor has a signal circuit
and a low reference circuit. The ECT sensor measures
the temperature of the engine coolant. The engine
control module (ECM) supplies 5 volts to the ECT signal
circuit and a ground for the ECT low reference circuit.
When the ECT sensor is cold, the sensor resistance is
high. When the engine coolant temperature increases,
the sensor resistance decreases. With high sensor
resistance, the ECM detects a high voltage on the ECT
signal circuit. With lower sensor resistance, the ECM
detects a lower voltage on the ECT signal circuit. If the
ECM detects an excessively high ECT signal voltage,
this DTC will set.
Condition for Running the DTC
•
The ignition switch is ON.
Condition for Setting the DTC
•
The ECM detects that the ECT sensor signal
voltage is more than 4.7 volts for 3 seconds.
Action Taken When the DTC Sets
•
The ECM illuminates the malfunction indicator
lamp (MIL) when the diagnostic runs and fails.
•
The ECM uses an ECT substitution of fuel
temperature for engine control.
•
The ECM uses an ECT substitution of 60
°
C
(120
°
F) for injection timing control.
•
The ECM uses an ECT substitution of -15
°
C (5
°
F)
for glow control.
Condition for Clearing the MIL/DTC
•
The ECM turns OFF the MIL when the diagnostic
runs and does not fail.
•
A history DTC clears after 40 consecutive driving
cycles without a fault. Or clear with the scan tool.
Diagnostic Aids
•
If an intermittent condition is suspected, refer to
Intermittent Conditions in this section.
•
After starting the engine, the ECT should rise
steadily to about 80°C – 85°C (176°F – 185°F)
then stabilize when the thermostat opens.
•
Use the Temperature vs. Resistance table to test
the ECT sensor at various temperature levels to
evaluate the possibility of a skewed sensor. A
skewed sensor could result in poor driveability
concerns.
DTC P0115 (Symptom Code 1) (Flash Code 14)
Schematic Reference:
Engine Controls Schematics
Connector End View Reference: Engine Controls
Connector End Views or Engine Control Module (ECM)
Connector End Views
Step Action
Value(s)
Yes No
1 Did you perform the Diagnostic System Check-
Engine Controls?

Go to Step 2
Go to Diagnostic
System Check-
Engine Controls
2 1. Install the scan tool.
2. Turn ON the ignition, with the engine OFF.
3. Observe the Engine Coolant Temperature (ECT)
parameter with the scan tool.
Is the ECT parameter less than the specified value?
-35°C (-31°F)
Go to Step 3
Go to Diagnostic
Aids
3 1. Turn OFF the ignition.
2. Disconnect the ECT sensor harness connector.
3. Connect a DMM between the signal circuit of the
ECT sensor harness (pin 1 of E-41 connector)
and a known good ground.
4. Turn ON the ignition, with the engine OFF.
Is the DMM voltage more than the specified value?
5.5 volts
Go to Step 4 Go to Step 5
4 Important: The ECT sensor may be damaged if the
sensor signal circuit is shorted to a voltage source.
1. Test the signal circuit between the engine control
module (ECM) (pin 8 of C-57 connector) and the
ECT sensor (pin 1 of E-41 connector) for a short
to battery or ignition voltage.
2. Repair the circuit(s) as necessary.
Did you find and correct the condition?

Go to Step 14 Go to Step 13