P0118

DTC P0118

CIRCUIT DESCRIPTION




This diagnostic monitors the signal circuit of the engine coolant temperature (ECT) sensor. The ECT sensor is a variable resistor that measures the temperature of the engine coolant. The powertrain control module (PCM) supplies 5 volts to the ECT signal circuit and supplies a ground to the low reference circuit. If the PCM 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.
- DTC P0117, is not set.
- DTC P0118 runs continuously once the above conditions are met.

CONDITIONS FOR SETTING THE DTC
- The PCM detects that the ECT sensor signal voltage is 4.92 volts or more.
- The above condition is present for at least 2 seconds.

ACTION TAKEN WHEN THE DTC SETS
- The powertrain control module (PCM) illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.
- The PCM records the operating conditions at the time the diagnostic fails. The PCM stores this information in the Freeze Frame/Failure Records.
- The PCM enters the Fail Safe Function in which the coolant temperature will use default values and the fuel control system will operate in OPEN LOOP.

CONDITIONS FOR CLEARING THE MIL/DTC
- The PCM turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
- A last test failed, or current DTC, clears when the diagnostic runs and does not fail.
- A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
- Use a scan tool in order to clear the MIL and the DTC.

DIAGNOSTIC AIDS
- If a short to a separate 5-volt source occurs this DTC may set, if this is found to be the condition a continuity test to all other PCM circuits will be necessary to diagnose the specific circuit.
- 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 vs Resistance - Intake Air Temperature (IAT) 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

Steps 1-10:

Steps 11-17:

The numbers below refer to the step numbers on the diagnostic table.
4. This step tests for the proper operation of the circuit in the low voltage range. If the fuse in the jumper opens when you perform this test, the signal circuit is shorted to voltage.
9. This step tests the signal circuit of the ECT sensor for a short to another 5.0 volt reference circuit.
15. After replacing the PCM a new minimum throttle position and idle speed must also be established.