Circuit Description
The engine coolant temperature (ECT) sensor uses a thermistor in order to control the signal voltage to the Powertrain Control Module (PCM). The PCM supplies a voltage on the signal circuit to the sensor. When the engine is cold, the sensor resistance is high and the ECT signal voltage will be high.
As the engine warms, the sensor resistance becomes less and the voltage drops. At the normal engine operating temperature, the voltage will be between 1.5 and 2.0 volts at the ECT signal terminal.
The ECT sensor controls the following items:
| • | The fuel delivery |
| • | The torque converter clutch (TCC) |
| • | The ignition control (IC) |
| • | The evaporative emission (EVAP) canister purge valve |
| • | The idle air control (IAC) valve |
| • | The electric cooling fan |
Conditions For Running The DTC
The engine run time is more than 60 seconds.
Conditions for Setting the DTC
The ECT sensor indicates that the engine coolant temperature is less than -40°C (-40°F) for 6.25 seconds.
Action Taken When the DTC Sets
| • | The malfunction indicator lamp (MIL) will illuminate after two consecutive ignition cycles in which the diagnostic runs with the fault active. |
| • | The PCM will record the operating conditions at the time that the diagnostic fails. This information will store in the Freeze Frame and Failure Records buffers. |
| • | A history DTC stores. |
| • | The coolant fan turns ON. |
| • | The PCM will default to 20°C (68°F) for the first 60 seconds of the engine run time and then to 92°C (198°F). |
Conditions for Clearing the MIL/DTC
| • | The MIL will turn OFF after three 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. |
| • | Use a scan tool to clear the DTCs. |
Diagnostic Aids
| • | The normal operating temperature for the engine cooling system is between 90°C (194°F) and 95°C (203°F). |
| • | Use the Temperature vs. Resistance table in order 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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If the condition is present, the ECT sensor temperature measures less than -30°C (-22°F).
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This test simulates the conditions for a DTC P0117. If the PCM recognizes the grounded circuit, or low voltage, and displays a low temperature, the PCM and the wiring are okay.
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This test checks for an open or grounded ECT sensor signal circuit. The ECT sensor ground circuit and the PCM are also being checked.
-
This test checks for a short to voltage on the ECT sensor signal circuit.
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After repairing a short to voltage, it is necessary to recheck the operation of the ECT sensor.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||
Does the scan tool display an ECT sensor temperature less than the specified value? | -30°C (-22°F) | |||
Does the scan tool display an ECT sensor temperature more than the specified value? | 130°C (266°F) | |||
Jumper the ECT sensor signal circuit to a ground. Does the scan tool display an ECT sensor temperature more than the specified value? | 130°C (266°F) | |||
Is the voltage more than the specified value? | 5.20 V | |||
6 | The DTC is intermittent. Are any additional DTCs stored? | -- | Go to Diagnostic Aids | |
7 | Check the ECT sensor harness connector and the PCM connector for a faulty connection. Did you find a problem? | -- | ||
8 | Check the ECT sensor ground circuit for an open or faulty connection between the ECT sensor and the PCM. Did you find a problem? | -- | ||
9 | Check the ECT sensor signal circuit for an open or faulty connection between the ECT sensor and the PCM. Did you find a problem? | -- | ||
10 | Repair the short to voltage in the ECT sensor signal circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |
11 | Repair the circuit as necessary. Refer to Wiring Repairs or Connector Repairs in Wiring Systems. Is the action complete? | -- | -- | |
Does the scan tool display an ECT sensor temperature more than the specified value? | -30°C (-22°F) | |||
13 | Replace the ECT sensor. Refer to Engine Coolant Temperature Sensor Replacement . Is the action complete? | -- | -- | |
14 |
Important: Refer to Powertrain Control Module Replacement/Programming . Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | -- | |
15 |
Does the scan tool indicate the diagnostic Passed? | -- | ||
16 | Does the scan tool display any additional undiagnosed DTCs? | -- | System OK |
