Why suddenly would my car start doing this?
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 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 ECT as enabling criteria may not run when expected.
This DTC will only run once per ignition cycle within the enabling conditions. 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.
Conditions for Running the DTC
DTCs P0101, P0102, P0103, P0112, P0113, P0116, P0117, P0118, P0125, P0502, P0503 are not present.
The startup ECT is less than 75°C (167°F).
The intake air temperature (IAT) is more than -7°C (+19°F).
The engine run time is between 30-1,800 seconds.
The vehicle is driven more than 0.8 kilometers (0.5 miles) at more than 8 km/h (5 mph).
Conditions for Setting the DTC
The PCM detects that:
The calibrated amount of engine run time has been met.
The calibrated amount of engine air flow has been met.
The calibrated vehicle speed and distance have been met.
The calibrated ECT of 80°C (176°F) has not been met.
IN OTHER WORDS, BAD T-STAT OR ENGINE COOLANT TEMP SENSOR
