Circuit Description
The engine coolant temperature (ECT) sensor is a thermistor mounted in the engine coolant stream. The engine control module (ECM) applies a voltage of about 5 volts through a pull up resistor to the ECT signal circuit. When the engine coolant is cold, the sensor resistance is high signal voltage. As the engine coolant warms, the sensor resistance is less, and the ECT signal voltage measured at the ECM drop. With the fully warmed up engine, the ECT signal voltage should measure about 1.5-2 volts. If the ECM detects the ECT sensor that is stuck within an expected range of movement.
Conditions for Setting the DTC
| • | DTCs P0106, P0107, P0108, P0112, P0113, P0115, P0117, P0118, P0122, P0123, P0171, P0172, P0201, P0202, P0203, P0204, P0300, P0337, P0351, and P0352 are not set. |
| • | The engine is running. |
| • | Engine soak time is greater than 360 minutes. |
| • | Accumulated decel fuel cutoff (DFCO) is less than 150 seconds. |
| • | Ambient is between -39°C and +35°C. |
Action Taken When the DTC Sets
| • | The malfunction indicator lamp (MIL) will illuminate. |
| • | The ECM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame and Failure Records buffers. |
| • | A history DTC is stored. |
| • | Both cooling fans turn ON. |
| • | The ECM will default to 20°C (68°F) for the first 60 seconds of engine run time and then to 92°C (198°F). The scan tool may show the defaulted value. |
Conditions for Clearing the MIL/DTC
| • | The MIL will turn OFF after 4 consecutive ignition cycles in which the diagnostic runs without a fault. |
| • | A history DTC will clear after 40 consecutive warm-up cycles without a fault. |
| • | The DTCs can be cleared by using the scan tool. |
Diagnostic Aids
| • | Normal operating temperature for the engine cooling system is between 90-95°C (194-203°F). |
| • | Use the Temperature vs. Resistance Values Table to evaluate the possibility of a skewed sensor. Refer to Temperature Versus Resistance . |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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The Diagnostic System Check prompts the technician to complete some basic checks and store the Freeze Frame and Failure Records data on the scan tool, if applicable. This creates an electronic copy of the data taken when the malfunction occurred. The information is then stored on the scan tool for later reference.
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The engine must be allowed to cool fully before the ECT and IAT sensor will read close to the ambient temperature in order to check for a possible skewed sensor.
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Measure the engine coolant temperature with a thermometer to determine the actual value the ECT sensor should be. Take into consideration if the engine has been run and the engine coolant has been warmed without opening the thermostat.
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The replacement ECM must be reprogrammed. Refer to the latest Techline procedure for ECM reprogramming.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Did you Perform the Diagnostic System Check - Engine Controls? | -- | Go to Step 2 | ||
2 |
Does the scan tool display DTC P0117 or P0118? | -- | Go to Step 3 | |
Are the temperature readings close? | -- | Go to Step 5 | Go to Step 4 | |
Does the ECT sensor accurately reflect the actual engine coolant temperature? | -- | Go to Step 5 | Go to Step 9 | |
5 | Disconnect the ECT sensor electrical connector. Is the ECT sensor value less than the specified value? | -30°C (-22°F) | Go to Step 6 | Go to Step 8 |
6 | Jumper the ECT sensor signal circuit, terminal 1 and sensor ground circuit, terminal 2 together at the ECT sensor connector. Is the ECT sensor value greater than the specified value? | 130°C (266°F) | Go to Diagnostic Aids | Go to Step 7 |
7 | Inspect the ECT sensor electrical connector terminals 2 and 1 and the engine control module (ECM) electrical terminals M28 and M64 for poor connectors or malfunctioning terminals and repair as necessary. Did you complete the repair? | -- | Go to Step 10 | Go to Step 8 |
Is the action complete? | -- | Go to Step 10 | System OK | |
9 |
Is the action complete? | -- | Go to Step 10 | System OK |
10 |
Does the scan tool indicate that this diagnostic ran and passed? | -- | Go to Step 11 | Go to Step 2 |
11 | Check if any additional DTCs are set. Are any DTCs displayed that have not been diagnosed? | -- | System OK |
