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P1258

Engine Coolant Overtemperature Protection Mode Active.

  • GMC
  • Powertrain
  • Manufacturer code
  • High severity

How this code is built

P
SystemPowertrain
1
Defined byThe manufacturer
2
AreaFuel and air metering (injector circuit)
58
FaultThe specific fault in that area

What it means

On a GMC, P1258 means the engine control module has activated its engine coolant overtemperature protection mode because the engine got too hot. In this mode the ECM typically cuts fuel to some cylinders, so the engine runs on fewer cylinders and the air passing through the idle cylinders helps to cool it. The code is set after the coolant temperature sensor reading went above the calibrated limit, so it points to an overheating problem rather than a fault in the sensor alone.

Symptoms

  • Temperature gauge reading high or warning light or message showing
  • Engine running rough, misfiring or with noticeably reduced power
  • Engine cooling fan running constantly or at high speed
  • Steam, coolant smell or visible coolant loss
  • Check engine light on, possibly with other coolant temperature codes stored

Possible causes

  • Low coolant level from a leak (hoses, radiator, water pump, heater core or gaskets)likely
  • Cooling fan not working (fan motor, relay, fuse or control circuit)likely
  • Stuck thermostat or air trapped in the cooling systemlikely
  • Blocked radiator or restricted airflow through the radiator and condenserpossible
  • Weak or failing water pump, or slipping drive beltpossible
  • Faulty coolant temperature sensor or wiring giving a false high readingpossible
  • Head gasket failure or cracked cylinder head forcing combustion gases into the coolantrare

How to diagnose

  1. Read all stored codes and freeze frame data, noting coolant temperature, engine load and speed when the code set, and check for related coolant sensor or fan codes
  2. Check the coolant level and condition once the engine is fully cold, and look for leaks, oil contamination or a rusty or sludgy appearance
  3. Inspect the radiator, condenser and fan shroud for blockage, damage or missing air ducting, and check the drive belt condition and tension
  4. Check that the cooling fans come on when commanded, and check the related fuses, relays, connectors and wiring
  5. Compare the scan tool coolant temperature reading with an independent temperature measurement of the engine to confirm the sensor is accurate
  6. Check that the upper and lower radiator hoses become hot at the right time, which indicates the thermostat is opening and coolant is circulating
  7. Pressure test the cooling system and test for combustion gases in the coolant to rule out a head gasket leak
  8. Check for water pump operation and flow, as the procedure varies by model and engine

How to fix

  • Repair any coolant leak, refill with the correct coolant mixture and bleed air from the system following the model-specific procedure
  • Repair or replace the cooling fan motor, relay, fuse or wiring as found faulty
  • Replace a stuck thermostat or a failing water pump, and renew the drive belt if worn or slipping
  • Clean or replace a blocked radiator and restore any missing air ducting
  • Replace the coolant temperature sensor or repair its wiring or connector if the reading is proved false
  • Repair the engine, such as a head gasket or cylinder head, if testing confirms combustion gases in the coolant

Can I keep driving?

High severity

Do not keep driving the vehicle. Stop safely, switch off and let the engine cool, as continued overheating can cause severe and expensive engine damage, and have the cause found before further use.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.

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