GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 1998 🢒 DeVille 🢒 Engine 🢒 Engine Cooling 🢒 Heater Core Replacement

Removal Procedure

    Caution: Unless directed otherwise, the ignition and start switch must be in the OFF or LOCK position, and all electrical loads must be OFF before servicing any electrical component. Disconnect the negative battery cable to prevent an electrical spark should a tool or equipment come in contact with an exposed electrical terminal. Failure to follow these precautions may result in personal injury and/or damage to the vehicle or its components.

  1. Disconnect the negative battery cable.
  2. Partially drain the coolant. Refer to Cooling System Draining and Filling in Engine Cooling.
  3. Remove the instrument panel compartment. Refer to Instrument Panel Storage Compartment Replacement in Instrument Panel, Gauges and Console.
  4. Remove the right sound insulator. Refer to Instrument Panel Insulator Panel Replacement - Right Side in Instrument Panel, Gauges and Console.
  5. Remove the heater and A/C programmer. Refer to Programmer Replacement .
  6. Disconnect the driver air mix actuator (2).
  7. Disconnect the passenger air mix actuator (3).

    8. Object Number: 305037 Size: SH
  8. Remove the heater core cover.

    9. Object Number: 378606 Size: SH
  9. Remove the inlet and outlet heater hoses from the heater core.

    10. Object Number: 381380 Size: SH
  10. Remove the heater retaining screws.
  11. Remove the heater core.

Installation Procedure

    Object Number: 381380 Size: SH

    Notice: Use the correct fastener in the correct location. Replacement fasteners must be the correct part number for that application. Fasteners requiring replacement or fasteners requiring the use of thread locking compound or sealant are identified in the service procedure. Do not use paints, lubricants, or corrosion inhibitors on fasteners or fastener joint surfaces unless specified. These coatings affect fastener torque and joint clamping force and may damage the fastener. Use the correct tightening sequence and specifications when installing fasteners in order to avoid damage to parts and systems.

  1. Install the heater core to the heater case using the 2 screws.

    2. Tighten
    Tighten the screws to 2 N·m (18 lb in).


    Object Number: 378606 Size: SH
  2. Install the inlet and outlet heater hoses to the heater core.

    3. Object Number: 305037 Size: SH
  3. Install the heater core cover and the screws.

    4. Tighten
    Tighten the screws to 2 N·m (18 lb in).

  4. Connect the passenger air mix actuator (3).
  5. Connect the driver air mix actuator (2).
  6. Install the heater and A/C programmer. Refer to Programmer Replacement .
  7. Install the instrument panel compartment. Refer to Instrument Panel Storage Compartment Replacement in Instrument Panel, Gauges and Console.
  8. Install the right sound insulator. Refer to Instrument Panel Insulator Panel Replacement - Right Side in Instrument Panel, Gauges and Console.
  9. Connect the negative battery cable.
  10. Refill the cooling system. Refer to Cooling System Draining and Filling in Engine Cooling.
  11. Adjust the air mix valve. Refer to Temperature Valve Link Adjustment - Driver and to Temperature Valve Replacement - Passenger .