p0128
Easy Fix
BMW · Sedans
Coolant Thermostat Below Regulating Temperature
Quick Answer
Error code P0128 on your BMW Sedans means: Coolant Thermostat Below Regulating Temperature. This is usually fixable — see the step-by-step guide below.
Affected Models
Applies to all models
Likely Causes
How to Fix It
1
Check coolant level and inspect for leaks at the thermostat housing
2
Monitor coolant temperature with a scan tool during warm-up to verify slow heating
3
Test the engine coolant temperature sensor with a multimeter
4
Replace the thermostat and housing gasket
5
Refill and bleed the cooling system and verify proper warm-up temperature
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
Engine coolant
Coolant temperature sensor
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