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 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 running.

• | DTC P0117 or P0118 are not set.

### Conditions for Setting the DTC

Coolant temperature more 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.

### 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

Control Module References for scan tool information

### Circuit/System Verification

Important: If DTC P1482 is set, diagnose that DTC 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--Refer to Symptoms - Engine Cooling.

### 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 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.