P1258

DTC P1258 (LZG-3.9L Flex Fuel)

Diagnostic Instructions

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

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-temperature condition. This condition occurs when the coolant temperature is above a calibrated value. The ECM will alternately disable 2 groups of cylinders by turning OFF the fuel injectors. By switching between the 2 groups of cylinders, the ECM is able to reduce the temperature of the coolant.

Conditions for Running the DTC

* The engine is running.
* DTC P0116, P0117, P0118, or P0128 is not set.

Conditions for Setting the DTC

The coolant temperature is more than 131°C (267.8°F) for more than 7 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 instrument panel (I/P) will illuminate the coolant temperature indicator lamp and the driver information center (DIC), if equipped, may display a message.

Conditions for Clearing the DTC

DTC P1258 is a Type A DTC.

Reference Information
Description and Operation

* Cooling Fan Description and Operation (Description and Operation)
* Instrument Cluster Description and Operation (Description and Operation)
* Indicator/Warning Message Description and Operation (Indicator/Warning Message Description and Operation)

DTC Type Reference

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

Control Module References (Programming and Relearning) 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.
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.
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 (Symptom Related Diagnostic Procedures).

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

5. Command the cooling fans ON and OFF for LZ4-3.5L Gas, LZE, and LZG-3.9L Flex Fuel, or to 100 percent for LS4-5.3L. 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 (Cooling Fan Inoperative).

Circuit/System Testing

1. Test the thermostat for correct operation. Refer to Thermostat Diagnosis (Component Tests and General Diagnostics).
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 Cleaning and Inspection (Overhaul) for the 3.5L engine, Water Pump Cleaning and Inspection (Overhaul) for the 3.9L engine, or Water Pump Cleaning and Inspection (Overhaul) for the 5.3L engine.
4. Inspect the engine mechanical for worn/leaking/cracked cylinder heads or engine block. Refer to Coolant in Combustion Chamber (Coolant in Combustion Chamber) for the 3.5L engine, Coolant in Combustion Chamber (Coolant in Combustion Chamber) for the 3.9L engine, or Coolant in Combustion Chamber (Coolant in Combustion Chamber) for the 5.3L engine. Also refer to Coolant in Engine Oil (Coolant in Engine Oil) for the 3.5L engine, Coolant in Engine Oil (Coolant in Engine Oil) for the 3.9L engine, or the Coolant in Engine Oil (Coolant in Engine Oil) for the 5.3L engine.

Repair Instructions

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