p0128
Easy Fix
Audi · SUVs
Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)
Quick Answer
Error code P0128 on your Audi SUVs means: Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature). This is usually fixable — see the step-by-step guide below.
Affected Models
Likely Causes
How to Fix It
1
Monitor engine coolant temperature via scan tool during a cold start warm-up
2
Compare coolant temperature rise time to manufacturer specification
3
Verify the correct thermostat part number is installed for the engine application
4
Test the coolant temperature sensor with a multimeter and compare to a temperature chart
5
Replace the thermostat if the engine does not reach operating temperature within spec
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
Coolant
Coolant temperature sensor
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