Engine Coolant Overtemperature Protection Active (BMW)
What does P1255 mean?
The P1255 code means the vehicle's onboard diagnostic system has detected: Engine Coolant Overtemperature Protection Active (BMW). This is a critical severity code.
Common Symptoms
- Check Engine Light on
- Temperature warning on dashboard
- Engine power severely reduced
- Engine running in limp mode
- Cooling fans running at maximum speed
Probable Causes (Ranked by Likelihood)
- Coolant thermostat stuck closed Very High
- Failed electric water pump High
- Coolant leak causing low coolant level Moderate
- Radiator partially blocked or clogged Moderate
- Cooling fan module failure Low
Step-by-Step Diagnostic Procedure
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Check coolant level in the expansion tank
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Scan for additional cooling system codes
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Test thermostat operation by monitoring temperature during warmup
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Verify electric water pump with scan tool activation test
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Inspect radiator and hoses for leaks or blockage
Frequently Asked Questions
What does overtemperature protection mean?
P1255 means the engine exceeded safe temperature and the PCM activated protection mode to prevent damage. This is a serious condition.
Is the electric water pump a known BMW issue?
Yes. BMW electric water pumps on N51, N52, N54, and N55 engines are a known failure item, typically failing between 60,000-100,000 miles.
Can I drive with P1255?
No. Pull over safely and turn off the engine. Continuing to drive with an overheating engine can cause warped heads and blown head gaskets.