P0118
DTC P0118
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 high ECT signal voltage, which is a low temperature indication, this DTC sets.
The table illustrates the difference between temperature, resistance, and voltage.
DTC DESCRIPTOR
This diagnostic procedure supports the following DTC:
DTC P0118 Engine Coolant Temperature (ECT) Sensor Circuit High Voltage
CONDITIONS FOR RUNNING THE DTC
- The ignition is ON or the engine is operating.
- DTC P0118 runs continuously once the above condition is met.
CONDITIONS FOR SETTING THE DTC
The ECM detects that the ECT is less than -42°C (-43.6°F) for more than 4 seconds. The scan tool is limited to -40°C (-40°F), so the diagnostic procedure uses -39°C (-38°F) to determine if there is an ECT condition.
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
- Use the J 35616 Connector Test Adapter Kit for any test that requires probing the ECM harness connector or a component harness connector.
- The lower connector of the ECM is connector C1 and the upper connector of the ECM is connector C2. Refer to Engine Controls Component Views.
- 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°F), refer to Temperature Versus Resistance - Engine Coolant Temperature Sensor.
- After starting the engine, the ECT should rise steadily to about 90°C (194°F) then stabilize when the thermostat opens.
- For an intermittent condition, refer to Intermittent Conditions. Intermittent Conditions
TEST DESCRIPTION
Step 1 - Step 8:
Step 9 - Step 19:
The numbers below refer to the step numbers in the diagnostic table.
6. This step is testing the low reference circuit for a short to voltage or for a low reference circuit that is open. If the low reference circuit within the ECM is open or if the low reference circuit is open between the ECM and the splice, a voltage of 3-5 volts will be measured on the DMM.
7. This step isolates if there is a circuit that is shorted to voltage or if the low reference circuit is open internally or externally of the ECM. If there is no voltage on the low reference circuit after disconnecting all the sensors, the low reference circuit is open.