p0128
Moderate
Subaru · SUVs & Crossovers
Coolant Thermostat (Coolant Temp Malfunction)
Quick Answer
Error code P0128 on your Subaru SUVs & Crossovers means: Coolant Thermostat (Coolant Temp Malfunction). This is usually fixable — see the step-by-step guide below.
Affected Models
Likely Causes
How to Fix It
1
Connect OBD-II scanner and monitor coolant temperature
2
Check actual coolant temperature with infrared thermometer
3
Verify thermostat operation by monitoring warm-up time
4
Inspect for coolant leaks
5
Test coolant temperature sensor resistance
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
OBD-II scanner
Thermostat
Coolant temperature sensor
Engine coolant
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