Circuit Description
An engine coolant temperature (ECT) sensor monitors the temperature of the coolant. This input is used by the powertrain control module (PCM) 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.
If the PCM detects the calibrated amount of air flow and engine run time have been met, and the ECT has not met the minimum thermostat regulating temperature, DTC P0128 sets.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0128 Engine Coolant Temperature (ECT) Below Thermostat Regulating Temperature
Conditions for Running the DTC
| • | DTCs P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0130, P0131, P0132, P0133, P0134, P0171, P0172, P0201, P0202, P0203, P0204, P0300, P0301-P0304, P0335, P0336, P0442, P0446, P0452, P0453, P0455, P0480, P0496, P0502 and P0503 for automatic transmission only, P0601, P0602, P0604, P0606, P0621, P1133, or P1683 are not set. |
| • | The engine run time is between 30 seconds and 30 minutes. |
| • | The minimum intake air temperature (IAT) is more than -7°C (19°F). |
| • | The engine coolant temperature at start up is less than 70°C (158°F). |
| • | The average airflow is more than 15 g/s. |
| • | The vehicle has traveled more than 2.4 km (1.5 mi) over 40 km/h (25 mph). |
| • | This DTC runs once per ignition cycle when the above conditions are met. |
Conditions for Setting the DTC
| • | The calibrated amount of engine run time has been met. |
| • | The calibrated amount of engine air flow has been met. |
| • | The calibrated ECT of 75°C (167°F) has not been met. |
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 Powertrain Control Module Connector End Views | ||||||||||
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information | ||||||
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 | Test for an intermittent and for a poor connection at the powertrain control module (PCM). 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 6 | ||||||
6 | Measure the resistance of the ECT sensor signal circuit between the sensor and the PCM with a DMM. Refer to Circuit Testing in Wiring Systems. Is the resistance within the specified range? | 0-10 ohms | Go to Step 7 | Go to Step 10 | ||||||
7 | Measure the resistance of the ECT sensor low reference circuit between the sensor and the PCM with a DMM. Refer Circuit Testing in Wiring Systems. Is the resistance within the specified range? | 0-10 ohms | Go to Step 8 | Go to Step 11 | ||||||
8 |
Is the resistance measurement of the ECT sensor within the specified range? | -- | Go to Step 9 | Go to Step 12 | ||||||
9 | Install the ECT sensor. Refer to Engine Coolant Temperature Sensor Replacement . Is the action complete? | -- | Go to Step 13 | -- | ||||||
10 | Repair the high resistance in the ECT sensor signal circuit. Refer to Wiring Repairs in Wiring Systems . Did you complete the repair? | -- | Go to Step 14 | -- | ||||||
11 | Repair the high resistance in the ECT sensor low reference circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 14 | -- | ||||||
12 | Replace the ECT sensor. Refer to Engine Coolant Temperature Sensor Replacement . Did you complete the replacement? | -- | Go to Step 14 | -- | ||||||
13 | Replace the PCM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming. 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? | -- | Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information | System OK | ||||||
