Circuit Description
The Engine Coolant Temperature (ECT) sensor is a thermistor immersed in the intake manifold cooling system passage. The VCM applies a voltage on the 5 volt reference circuit to the sensor. When the engine is cold, the sensor (thermistor) resistance is high; therefore, the VCM senses a high signal voltage, and the VCM indicates the coolant temperature. As the engine warms, the sensor resistance becomes less and the voltage drops indicating the high coolant temperature. At the normal engine operating temperature (85°C to 95°C), the voltage measures about 1.5 to 2.0 volts. This DTC is a type D DTC.
Conditions for Setting The DTC
The DTC sets when the signal voltage indicates an engine coolant temperature voltage above 4.9 and the engine run time is greater than 5 seconds.
Action Taken When the DTC Sets
The VCM stores the DTC in History if the VCM detects an intermittent problem.
Conditions for Clearing the MIL/DTC
The VCM turns OFF the MIL after 3 consecutive driving trips without a fault condition present. A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles (the coolant temperature has risen 22°C (40°F) from the start-up coolant temperature and the engine coolant temperature exceeds 71°C (160°F) during that same ignition cycle) or the scan tool clearing feature has been used.
Diagnostic Aids
Check the harness routing for a potential short to ground in the 5 volt reference circuit.
The scan tool displays the engine temperature in degrees centigrade. After the engine is started, the temperature should rise steadily to about 90°C then stabilize when the thermostat opens.
Use the Temperature vs. Resistance Value scale to test the coolant sensor at various temperature levels in order to evaluate the possibility of a skewed or mis-scaled sensor. A skewed sensor could result in poor driveability complaints. Refer to Temperature vs Resistance .
Test Description
The numbers below refer to the step numbers in the diagnostic table.
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If the fault is present, the engine coolant temperature voltage measures greater than 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 low voltage, the VCM and the wiring are OK.
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This test checks for an open or grounded signal sensor circuit. Also being checked are the ECT sensor ground circuit and the VCM.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 |
Important: Before clearing DTCs, use the scan tool in order to record the freeze frame and the failure records for reference because the Clear Info function will lose the data. Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | ||
Does the scan tool display the ECT sensor voltage greater than the specified value? | 4.9 V | |||
Does the scan tool display the ECT sensor voltage less than the specified value? | 0.82 V | |||
Jumper the ECT sensor signal to a known good ground. Does the scan tool display the ECT sensor voltage less than the specified value? | 0.82 V | |||
5 | The DTC is intermittent. If no additional DTCs are stored, refer to the Diagnostic Aids. If additional DTCs are stored, refer to those tables. Are any additional DTCs stored? | -- | Go to The Applicable DTC Table | |
6 | Inspect the ECT sensor ground connector and the VCM connector for proper connection. Was a problem found? | -- | ||
7 | Check the ECT sensor ground circuit for an open between the ECT sensor and the VCM. Was a problem found? | -- | ||
8 | Is the DTC P0123 also set? | -- | Go to DTC P0123 Throttle Position (TP) Sensor Circuit High Voltage | |
9 | Check the ECT sensor signal circuit for an open between the ECT sensor and the VCM. Was a problem found? | -- | ||
10 | Repair the circuit as necessary. Refer to Wiring Repairs in Engine Electrical. Is the action complete? | -- | -- | |
11 | Replace the ECT sensor. Refer to Engine Coolant Temperature (ECT) Sensor Replacement for the 4.3L, 5.0L, 5.7L. Refer to Engine Coolant Temperature Sensor Replacement for the 7.4L Is the action complete? | -- | -- | |
12 | Replace the VCM. Important: If the VCM is faulty, reprogram the VCM. Refer to VCM Replacement/Programming . Is the action complete? | -- | -- | |
13 |
Does the scan tool indicate that this diagnostic ran and passed? | -- | ||
14 | Using the scan tool, select the Capture Info and the Review Info. Are any DTCs displayed that have not been diagnosed? | -- | Go to The Applicable DTC Table | System OK |
