Circuit Description
The engine coolant temperature (ECT) sensor is a thermistor that controls signal voltage to the PCM. When the engine is cold, the sensor resistance is high, therefore the PCM will see high signal voltage. As the engine warms, sensor resistance becomes less and voltage drops. The voltage measured across the thermistor is interpreted as a temperature.
Conditions for Running the DTC
| • | The PCM performs this DTC diagnostic continuously. |
| • | The engine operation time is more than 8 minutes. |
Conditions for Setting the DTC
| • | The engine coolant temperature is less than or equal to -40°C (-40°F). |
| • | All of the diagnostic set conditions met for 2 seconds. |
Action Taken When the DTC Sets
| • | The PCM illuminates the malfunction indicator lamp (MIL) on the second consecutive drive trip that the diagnostic runs and fails. |
| • | The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the Failure Records will store this information. If the diagnostic reports a failure on the second consecutive drive trip, the Freeze Frame records the operating conditions at the time of failure and updates the Failure Records. |
Conditions for Clearing the MIL/DTC
| • | The PCM will turn the MIL off after 3 consecutive trips without a fault condition. |
| • | A history DTC clears after 40 consecutive warm-up cycles, if this or any other emission related diagnostic does not report any failures. |
| • | The scan tool Clear Info function was used. |
Diagnostic Aids
Check harness routing for a potential short to voltage. After engine is started, the ECT temperature should rise steady to about 85°C (185°F). A skewed sensor could result in poor driveability complaints. Refer to Temperature Versus Resistance .
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 check any circuitry that is suspected of causing the intermittent complaint. Refer to Testing for Electrical Intermittents in Wiring Systems.
If a repair is necessary, then refer to Wiring Repairs or Connector Repairs in Wiring Systems.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step determines if P0118 is a hard failure or an intermittent condition.
-
This step will determine if there is a wiring problem or a malfunctioning PCM.
-
This step determines if there is a short to voltage on the signal circuit. A short to voltage increases current flow through the sensor which overwhelms the sensor. This doesn't allow the sensor to pull down the circuit to the correct voltage and thus display the correct temperature.
-
After repairing the short to voltage, check the sensor for proper operation.
Step
| Action | Values | 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 modules data is deleted once the Clear Info function is used. Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||
Does the ECT display a temperature colder than or equal to the specified value? | -30°C (-22°F) | |||
Does the scan tool display an ECT temperature more than or equal to the specified value? | 151°C (303°F) | |||
4 | Jumper the ECT sensor signal circuit to a known good ground. Does the scan tool display an ECT temperature more than or equal to the specified value? | 151°C (303°F) | ||
5 | The DTC is intermittent. If no other DTCs are stored, refer to Diagnostic Aids. Are there any other DTCs stored? | -- | Go to applicable DTC | Go to Diagnostic Aids |
6 |
Did you perform a repair? | -- | ||
7 |
Did you perform a repair? | -- | ||
8 |
Did you perform a repair? | -- | ||
With a DMM set to the mA scale, measure the current at the ECT harness connector terminals. Is the current less than the specified value? | 48 mA | |||
Repair the short to voltage on the ECT signal circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | ||
11 | Inspect the PCM connectors for proper connections and replace the terminals, if necessary. Refer to Wiring Repairs in Wiring Systems. Did you perform a repair? | -- | ||
12 | Replace the ECT sensor. Refer to Engine Coolant Temperature Sensor Replacement . Is the action complete? | -- | -- | |
13 |
Important: The new PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Is the action complete? | -- | -- | |
14 |
Does the scan tool indicate the diagnostic Passed? | -- | ||
15 | Does the scan tool display any additional undiagnosed DTCs? | -- | Go to applicable DTC | System OK |
