Circuit Description
The engine coolant temperature (ECT) sensor is a variable resistor that measures the temperature of the engine coolant. The engine control module (ECM) supplies 5 volts to the ECT signal circuit and supplies a ground to the low reference circuit. If the ECM detects a low ECT signal voltage, which is a high temperature indication, this DTC sets.
The following table illustrates the difference between temperature, resistance, and voltage:
ECT | ECT Resistance | ECT Signal Voltage |
|---|---|---|
Cold | High | High |
Warm | Low | Low |
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0117 Engine Coolant Temperature (ECT) Sensor Circuit Low Voltage
Conditions for Running the DTC
| • | The engine is operating. |
| • | The start up intake air temperature (IAT) is less than 72°C (161°F). |
| OR |
| • | The engine is operating. |
| • | The start up IAT is more than 72°C (161°F). |
| • | The engine run time is more than 59 seconds. |
| • | DTC P0117 runs continuously once the above condition is met. |
Conditions for Setting the DTC
The ECM detects that the engine coolant temperature is more than 140°C (284°F) for more than 4 seconds.
Action Taken When the DTC Sets
| • | The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails. |
| • | The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records. |
Conditions for Clearing the MIL/DTC
| • | The control module turns OFF the malfunction indicator lamp (MIL) after 4 consecutive ignition cycles that the diagnostic runs and does not fail. |
| • | A current DTC, Last Test Failed, clears when the diagnostic runs and passes. |
| • | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic. |
| • | Clear the MIL and the DTC with a scan tool. |
Diagnostic Aids
The following table illustrates the ECM connector locations:
ECM Connector Location | |
|---|---|
C2 | C1 |
Front of Vehicle | |
| • | Use the J 35616-A/BT-8637 GM Approved Terminal Test Kit for any test that requires probing the ECM harness connector or a component harness connector. |
| • | An overheating condition may cause this DTC to set. |
| • | After starting the engine, the ECT should rise steadily to about 90°C (194°F) then stabilize when the thermostat opens. |
| • | 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 sensor. A skewed sensor could result in a driveability condition. If the engine has sat overnight, the engine coolant temperature and the intake air temperature values should display within a few degrees. If the temperatures are not within 3°C (5.4°F), refer to Temperature Versus Resistance - Engine Coolant Temperature Sensor . |
| • | For an intermittent condition, refer to Intermittent Conditions . |
Test Description
The numbers below refer to the step numbers in the diagnostic table.
-
This step determines that a condition exists. If the temperature is more than the specified value, test for a condition in the circuits of the ECT sensor.
-
This step isolates the condition. If the temperature is less than the specified value, the ECM and the signal circuit of the ECT sensor are OK.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Engine Control Module Connector End Views or Engine Controls Connector End Views | ||||
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | |
Is the temperature more than the specified value? | 140°C (284°F) | Go to Step 4 | Go to Step 3 | |
3 |
Did the DTC fail this ignition? | -- | Go to Step 4 | Go to Diagnostic Aids |
Is the temperature less than the specified value? | -39°C (-38°F) | Go to Step 6 | Go to Step 5 | |
5 |
Did you find and correct the condition? | -- | Go to Step 8 | Go to Step 7 |
6 | Replace the ECT sensor. Refer to Engine Coolant Temperature Sensor Replacement . Did you complete the replacement? | -- | Go to Step 8 | -- |
7 | Replace the ECM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 8 | -- |
8 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 9 |
9 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK | |
