For 1990-2009 cars

## DTC P1258 3.6L (LY7)

### Diagnostic Instructions

• | Perform Diagnostic System Check - Vehicle before proceeding with these diagnostic procedures.

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

• | Diagnostic Procedure Instructions provides an overview of each diagnostic category.

### DTC Descriptor

This diagnostic procedure supports the following DTC:

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 longer than the specified time. The ECM will disable half set of cylinders by turning OFF the fuel injectors. By disabling a half set of cylinders, the ECM is able to reduce the temperature of the coolant.

### Conditions for Running the DTC

• | The engine is running for more than 30 seconds

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

• | Once the above condition occurs and lasts for 1 second, P1258 runs continuously.

### Conditions for Setting the DTC

The ECM detects an ECT over 133°C (271°F) and lasts for 4 seconds.

### Action Taken When the DTC Sets

• | The ECM will illuminate the malfunction indicator lamp (MIL) during the first trip in which the diagnostic test has been run and failed.

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

• | Illuminate the coolant indicator lamp on the instrument panel (IP); the driver information center (if equipped) displays the data.

### Conditions for Clearing the DTC

• | The ECM will turn the MIL OFF after 3 consecutive trips that the diagnostic has been run and passed.

• | The history DTC will clear after forty consecutive warm-up cycles have occurred without a malfunction.

• | The DTC can be cleared by using the scan tool Clear DTC Information function.

### 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

#### Scan Tool Reference

• | Scan Tool Data List

• | Scan Tool Data Definitions

• | Scan Tool Output Controls

### Circuit/System Verification

Important: If DTC P0480 or P0481 are set, diagnose the above DTCs first.

1. Inspect the engine coolant level. The engine coolant level should be within the operating range. Refer to appropriate section in the Owner's Manual.
2. Ensure that the vehicle has the correct engine coolant with correct concentration. And the coolant should be fresh and contain additives. Refer to Recommended Fluids and Lubricants in Owner's Manual.
3. Check the coolant system below:

• | Cooling system leaks

• | Stuck or kinked cooling system hose, especially the radiator hose

• | To know if debris or other foreign material block the radiator and A/C condenser cooling fins.

Important: There is a short delay period before the ECM changes cooling fan speed.

4. Command that the two cooling fans operate at high and low speeds simultaneously.

⇒ | If both fans do not operate at the two speeds simultaneously--Refer to Cooling Fan Inoperative .

### Circuit/System Description

1. Check the thermostat for proper operation. Refer to Thermostat Diagnosis .
2. Test if the engine cooling system is overheating. Refer to Engine Overheating .
3. Inspect if the water pump and coolant flushing fluid operate correctly. Refer to Water Pump Replacement
4. Inspect the engine mechanical system for worn/leaking/cracked cylinder heads/blocked engine. Refer to Coolant in Combustion Chamber .

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

## DTC P1258 4.6L (LH2)

### 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

This diagnostic procedure supports the following DTC:

DTC P1258 Engine Coolant Overtemperature-Protection Mode Active

### Circuit 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. When an over temperature condition is present, DTC P1258 will set. The ECM will disable the half set of 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 runs

• | No ECT sensor DTCs set

### Conditions for Setting the DTC

• | The ECM detects an ECT over 131°C (267.8°F) for more than 2 seconds.

• | Once the engine protection mode is activated, DTC P1258 sets.

### Action Taken When the DTC Sets

• | DTC P1258 is a type A DTC

• | The engine will activate the Overheated Engine protection Operating Mode

• | Illuminate the coolant indicator lamp on the instrument panel (IP); the driver information center (if equipped) displays the data.

### 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

#### Scan Tool Reference

• | Scan Tool Data List

• | Scan Tool Data Definitions

• | Scan Tool Output Controls

### Circuit/System Verification

Important: If DTC P0480 or P0481 are set, diagnose the above DTCs first.

1. Inspect the engine coolant level. Engine coolant level should be within the operating range. Refer to Engine Cooling in Capacities -- Approximate Fluid in Owner's Manual.
2. Ensure that the vehicle has the correct engine coolant with correct concentration. And the coolant should be fresh and contain additives. Refer to Recommended Fluids and Lubricants in Owner's Manual.
3. Check the coolant system below:

• | Cooling system leaks

• | Stuck or kinked cooling system hose, especially the radiator hose

• | Loose, missing or damaged deflector

• | To know if debris or other foreign material block the radiator and A/C condenser cooling fins.

Important: There is a short delay period before the ECM changes cooling fan speed.

4. Command that the two cooling fans operate at high and low speeds simultaneously.

⇒ | If both fans do not operate at the two speeds simultaneously-Refer to Cooling Fan Inoperative .

### Circuit/System Description

1. Check the thermostat for proper operation. Refer to Thermostat Diagnosis .
2. Test if the engine cooling system is overheating. Refer to Engine Overheating .
3. Inspect if the water pump and coolant flushing fluid operate correctly. Refer to Water Pump Replacement .
4. Inspect the engine mechanical system for worn/leaking/cracked cylinder heads/blocked engine. Refer to Coolant in Combustion Chamber .

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.