Circuit Description
The Engine Coolant Temperature (ECT) sensor contains a semiconductor device which changes the resistance based on the temperature (a thermistor). The ECT sensor is mounted in bank one cylinder head. The ECT sensor has a signal circuit and a ground circuit. The PCM applies a voltage (about 5.0 volts) on the signal circuit to the sensor. The PCM monitors the changes in this voltage caused by changes in the resistance of the sensor in order to determine the coolant temperature.
When the coolant is cold, the sensor (thermistor) resistance is high, and the PCMs signal voltage is only pulled down a small amount through the sensor to ground. Therefore, the PCM senses a high signal voltage (low temperature). When the coolant is warm, the sensor resistance is low, and the signal voltage is pulled down a greater amount. This causes the PCM to senses a low signal voltage (high temperature). At normal operating temperature, the voltage should measure about 1.5-2.0 volts at the PCM.
When the PCM senses a signal voltage lower than the normal operating range of the ECT sensor, this DTC will set.
Conditions for Running the DTC
Engine operates longer than 20 seconds.
Conditions for Setting the DTC
| • | The PCM indicates Engine Coolant Temperature greater than 139°C (282°F). |
| • | Above condition present for less than a second. |
Action Taken When the DTC Sets
The PCM will illuminate the malfunction indicator lamp (MIL) on the second consecutive drive trip that the diagnostic runs and fails.
The PCM will record operating conditions at the time the diagnostic fails. The first time the diagnostic fails, this information will be stored in Failure Records. If the diagnostic reports a failure on the second consecutive drive trip, the operating conditions at the time of failure will be written to Freeze Frame and the Failure record will be updated.
The PCM will use a default engine coolant temperature.
Conditions for Clearing the MIL/DTC
| Important: If the last failure was during a non-typical driving condition, the MIL may remain ON longer than 3 drive trips. Review Freeze Frame and Failure Records for the last failure conditions. |
| • | The PCM turns the MIL OFF after 3 consecutive drive trips when the test has Run and Passed and not Failed. |
| • | A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles (coolant temperature has risen 22°C (40°F) from the startup coolant temperature and the engine coolant temperature exceeds 70°C (160°F) during the same ignition cycle. |
| • | Use the scan tool Clear Information function. |
| • | A last test failed (Current DTC) will clear when the diagnostic runs and does not fail. |
| • | Disconnect the PCM battery feed for 30 seconds. |
Diagnostic Aids
After starting the engine, the temperature should rise steadily to about 90°C (194°F) then stabilize when the thermostat opens. A poor connection or an open in the 5 volt reference circuit or the sensor ground circuit results in a DTC P0117.
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 result in poor driveability concerns. Refer to Temperature vs Resistance .
For any test that requires probing the PCM or component harness connectors, use the Connector Test Adapter Kit J 35616 . Using this kit prevents any damage to the harness connector terminals.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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This step determines if the malfunction is present.
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Using the Freeze Frame and/or Failure Records data may aid in locating an intermittent condition. If you cannot duplicate the DTC, the information included in the Freeze Frame and/or Failure Records data can help determine how many miles since the DTC set. The Fail Counter and Pass Counter can also help determine how many ignition cycles the diagnostic reported a pass and/or a fail. Operate the vehicle within the same freeze frame conditions (RPM, load, vehicle speed, temperature etc.) that you observed. This will isolate when the DTC failed. For any test that requires probing the PCM or component harness connectors, use the Connector Test Adapter Kit J 35616 . Using this kit prevents any damage to the harness connector terminals.
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An engine coolant temperature below -30°C (-22°F) indicates the PCM and the ECT sensor wiring are OK.
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Disconnecting the PCM allows using the DMM J 39200 in order to check continuity of the circuits. This aids in locating an open or a shorted circuit.
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Inspect for proper terminal tension/connections at the PCM harness before replacing the PCM.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||
|
Important: If the engine is overheating, correct the overheating condition before proceeding with this table.
Is the ECT sensor above the specified value? | 139°C (282°F) | |||
Does the scan tool indicate that this diagnostic failed this ignition? | -- | Go to Diagnostic Aids | ||
Is the ECT sensor below the specified value? | -30°C (-22°F) | |||
Did you find the ECT sensor signal circuit grounded? | -- | |||
6 | Replace the ECT sensor. Refer to Engine Coolant Temperature Sensor Replacement . Is the action complete? | -- | -- | |
7 |
Important:: Program the new PCM. Replace the PCM. Refer to Powertrain Control Module Replacement . Is the action complete? | -- | -- | |
8 |
Does the scan tool indicate that this test ran and passed? | -- | ||
9 | Select the Capture Info option and the Review Info option using the scan tool. Does the scan tool display any DTCs that you have not diagnosed? | -- | Go to the applicable DTC table | System OK |
