P1258

DTC P1258

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Diagnostic System Check - Vehicle) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Strategy Based Diagnosis) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Diagnostic Procedure Instructions) provides an overview of each diagnostic category.

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

The engine is operating.

Conditions for Setting the DTC

All V8

The coolant temperature is warmer than 129°C (264°F) for greater than 10 seconds.

6.0L-Hybrid

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

Action Taken When the DTC Sets

* DTC P1258 is a Type A DTC.
* The engine will operate in the Overheated Engine Protection Operating Mode.
* The engine coolant temperature indicator lamp, if equipped, will illuminate.
* The driver information center (DIC), if equipped, may display a message.
* If the protection mode is active and an ECT sensor DTC sets, the protection mode will activate during the next drive cycle until the ECT sensor DTC runs and passes.

Conditions for Clearing the DTC

DTC P1258 is a Type A DTC.

Reference Information
Description and Operation

* Cooling System Description and Operation (Cooling System)
* Instrument Cluster Description and Operation (Instrument Cluster)
* Indicator/Warning Message Description and Operation (Indicator/Warning Message)
* Audible Warnings Description and Operation (Audible Warnings)

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions (Powertrain Diagnostic Trouble Code (DTC) Type Definitions)
Scan Tool Reference

Control Module References (Programming and Relearning) for scan tool information

Circuit/System Verification

Note: If DTC P0480, P0481, or P0482 is set, diagnose that DTC first.

1. Observe the engine coolant level. The engine coolant level should be within operating range. Refer to Cooling System Draining and Filling (Vac-N-Fill) (Service and Repair)Cooling System Draining and Filling (Static Fill) (Service and Repair)
2. Ensure that the vehicle has the correct engine coolant, with correct concentration, and is not old, contaminated or contains additives. Refer to Cooling System Draining and Filling (Vac-N-Fill) (Service and Repair)Cooling System Draining and Filling (Static Fill) (Service and Repair)
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 (Symptoms - Engine Cooling).

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

4. Command the cooling fans ON in each available speed with a scan tool.

• If the cooling fans are inoperative in any of the commanded states, refer to Cooling Fan Inoperative (without HP2) (Cooling Fan Inoperative)Cooling Fan Inoperative (with HP2) (Cooling Fan Inoperative).

Circuit/System Testing

1. Test the thermostat for correct operation. Refer to Thermostat Diagnosis (Thermostat Diagnosis).
2. Test the engine cooling system for overheating. Refer to Engine Overheating (Engine Overheating).
3. Inspect the water pump and coolant flow for correct operation. Refer to Water Pump Replacement (LU3) (Service and Repair)Water Pump Replacement (LMM) (Service and Repair)Water Pump Replacement (V8) (Service and Repair).
4. Inspect the engine for worn/leaking/cracked cylinder heads and engine block. Refer to Coolant in Combustion Chamber (Coolant in Combustion Chamber) and Coolant in Engine Oil (Coolant in Engine Oil).

Repair Instructions

Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.