Engine Coolant Overtemperature -- Protection Mode Active (GM)
What does P1258 mean?
The P1258 code means the vehicle's onboard diagnostic system has detected: Engine Coolant Overtemperature -- Protection Mode Active (GM). This is a critical severity code.
Common Symptoms
- Check Engine Light on
- Engine temperature gauge reads hot
- Reduced engine power warning
- Engine shuts down cylinders to cool down
- Coolant leak or low coolant warning
Probable Causes (Ranked by Likelihood)
- Low coolant level from a leak Very High
- Failed thermostat stuck closed High
- Faulty water pump Moderate
- Clogged radiator Moderate
- Blown head gasket causing coolant loss Low
Step-by-Step Diagnostic Procedure
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Check coolant level -- add coolant if low and inspect for leaks
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Verify the cooling fans are operating when the engine is hot
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Test the thermostat -- it should open at the specified temperature
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Check the water pump for leaks and proper circulation
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Perform a combustion gas test to check for a blown head gasket
Frequently Asked Questions
Can I drive with code P1258?
No. Stop driving immediately if the engine is overheating. Continued driving can cause severe engine damage including a warped cylinder head, blown head gasket, or seized engine.
What causes P1258?
The engine has overheated and the PCM has activated protection mode (shutting down cylinders to reduce heat). The most common causes are low coolant from a leak, a stuck thermostat, or a failed water pump.
What is GM engine protection mode?
When the engine reaches a dangerous temperature, the PCM disables fuel to some cylinders to reduce heat production. This causes the engine to run rough but prevents catastrophic damage. Always pull over and shut off the engine.