Circuit Description
The engine coolant temperature sensor is a thermistor immersed in the intake manifold cooling system passage which is used to monitor the temperature of the engine coolant. The VCM applies 5 volts to the sensor on the 5 volt reference circuit. When the coolant is cool, the resistance in the sensor reads high and the VCM senses a high voltage signal. When the coolant is warm, the sensor resistance reads low and the VCM senses a low voltage signal. This is a type A DTC.
Conditions for Setting the DTC
The following conditions will set the DTC:
| • | The engine is running |
| • | The signal voltage indicates an engine coolant temperature voltage above 4.9 volts for 5 seconds. |
Action Taken When the DTC Sets
The VCM turns ON the MIL when this DTC is reported and 1 failure has occurred.
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. After starting the engine, the temperature should rise steadily to about 90°C (194°F), then stabilize when the thermostat opens.
Use the Temperature vs Resistance Value table in order 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 result in poor driveability complaints. Refer to Temperature vs Resistance .
Test Description
The numbers below refer to the step numbers on 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 message, the VCM and the wiring are okay.
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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 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 circuit 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 were stored, refer to the Diagnostic Aids. If the additional DTCs are stored, refer to those tables. | -- | Go to The Applicable DTC Table | |
6 | Inspect the ECT sensor connector and the VCM connector for the 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 repair complete? | -- | -- | |
11 | Replace the ECT sensor. Refer to Engine Coolant Temperature (ECT) Sensor Replacement for the 4.3L. Is the replacement complete? | -- | -- | |
12 | Replace the VCM. Important: If the VCM is faulty, reprogram the VCM. Refer to VCM Replacement/Programming . Is the replacement complete? | -- | -- | |
13 |
for setting this DTC as specified in the supporting text. 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 |
