Circuit Description
An engine coolant temperature (ECT) sensor monitors the temperature of the coolant. The fuel burned since start up is used to determine if the vehicle has been driven within the conditions that would allow the engine coolant to heat up normally to the thermostat regulating temperature. If the coolant temperature does not increase normally, or does not reach the regulating temperature of the thermostat, the diagnostics that use engine coolant temperature as enabling criteria, may not run when expected.
This DTC will only run once per ignition cycle until a Pass, Fail or Disable condition exists.
If the engine coolant fails to reach a preset target temperature before the calculated amount of fuel is burned, DTC P0128 will set.
Conditions for Running the DTC
| • | DTCs P0112, P0113, P0117 or P0118 are not set. |
| • | The engine coolant startup temperature is less than 51°C (124°F). |
| • | The ambient air temperature is more than -7°C (+19°F). |
| • | The engine run time is more than 925 seconds. |
| • | The fuel burned since startup is more than 8.5 million cubic millimeters. |
| • | The total idle time is less than 300 seconds. |
| OR |
| • | DTCs P0112, P0113, P0117 or P0118 are not set. |
| • | The engine coolant startup temperature is between 51°-65°C (124°-149°F). |
| • | The ambient air temperature is more than -7°C (+19°F). |
| • | The engine run time is more than 500 seconds. |
| • | The fuel burned since startup is more than 5 million cubic millimeters. |
| • | The total idle time is less than 150 seconds. |
Conditions for Setting the DTC
The ECM detects the following:
| • | The calibrated amount of engine run time has been met. |
| • | The calibrated amount of fuel has been burnt. |
| • | The calibrated ECT of 72°C (162°F) has not been met. |
Action Taken When the DTC Sets
| • | The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails. |
| • | The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame/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
| • | DTC P0128 is designed to detect a faulty thermostat. |
| • | A skewed low ECT sensor can cause a DTC P0128 to set. |
| • | If an intermittent condition is suspected refer to Intermittent Conditions . |
| • | Using Freeze Frame/Failure Records may aid in determining the conditions under which the failure occurred. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step tests for excessive resistance in the ECT circuit.
-
This step tests for a skewed sensor through the range of temperatures affecting this DTC.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Engine Control Module Connector End Views or Engine Controls Connector End Views | ||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |
2 | Is the cooling system coolant low? | -- | Go to Loss of Coolant in Engine Cooling | Go to Step 3 |
Is the ECT sensor parameter more than the specified value? | 146°C (294°F) | Go to Step 7 | Go to Step 4 | |
4 |
Is the ECT sensor parameter more than the specified value? | 146°C (294°F) | Go to Step 5 | Go to Step 6 |
5 | Test the ECT sensor low reference circuit for a high resistance or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 10 | Go to Diagnostic Aids |
6 | Test the ECT sensor signal circuit for a high resistance or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 10 | Go to Diagnostic Aids |
Does the resistance and temperature closely match the Temperature vs Resistance Table? | 10°-90°C (50°-194°F) | Go to Step 8 | Go to Step 9 | |
8 | Install the ECT sensor. Refer to Engine Coolant Temperature Sensor Replacement . Did you complete the action? | -- | Go to Engine Fails To Reach Normal Operating Temperature in Engine Cooling | -- |
9 | Replace the ECT sensor. Refer to Engine Coolant Temperature Sensor Replacement . Did you complete the replacement? | -- | Go to Step 10 | -- |
10 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 11 |
11 | Observe the Capture Info with a scan tool. Are there any DTC's that have not been diagnosed? | -- | System OK | |
