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 diagnostic is designed to detect intermittent low voltage signals on the ECT sensor signal circuit.
Conditions for Running the DTC
The engine run time is more than 5 seconds.
Conditions for Setting the DTC
The vehicle control module (VCM) detects an intermittent low ECT voltage while the engine is running and run time exceeds 5 seconds.
Action Taken When the DTC Sets
| • | The control module stores the DTC in history after the first failure but will not illuminate the malfunction indicator lamp (MIL). |
| • | The control module records the operating conditions at the time the diagnostic fails. The control module stores the failure information in the scan tools Freeze Frame/Failure Records. |
Conditions for Clearing the MIL/DTC
| • | 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 temperature exceeds 70°C (160°F) during the same ignition cycle. |
| • | Use the scan tool Clear Information function. |
Diagnostic Aids
An intermittent short to ground in the ECT sensor signal circuit could result in DTC P1114.
The scan tool displays the engine temperature in degrees centigrade. After the engine is started, the temperature should rise steadily to about 90°C (194°F) 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.
Inspect for intermittents.
An intermittent may be caused by any of the following conditions:
| • | A poor connection |
| • | Rubbed through wire insulation |
| • | A broken wire inside the insulation |
Thoroughly inspect any circuitry that is suspected of causing the intermittent complaint. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
If a repair is necessary, refer to Wiring Repairs or Connector Repairs in Wiring Systems.
Test Description
The number below refers to the step number on the diagnostic table.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | Go to Step 2 | |
Is the voltage less than the specified value? | 0.25 V | Go to DTC P0117 Engine Coolant Temperature (ECT) Sensor Circuit Low Voltage | Go to Step 3 | |
3 |
Did you find a problem? | -- | Go to Step 6 | Go to Step 4 |
4 |
Did you find a problem? | -- | Go to Step 6 | Go to Step 5 |
5 |
Does the voltage fluctuate? | -- | Go to Step 6 | Go to Diagnostic Aids |
6 | Repair the circuit as necessary. Refer to Wiring Repairs or to Connector Repairs in Wiring Systems. Is the action complete? | -- | Go to Step 7 | -- |
7 |
Does the scan tool indicate the diagnostic Passed? | -- | Go to Step 8 | Go to Step 2 |
8 | Does the scan tool display any additional undiagnosed DTCs? | -- | Go to the applicable DTC table | System OK |
