P0128
DTC P0128
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.
TEST
