DTC P1258 V6

Diagnostic Instructions

DTC Descriptor

DTC P1258: Engine Coolant Overtemperature - 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

The EM detects that engine coolant temperature is greater than 136°C (277°F) for more than 1 second or a cumulative time of 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 DTCs P0480, P0481, P0691, P0692, P0693, or P0694 are set, diagnose those DTCs 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:

•	Cooling system 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 fans in both low and high speed.

⇒	If the cooling fans do not operate in both speeds, refer to Cooling Fan Inoperative.

5. Test the thermostat for correct operation. Refer to Thermostat Diagnosis.
6. Test the engine cooling system for overheating. Refer to Engine Overheating.
7. Inspect the water pump and coolant flow for correct operation. Refer to Water Pump Replacement.
8. Inspect the engine mechanical 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.

DTC P1258 with RPO LC3 or LH2

Diagnostic Instructions

DTC Descriptor

DTC P1258: Engine Coolant Overtemperature - Protection Mode Active

Circuit/System Description

The engine control module (ECM) uses the engine coolant temperature (ECT) sensor to monitor the engine for an overtermperature 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 131°C (267.8°F) for more than 7 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 DTCs P0480 or P0481 are set, diagnose those DTCs 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:

•	Cooling system 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 fans in both low and high speed.

⇒	If the cooling fans do not operate in both speeds, 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 mechanical for worn/leaking/cracked cylinder heads and engine block. Refer to Coolant in Combustion Chamber and Coolant in Engine Oil for the 4.4L engine, or Coolant in Combustion Chamber and Coolant in Engine Oil for the 4.6L engine.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.