Circuit Description
The engine coolant temperature (ECT) sensor is a thermistor. The control module supplies the ECT sensor with a reference voltage on the ECT signal circuit and a ground circuit. When the ECT sensor resistance is high, indicating a cold sensor, the ECT sensor signal voltage remains near the supplied voltage. The ECT sensor decreases the signal voltage as the ECT sensor resistance is low, indicating a warm sensor. The control module monitors the ECT sensor signal circuit voltage in order to calculate the engine temperature.
This DTC is designed to detect intermittent low voltage signals on the ECT sensor signal circuit.
Conditions for Running the DTC
The engine has been running for more than 5 seconds
Conditions for Setting the DTC
The ECT voltage is less than 0.25 volts for more than 1 second
Action Taken When the DTC Sets
The VCM stores the DTC in History if the VCM detects an intermittent problem.
Conditions for Clearing the MIL or DTC
| • | The control module turns OFF the MIL after 3 consecutive drive trips when the test has run and passed. |
| • | A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles. A warm-up cycle occurs when the coolant temperature has risen 22°C (40°F) from the startup coolant temperature and the engine coolant reaches a temperature that is more than 70°C (158°F) during the same ignition cycle. |
| • | Use a scan tool in order to clear the DTCs. |
Diagnostic Aids
A poor connection or an open in the 5 volt reference circuit or the ECT sensor ground circuit results in a DTC P1115.
The scan tool displays the engine temperature in degrees centigrade. After the engine is started, the temperature should rise steadily to about 90°C then stabilize when the thermostat opens.
Use the Temperature vs. Resistance Value scale in order to test the coolant sensor at various temperature levels in order to evaluate the possibility of a skewed or mis-scaled sensor. A skewed sensor could result in poor driveability complaints. Refer to Temperature vs Resistance .
An intermittent may be caused by a poor connection, rubbed through wire insulation, or a broken wire inside the insulation.
Thoroughly check any circuitry that is suspected of causing the intermittent complaint for the following conditions:
| • | Backed out terminals |
| • | Improper mating |
| • | Broken locks |
| • | Improperly formed or damaged terminals |
| • | Poor terminal to wire connections |
| • | Physical damage to the wiring harness |
| • | Corrosion |
| • | Moisture in the connector |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
If the ECT sensor voltage is less than 0.24 volts, then the conditions for the DTC are still present.
-
If any other non-intermittent DTCs are set go there first.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 |
Important: Before clearing the DTCs, use the scan tool Capture Info to save the Freeze Frame and Failure records for reference. The control module's data is deleted once the Clear Info function is used. Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||
Is the ECT sensor voltage less than the specified value? | 0.24V | |||
Are any non-intermittent DTCs set? | -- | Go to the applicable DTC table | ||
4 |
Did you find a problem? | -- | ||
5 |
Did you find a problem? | -- | ||
6 |
Did the voltage fluctuate? | -- | Go to Diagnostic Aids | |
7 | Repair the circuit as necessary. Refer to Wiring Repairs . Is the action complete? | -- | -- | |
8 |
Does the scan tool indicate the diagnostic Passed? | -- | ||
9 | Does the scan tool display any additional undiagnosed DTCs? | -- | Go to the applicable DTC table | System OK |
