Circuit Description
An engine coolant temperature (ECT) sensor monitors the temperature of the coolant. This input is used by the engine control module (ECM) for engine control and as an enabling criteria for some diagnostics.
The air flow coming into the engine is accumulated and used to determine if the engine has been driven within 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 regulating temperature of the thermostat, diagnostics that use ECT as enabling criteria may not run when expected.
This DTC will run continuously. If the ECM detects the calibrated amount of air flow and engine run time at any time is equal to a predetermined value, and the ECT has not met the minimum calibrated thermostat regulating temperature, DTC P0128 sets.
Conditions for Running the DTC
| • | DTCs P0116, P0117, P0118, P0125, or P0500 are not set. |
| • | The startup ECT is less than 50.25°C (122.45°F). |
| • | The start-up intake air temperature (IAT) is between -9.75 and +50.25°C (+14.45 to +122.45°F). |
| • | Fuel cutoff is not active. |
| • | The engine is running at more than 960 RPM. |
| • | The vehicle is moving at more than 15 km/h (9 mph). |
| • | More than 3 kg of air has passed through the engine. |
| • | A block heater is not detected or the DTC is delayed for 25 seconds. |
Conditions for Setting the DTC
The PCM detects that:
| • | The calibrated amount of engine run time at any time has been met |
| • | The calibrated amount of engine air flow at any time has been met |
| • | The actual ECT is 11°C (19°F) less than a predetermined calibrated ECT should be. |
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. |
Step | Action | Values | Yes | No | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Engine Controls Connector End Views or Engine Control Module Connector End Views | ||||||||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |||||||
2 |
Important: The cooling fans are commanded ON when certain engine coolant temperature (ECT) DTCs are set. Is the cooling system coolant low? | -- | Go to Cooling System Draining and Filling in Engine Cooling | Go to Step 3 | ||||||
3 | Test and verify the proper operation of the thermostat. Refer to Thermostat Diagnosis in Engine Cooling. Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 4 | ||||||
4 |
Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 5 | ||||||
5 | Measure the voltage from the signal circuit of the ECT sensor to a good ground with a DMM. Refer to Circuit Testing in Wiring Systems. Is the voltage within the specified range? | 4.8-5.2 V | Go to Step 6 | Go to Step 8 | ||||||
6 | Measure the voltage from the signal circuit of the ECT sensor to the low reference circuit of the ECT sensor with a DMM. Refer to Circuit Testing in Wiring Systems. Is the voltage within the specified range? | 4.8-5.2 V | Go to Step 9 | Go to Step 7 | ||||||
7 | Test the ECT sensor low reference circuit for high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 11 | ||||||
8 | Test the ECT sensor signal circuit for high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 11 | ||||||
9 |
Is the resistance measurement of the ECT sensor within the specified range? | -- | Go to Step 10 | Go to Step 12 | ||||||
10 | Install the ECT sensor. Refer to Engine Coolant Temperature Sensor Replacement . Is the action complete? | -- | Go to Intermittent Conditions | -- | ||||||
11 | Test for an intermittent and for a poor connection at the ECM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 13 | ||||||
12 | Replace the ECT sensor. Refer to Engine Coolant Temperature Sensor Replacement . Did you complete the replacement? | -- | Go to Step 14 | -- | ||||||
13 | Replace the ECM. Refer to Engine Control Module Replacement . Did you complete the replacement? | -- | Go to Step 14 | -- | ||||||
14 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 15 | ||||||
15 | Observe the Capture Info. with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK | |||||||
