Circuit Description
The Engine Coolant Temperature (ECT) sensor is a thermistor that controls the signal voltage to the ECM. The ECM applies a voltage on ECT signal circuit to the sensor. When the engine is cold, the sensor (thermistor) resistance is high; therefore, the ECM will see a high signal voltage.
As the engine warms, the sensor resistance becomes less and the voltage drops. At the normal engine operating temperature 85°C to 95°C, (185°F to 200°F) the voltage will measure about 1.5 to 2.0 volts.
Conditions for Setting the DTC
The signal voltage indicates an engine coolant temperature less than -44°C (-47°F) for 3 seconds.
Action Taken When the DTC Sets
The Malfunction Indicator Lamp (MIL) will illuminate. The system will go Open Loop.
Conditions for Clearing the MIL/DTC
The conditions for the fault are no longer present and 50 ignition cycles have passed with no further faults or the ignition switch is turned OFF and the battery feed voltage is removed for 10 seconds.
Diagnostic Aids
A scan tool reads the engine temperature in degrees centigrade. After the engine starts, the temperature should rise steadily to about 90°C (195°F) then stabilize when thermostat opens.
A faulty connection or an open in ECT signal or sensor ground circuit will result in a DTC 15.
Refer to Intermittent Conditions .
Use the Temperature vs Resistance table in order to test the ECT sensor at various temperature levels in order to evaluate the possibility of a skewed (mis-scaled) sensor. A skewed sensor could result in poor driveability complaints.
Test Description
The numbers below refer to the step numbers on the Diagnostic Table.
-
This step checks to see if DTC set as a result of a hard failure or an intermittent condition.
-
This test simulates a DTC 14. If the ECM recognizes the low signal voltage, high temperature, and the scan reads 130°C (266°F) or above, the ECM and wiring are OK.
-
This test determines if the ECT signal circuit is open. There should be 5 volts present at the sensor connector if measured with a J 39200 .
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Did you perform the On-Board Diagnostic (OBD) System Check? | -- | ||
Install a scan tool. Does the scan tool display the engine coolant temperature at or less than the specified value? | -30°C (-22°F) | Go to Diagnostic Aids | ||
Does the scan tool display the engine coolant temperature greater than the specified value? | 130°C (266°F) | |||
4 |
Did you find a problem? | -- | ||
5 | Replace the engine coolant temperature (ECT) sensor. Refer to Engine Coolant Temperature Sensor Replacement . Is the action complete? | -- | -- | |
Jumper the (ECT) sensor signal circuit to ground. Does the scan tool display engine coolant temperature greater than the specified value? | 130°C (266°F) | |||
7 |
Did you find a problem? | -- | ||
8 |
Did you find a problem? | -- | ||
9 |
Did you find a problem? | -- | ||
10 | Replace the ECM. Refer to Engine Control Module Replacement . Is the action complete? | -- | -- | |
11 |
Did the DTC reset? | -- | ||
12 | Does the scan tool display any additional, undiagnosed DTCs? | -- | Go to the Applicable DTC Table | System OK |
