p0128
Moderate
Cadillac · Sedans
Coolant Thermostat (Coolant Temp Regulating Valve) Performance
Quick Answer
Error code P0128 on your Cadillac Sedans means: Coolant Thermostat (Coolant Temp Regulating Valve) Performance. This is usually fixable — see the step-by-step guide below.
Affected Models
Likely Causes
How to Fix It
1
Check coolant level and top off if needed
2
Monitor coolant temperature with scan tool
3
Feel upper radiator hose for temperature change
4
Test thermostat operation
5
Replace thermostat if it's 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
Coolant
Radiator hose
Coolant temperature sensor
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