p0128
Moderate
GMC · SUVs
Coolant Thermostat (Coolant Temp Regulation)
Quick Answer
Error code P0128 on your GMC SUVs means: Coolant Thermostat (Coolant Temp Regulation). This is usually fixable — see the step-by-step guide below.
Affected Models
Likely Causes
How to Fix It
1
Monitor coolant temperature readings
2
Perform cooling system pressure test
3
Inspect thermostat operation
4
Check temperature sensor readings
5
Replace thermostat if stuck
Pro Tip
This fix requires some technical knowledge. If you're unsure about any step, consider contacting support or a qualified technician.
Parts You May Need
Thermostat assembly
Coolant
Water pump gasket
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