DTC P1258 L26

Diagnostic Instructions

DTC Descriptor

DTC P1258: Engine Coolant Over temperature - Protection Mode Active

Circuit/System Description

The engine control module (ECM) or the powertrain control module (PCM) uses the engine coolant temperature (ECT) sensor to monitor the engine for an over-temperature condition. This condition occurs when the coolant temperature is above a calibrated value for a calibrated length of time. The ECM or PCM will disable half of the cylinders by turning OFF the fuel injectors. By disabling half of the cylinders, the ECM or PCM is able to reduce the temperature of the coolant.

Conditions for Running the DTC

Conditions for Setting the DTC

The coolant temperature is more than 132°C (270°F) for more than 10 seconds.

Action Taken When the DTC Sets

Conditions for Clearing the DTC

DTC P1258 is a Type A DTC.

Reference Information

Description and Operation

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

1. If DTC P0480 or P0481 are set, diagnose those DTCs first.
2. Observe the engine coolant level. The engine coolant level should be within the operating range. Refer to Capacities - Approximate Fluid, and Engine Coolant in the Owner's Manual.
3. Ensure that the vehicle has the correct engine coolant with correct concentration and is not old, contaminated, or contains additives. Refer to Recommended Fluids and Lubricants in the Owner's Manual.
4. Inspect the cooling system for the following:

•

Leaks

•	Kinked or pinched hoses, especially at the radiator

•	Loose, missing, or damaged radiator air seals or deflectors

•	Air flow obstructions or bent fins at the radiator or the A/C condenser--Refer to Symptoms - Engine Cooling .

Important: A small delay occurs before the ECM changes the cooling fan speed.

5. Command the cooling fans ON and OFF for L26 or to 100 percent for LS4. The engine cooling fans should turn ON and OFF with each command.

⇒	If the cooling fans do not function as indicated, refer to Cooling Fan Inoperative .

Circuit/System Testing

1. Test the thermostat for correct operation. Refer to Thermostat Diagnosis .
2. Test the engine cooling system for overheating. Refer to Engine Overheating .
3. Inspect the water pump and coolant flow for correct operation. Refer to Water Pump Cleaning and Inspection for the L26 or Water Pump Replacement for the LS4.
4. Inspect the engine for worn/leaking/cracked cylinder heads or engine block. Refer to Coolant in Combustion Chamber and Coolant in Engine Oil for the L26 or Coolant in Combustion Chamber and Coolant in Engine Oil for LS4.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

DTC P1258 LS4

Diagnostic Instructions

DTC Descriptor

DTC P1258: Engine Coolant Over-Temperature - Protection Mode Active

Circuit/System Description

The engine control module (ECM) uses the engine coolant temperature (ECT) sensor to monitor the engine for an over-termperature condition. This condition occurs when the coolant temperature is above a calibrated value for a calibrated length of time. The ECM will disable half of the cylinders by turning OFF the fuel injectors. By disabling half of cylinders, the ECM is able to reduce the temperature of the coolant.

Conditions for Running the DTC

Conditions for Setting the DTC

Coolant temperature more than 132°C (270°F) for greater than 10 seconds.

Action Taken When the DTC Sets

Conditions for Clearing the DTC

DTC P1258 is a Type A DTC.

Reference Information

Description and Operation

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

Important: If DTC P1482 is set, diagnose that DTC first.

1. Observe the engine coolant level. The engine coolant level should be within operating range. Refer to Capacities - Approximate Fluid, and Engine Coolant in the Owner's Manual.
2. Ensure that the vehicle has the correct engine coolant, with correct concentration, and is not old, contaminated or contains additives. Refer to Recommended Fluids and Lubricants in the Owner's Manual.
3. Inspect the cooling system for the following:

•

Leaks

•	Kinked or pinched hoses, especially at the radiator

•	Loose, missing, or damaged radiator air seals or deflectors

•	The radiator and A/C condenser for any air flow obstructions or bent fins--Refer to Symptoms - Engine Cooling .

Important: A small delay occurs before the ECM changes the cooling fan speed.

4. Command the cooling fan speed from 0 percent to 100 percent with a scan tool.

⇒	If the fan speed does not transition with the commanded states, refer to Cooling Fan Inoperative .

Circuit/System Testing

1. Test the thermostat for correct operation. Refer to Thermostat Diagnosis .
2. Test the engine cooling system for overheating. Refer to Engine Overheating .
3. Inspect the water pump and coolant flow for correct operation. Refer to Water Pump Replacement .
4. Inspect the engine for worn/leaking/cracked cylinder heads and engine block. Refer to Coolant in Combustion Chamber and Coolant in Engine Oil .

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.