Chevy Trailblazer P0128 is an OBD-II (On-Board Diagnostics II) trouble code that indicates a problem with the engine coolant temperature (ECT) sensor or thermostat. Specifically, it indicates that the engine coolant temperature is below the thermostat regulating temperature for too long. This code is triggered when the Powertrain Control Module (PCM) determines that the coolant temperature has not reached the proper operating temperature within a specified time frame after engine start-up.
Some common causes of P0128 in a Chevy Trailblazer include:
- Faulty engine coolant temperature sensor
- Faulty thermostat
- Low coolant level
- Clogged or dirty coolant system
- Failed water pump
- Failed radiator fan
- Malfunctioning PCM
To diagnose the problem, a mechanic will typically use a scan tool to retrieve the diagnostic trouble codes and perform a visual inspection of the cooling system. They may also test the ECT sensor, thermostat, and related components using a multimeter or other diagnostic equipment.
Once the root cause of the problem is identified, the mechanic will perform the necessary repairs, such as replacing the faulty component or flushing and filling the coolant system. After the repairs are complete, they will clear the diagnostic trouble codes and verify that the P0128 code is no longer present.