p0128
Easy Fix
Volkswagen · SUVs
Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)
Quick Answer
Error code P0128 on your Volkswagen SUVs means: Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature). This is usually fixable — see the step-by-step guide below.
Affected Models
Applies to all models
CAID4ID6B25N5N-LWBCRAtlas Cross Sport SE 2024Atlas Cross Sport SEL 2024Atlas Cross Sport SEL R-Line 2024Atlas SE 2024Atlas SEL 2024Atlas SEL Premium R-Line 2024ID.4 Pro 2024ID.4 Pro S 2024ID.4 Pro S Plus 2024ID.4 Standard 2024Taos S 2024Taos SE 2024Taos SEL 2024Tiguan S 2024Tiguan SE 2024Tiguan SEL 2024Tiguan SEL R-Line 2024
Likely Causes
How to Fix It
1
Monitor coolant temperature with a scan tool during warm-up; if it never reaches 190°F, the thermostat is likely stuck open
2
Compare the coolant temperature sensor reading to an infrared thermometer reading on the engine
3
Remove the thermostat and inspect it for damage or test it in heated water for proper opening temperature
4
Check the cooling fan operation; verify it is not running at cold start when it should not be
5
Replace the thermostat and housing assembly; use OEM parts for proper temperature regulation
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 with housing
Coolant temperature sensor
Coolant (G12/G13 spec)
Thermostat O-ring or gasket
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