p0128
Moderate
Mazda · Sedans
Coolant Thermostat (Coolant Temp Regulating Valve) Performance
Quick Answer
Error code P0128 on your Mazda 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
Monitor coolant temperature with scanner
2
Feel radiator hoses for temperature change
3
Replace thermostat if stuck open
4
Flush cooling system to remove blockages
5
Clear codes and verify normal operating temperature
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
Temperature sensor
Gaskets
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