p0128
Easy Fix
Chevrolet · Trucks
Coolant Thermostat Below Regulating Temperature
Quick Answer
Error code P0128 on your Chevrolet Trucks means: Coolant Thermostat Below Regulating Temperature. This is usually fixable — see the step-by-step guide below.
Affected Models
Applies to all models
CK15706Colorado LT 2024Colorado Trail Boss 2024Colorado WT 2024Colorado Z71 2024Colorado ZR2 2024Silverado 1500 Custom 2024Silverado 1500 High Country 2024Silverado 1500 LT 2024Silverado 1500 LT Trail Boss 2024Silverado 1500 LTZ 2024Silverado 1500 RST 2024Silverado 1500 WT 2024Silverado 1500 ZR2 2024Silverado 2500HD High Country 2024Silverado 2500HD LT 2024Silverado 2500HD LTZ 2024Silverado 2500HD WT 2024CL14543CS10403CK10743CK10543CK20943CK30943CK10906
Likely Causes
How to Fix It
1
Check engine coolant level and top off if low; inspect for leaks
2
Monitor engine coolant temperature with a scan tool during warm-up
3
Verify the cooling fan is not running continuously at cold start
4
Remove and test the thermostat by heating it in water and checking opening temperature
5
Replace the thermostat if it opens below the rated temperature or is stuck open
Pro Tip
This is a common issue that most users can resolve without specialized tools. Try the first step before moving on to more complex solutions.
Parts You May Need
Thermostat
Thermostat housing gasket
Engine coolant
ECT sensor (if faulty)
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