Circuit Description
The engine coolant temperature (ECT) sensor is a thermistor which controls the signal voltage to the powertrain control module (PCM). The PCM supplies a 5 volt reference and a ground to the ECT sensor. Whenever the engine is cold, the ECT sensor resistance will be high.
As the engine warms up, the ECT sensor resistance decreases and the voltage drops. At the normal engine operating temperature, the voltage will be between 1.5 and 2.0 volts.
The engine coolant temperature sensor is one of the inputs used to control 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 |
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) illuminates after 2 consecutive ignition cycles with the malfunction present. |
| • | The PCM records the operating conditions at the time the diagnostic fails. The Freeze Frame and Failure Records buffers stores this information. |
| • | A history DTC is stored. |
| • | The PCM defaults to 20°C (68°F) for the first 60 seconds of engine run time. After 60 seconds the ECT will default to 92°C (198°F) for engine coolant temperature. The scan tool will not show the defaulted value. |
Conditions for Clearing the MIL/DTC
| • | The MIL will turn OFF after 3 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. |
| • | A scan tool can clear the DTCs. |
Diagnostic Aids
After starting the engine, the temperature should rise steadily to about 90°C (194°F) then stabilize when the thermostat opens.
Check for an intermittent short to ground in the ECT sensor signal circuit by moving the PCM harness at various locations while monitoring the ECT voltage on the scan tool. If the voltage varies, look for a short to ground in the area of the harness that caused the variance. For more information about intermittence Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
Use the Temperature vs. Resistance value table to test the coolant sensor at various temperature levels in order to evaluate the possibility of a skewed (mis-scaled) sensor. A skewed sensor could affect vehicle driveability. 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 value will be less than -30° C ( 4.9 volts).
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This test simulates the conditions for a DTC P0117. If the VCM recognizes the grounded circuit (low voltage) and displays a high temperature message, the PCM and the wiring are okay.
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This test checks for an open or grounded ECT sensor signal circuit. Also being checked are the ECT sensor ground circuit and the PCM.
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This test checks for a short to voltage on the ECT sensor signal circuit.
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After repairing a short to voltage, recheck the operation of the ECT sensor.
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Reprogram the replacement PCM and perform the Crankshaft Position System Variation Learn Procedure. Refer to the latest Techline information for PCM programming .
Step | Action | Values | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check ? | -- | ||
Does the scan tool display an ECT sensor value less than the specified value? | -30° C (-22° F) | |||
Does the scan tool display an ECT sensor value 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 value 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 applicable DTC table | Go to Diagnostic Aids |
7 | Inspect the ECT sensor harness connector and the PCM connector for a poor connection. Did you find a condition? | -- | ||
8 | Inspect the ECT sensor ground circuit for an open or poor connection between the ECT sensor and the PCM. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. Did you find a condition? | -- | ||
9 | Inspect the ECT sensor signal circuit for an open or poor connection between the ECT sensor and the PCM. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. Did you find a condition? | -- | ||
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 value less than the specified value? | -30° C (-22° F) | |||
13 | Replace the ECT sensor. Refer to Engine Coolant Temperature Sensor Replacement . Is the action complete? | -- | -- | |
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Important: The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Is the action complete? | -- | -- | ||
15 |
Does the scan tool indicate the diagnostic Passed? | -- | ||
16 | Does the scan tool display any additional undiagnosed DTCs? | -- | Go to applicable DTC table | System OK |
