For 1990-2009 cars

### Diagnostic Instructions

• | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

• | Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• | Diagnostic Procedure Instructions provides 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 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.

### Conditions for Running the DTC

• | The engine is running.

• | DTC P0117, or P0118 are not set.

### 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

• | DTC P1258 is a Type A DTC.

• | The engine will operate in the Overheated Engine Protection Operating Mode.

• | The engine coolant indicator lamp will illuminate, 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 System Description and Operation

• | Instrument Cluster Description and Operation

• | Indicator/Warning Message Description and Operation

• | Audible Warnings Description and Operation

#### DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

#### Scan Tool Reference

• | Scan Tool Data List

• | Scan Tool Data Definitions

• | Scan Tool Output Controls

### 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, low and high speed. 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.
4. Inspect the engine mechanical for worn/leaking/cracked cylinder heads or 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.