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 the 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-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 for greater than 30 seconds.

• | DTC P0116, P0117, P0118, or P0128 are not set.

### Conditions for Setting the DTC

The ECM detects that engine coolant temperature is greater than 136°C (277°F) for more than 1 second or a cumulative time of 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 instrument panel (IP) will illuminate the coolant 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 System 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

Note: If DTCs P0480, P0481, P0691, P0692, P0693, or P0694 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:

• | Cooling system 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.

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

4. Command the cooling fans in both low and high speed.

⇒ | If the cooling fans do not operate in both speeds, refer to Cooling Fan Inoperative.

5. Test the thermostat for correct operation. Refer to Thermostat Diagnosis.
6. Test the engine cooling system for overheating. Refer to Engine Overheating.
7. Inspect the water pump and coolant flow for correct operation. Refer to Water Pump Replacement.
8. Inspect the engine mechanical 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.