GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Generic 🢒 2008 🢒 Unit Repair 🢒 Engine 🢒 Engine Controls and Fuel - LS Engines 🢒 DTC P1258

Diagnostic Instructions
    • Perform the Powertrain On Board Diagnostic (OBD) System Check 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
    • DTC P0117 or P0118 are not set
    • The engine is running

Conditions for Setting the DTC

The ECM detects the coolant temperature is greater 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.

Conditions for Clearing the DTC

DTC P1258 is a Type A DTC.

Diagnostic Aids
    • After starting the engine, the ECT sensor temperature should rise steadily, then stabilize after the thermostat opens.
    • If the vehicle has set overnight, the ECT sensor and the IAT sensor values should display within 3°C (5°F).
    • Test the ECT sensor at various temperature levels in order to evaluate the possibility of a skewed sensor. A skewed sensor can result in a driveability condition.

Reference Information

Schematic Reference

Engine Controls Schematics

Connector End View Reference

    •  Engine Control Module Connector End Views
    •  Engine Controls Connector End Views

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

DTC Type Reference

Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Engine Control Module Scan Tool Information

Circuit/System Verification
  1. Engine operating, observe the scan tool ECT parameter. The ECT should be less than 132°C (270°F).
  2. Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

Circuit/System Testing
  1. Inspect the cooling system for the following:
    2. • Coolant system for leaks and at the proper level
    • Verify the accessory belt is installed correctly.
    • Kinked or pinched radiator hoses
    • Verify the thermostat is operating correctly.
    • Verify the water pump is operating correctly.
    • The radiator and A/C condenser for any air flow obstructions.
    • Inspect the engine for worn/leaking/cracked cylinder heads and engine block.
    ⇒If a condition is located, repair as necessary.
  2. Command the cooling fan speed from 0% to 100% with a scan tool. Verify proper cooling fan operation.
    3. ⇒If the cooling fan does not respond to the commanded states, refer to Cooling Fan Inoperative .

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.