P0128
DTC P0128
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 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, diagnostics that use ECT as enabling criteria, may not run when expected. This DTC will only run once per ignition cycle within the enabling conditions.
If the ECM 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 P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0120, P0121, P0122, P0123, P0220, P0222, P0223, P0502, P0503 are not present.
- The start up engine coolant temperature is less than 70°C (158°F).
- The intake air temperature (IAT) sensor parameter is more than -7°C (+19°F).
- The engine is running between 120-1,370 seconds.
- The vehicle speed is more than 8 km/h (5 mph) for more than 2.5 kilometers (1.5 miles).
- The mass air flow (MAF) is between 12-50 g/s with the average more than 5 g/s.
- The above conditions are met for a time based on airflow.
- DTC P0128 runs once per trip.
CONDITIONS FOR SETTING THE DTC
The minimum engine coolant temperature of 75°C (167°F) has not been met within a specified amount of time and total airflow.
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.
TEST
