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2003 Chevrolet Trailblazer 4.2L Inline Six - OBD2 Code P0128: Coolant Temperature Below Thermostat Regulation

Model: 2003 Chev Trailblazer Fault Code: P0128 Posted: 2014-04-07 08:23

My 2003 Chevrolet Trailblazer with a 4.2L inline-six engine is showing OBD2 diagnostic code P0128, which indicates the engine coolant temperature is below the thermostat's required operating temperature. This fault code typically occurs when the thermostat fails to open properly or when there is insufficient coolant flow, leading to poor engine warm-up performance. The issue may also stem from a malfunctioning thermostat, low coolant levels, or a blocked radiator. The most common fix involves replacing the thermostat with a 195°F (90°C) model specifically designed for this engine configuration.

Related fault codes
P0128
Comments (2)
Anonymous 2014-04-07 08:29

Make sure to inspect and replace the thermostat — it must be a 195-degree unit. This is a common fix for P0128 in 2003 Chevrolet Trailblazers with 4.2L engines. For more details, see: http://www.obd-codes.com/p0128

Anonymous 2014-07-23 21:03

Did you resolve the issue? What was the root cause? I own a 2004 Chevrolet Trailblazer with the same P0128 code and am looking for confirmation on whether thermostat replacement fixed it.