Circuit Description
The engine coolant temperature (ECT) sensor contains a thermistor which changes resistance based on the temperature. The ECT sensor is located in the coolant crossover pipe at the center rear of the engine. The ECT sensor has a signal circuit and a ground circuit. The engine control module engine control module (ECM) applies a voltage, about 5 volts, on the signal circuit to the sensor. The ECM monitors the changes in this voltage that are caused by the changes in the resistance of the sensor in order to determine the engine coolant temperature.
When the engine coolant is cold, the sensor resistance is high, and the ECM will sense a high signal voltage or low temperature. When the engine coolant is warm, the sensor resistance is low. This causes the ECM to sense a low signal voltage or high temperature.
When the ECM senses a signal voltage outside of the normal operating range of the sensor, this diagnostic trouble code (DTC) will set.
Conditions for Running the DTC
The ignition is ON.
Conditions for Setting the DTC
The ECT signal voltage indicates an ECT that is more than 139°C (282°F).
OR
The ECT signal voltage indicates an ECT that is at -40°C (-40°F).
Action Taken When the DTC Sets
| • | The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails. |
| • | The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records. |
Conditions for Clearing the MIL/DTC
| • | The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail. |
| • | A current DTC, Last Test Failed, clears when the diagnostic runs and passes. |
| • | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic. |
| • | Clear the MIL and the DTC with a scan tool. |
Diagnostic Aids
| • | Use the J 35616 Connector Test Adapter Kit for any test that requires probing the ECM harness connector or a component harness connector. Using this kit prevents damage to the harness or component terminals. Refer to Using Connector Test Adapters in Wiring Systems. |
| • | Check for poor connections at the ECM or at the component. |
| • | Use the Temperature Versus Resistance - Engine Coolant Temperature Sensor table may be used in order to test the ECT sensor at various temperature levels. This will aid in determining if the sensor is skewed. A skewed sensor may cause a driveability concern. |
| • | For intermittents, refer to Symptoms - Engine Controls , Preliminary Checks. |
| • | If other DTCs are set that share the same ground circuit, test the point where the circuits splice and where the circuit connects to the ECM for opens or high resistance. |
| • | If the engine has been allowed to sit overnight, the engine coolant temperature and the intake air temperature (IAT) values should display within a few degrees of each other. If the temperatures are not within 3°C (5°F), refer to Temperature Versus Resistance - Engine Coolant Temperature Sensor . |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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Turn ON the engine and monitor the ECT on the scan tool. The ECT sensor temperature should rise steadily with the temperature of the engine.
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Using the Freeze Frame data may aid in locating an intermittent condition. If the DTC cannot be duplicated, review the information in the Freeze Frame. Try to operate the vehicle within the same Freeze Frame conditions, the RPM, the MAF, the vehicle speed, the temperature, that were noted. This process may help to recreate the malfunction.
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This step tests for proper operation of the circuit in the high voltage range.
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This step tests for a short to voltage on the ECT sensor signal circuit.
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This step tests the integrity of the reference ground circuit through the ECM to battery ground. Make sure the ECM has shut down prior to measuring the reference ground circuit resistance. This can be verified by the loss of communication on the scan tool. Do not use a test lamp to test the continuity of the reference ground circuit. Damage to the ECM will result.
-
Perform the idle learn procedure when replacing the ECM or throttle body.
Step | Action | Values | Yes | No | ||||
|---|---|---|---|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |||||
Is the ECT near the specified value? | 139°C (282°F) | Go to Step 6 | Go to Step 3 | |||||
3 | Is the ECT at the specified value? | -40°C (-40°F) | Go to Step 8 | Go to Step 4 | ||||
4 |
Does the harness movement affect the ECT value? | -- | Go to Step 15 | Go to Step 5 | ||||
Did the DTC fail this ignition? | -- | Go to Step 6 | Go to Diagnostic Aids | |||||
Is the ECT at the specified value? | -40°C (-40°F) | Go to Step 19 | Go to Step 7 | |||||
7 |
Is continuity indicated? | -- | Go to Step 16 | Go to Step 21 | ||||
Is the voltage more than the specified value? | 5.2 V | Go to Step 18 | Go to Step 9 | |||||
9 | Jumper the ECT signal circuit to a known good ground. Is the ECT near the specified value? | 139°C (282°F) | Go to Step 11 | Go to Step 10 | ||||
10 |
Is the resistance less than the specified value? | 5 ohms | Go to Step 21 | Go to Step 17 | ||||
|
Important: Make sure the ECM has shut down prior to measuring the reference ground circuit resistance. This can be verified by the loss of communication on the scan tool.
Important: Do not use a test lamp to test the continuity of the reference ground circuit. Damage to the ECM will result. Is the resistance less than the specified value? | 5 ohms | Go to Step 19 | Go to Step 12 | |||||
12 |
Did you find and correct the condition? | -- | Go to Step 23 | Go to Step 13 | ||||
13 | Measure the resistance from the ground stud at the ECM bracket to battery ground. Is the resistance less than the specified value? | 5 ohms | Go to Step 21 | Go to Step 14 | ||||
14 | Repair the open or high resistance in the ECM ground circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 23 | -- | ||||
15 | Repair the harness or connections as necessary. Refer to Connector Repairs or Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 23 | -- | ||||
16 | Repair the ECT signal circuit shorted to ground. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 23 | -- | ||||
17 | Repair the open or high resistance in the ECT signal circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 23 | -- | ||||
18 | Repair the short to voltage in the ECT signal circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 23 | -- | ||||
19 |
Did you find and correct the condition? | -- | Go to Step 23 | Go to Step 20 | ||||
20 | Replace the ECT sensor. Refer to Engine Coolant Temperature Sensor Replacement . Did you complete the replacement? | -- | Go to Step 23 | -- | ||||
21 |
Did you find and correct the condition? | -- | Go to Step 23 | Go to Step 22 | ||||
|
Important:
Replace the ECM. Refer to Engine Control Module Replacement . Did you complete the action? | -- | Go to Step 23 | -- | |||||
23 |
Does the DTC run and pass? | -- | Go to Step 24 | Go to Step 2 | ||||
24 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |||||
