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p0128
Easy Fix
BMW · SUVs
Coolant Thermostat Below Regulating Temperature
Quick Answer
Error code P0128 on your BMW SUVs means: Coolant Thermostat Below Regulating Temperature. This is usually fixable — see the step-by-step guide below.
Affected Models
Applies to all models
X1 M35i 2024X1 xDrive28i 2024X3 M 2024X3 M40i 2024X3 xDrive30i 2024X5 M 2024X5 M60i 2024X5 xDrive40i 2024X5 xDrive50e 2024X6 M 2024X6 M60i 2024X6 xDrive40i 2024X7 M60i 2024X7 xDrive40i 2024iX M60 2024iX xDrive50 2024X1X3 MX3X5 MX5X6X7iX
Likely Causes
  1. Thermostat stuck in the open position
  2. Faulty engine coolant temperature (ECT) sensor
  3. Low coolant level
  4. Cracked thermostat housing or failed gasket
  5. Malfunctioning electric thermostat heater element
How to Fix It
1
Check coolant level and inspect for visible leaks
2
Monitor coolant temperature during warm-up with a scan tool
3
Test the ECT sensor with a multimeter
4
Replace the thermostat and housing gasket
5
Bleed the cooling system and verify the engine reaches operating 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
Related Error Codes
P0171P0174P0300P0301P0335
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