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 the cylinders, the ECM is able to reduce the temperature of the coolant.

Coolant temperature more than 130°C (266°F) for more than 10 seconds.

DTC P1258 is a Type A DTC.

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

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:

•

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.

1. Test the thermostat for correct operation.
2. Test the fan clutch for proper operation.
3. Test the engine cooling system for overheating.
4. Inspect the water pump and coolant flow for correct operation. Refer to Water Pump Cleaning and Inspection.
5. Inspect the engine for worn/leaking/cracked cylinder heads and engine block. Refer to Coolant in Combustion Chamber and Coolant in Engine Oil.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.