GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 2000 🢒 Montana Ext. 🢒 HVAC 🢒 Heating, Ventilation and Air Conditioning 🢒 Auxiliary Heater Core Replacement

Removal Procedure
  1. Drain the cooling system. Refer to Cooling System Draining and Filling in Engine Cooling.
  2. Raise and support vehicle. Refer to Lifting and Jacking the Vehicle in General Information.

    3. Object Number: 400657 Size: SH
  3. Disconnect the heater hose quick disconnects.
  4. Lower the vehicle.
  5. Remove the left side rear quarter lower trim panel. Refer to Rear Quarter Lower Trim Panel Replacement in Interior Trim.

    6. Object Number: 400641 Size: SH
  6. Remove the heater pipe bracket retaining screw.
  7. Remove the heater pipe bracket.
  8. Remove the heater pipe block fitting bolt.
  9. Carefully push the heater pipes downward to disconnect the heater pipe block fitting from the heater core.
  10. Remove the heater core retaining screws.

    11. Important: Carefully pull the heater core straight out from the HVAC module so not to damage the cooling fins of the heater core.


    Object Number: 400640 Size: SH
  11. Remove the heater core from the rear HVAC module.

Installation Procedure

    Important: Carefully insert the heater core straight into the HVAC module so not to damage the cooling fins of the heater core.


    Object Number: 400640 Size: SH
  1. Install the heater core to the rear HVAC module.

    2. 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.

  2. Install the heater core retaining screws

    3. Tighten
    Tighten the heater core retaining screws to 1.6 N·m (14 lb in).

  3. Carefully pull the heater pipes up and align the heater pipe block fitting to the heater core.

    4. Object Number: 400641 Size: SH
  4. Install the heater pipe block fitting retaining bolt.

    5. Tighten
    Tighten the heater pipe block fitting retaining bolt 16 N·m (12 lb ft).

  5. Install the heater pipe bracket.
  6. Install the heater pipe bracket retaining screw.

    7. Tighten
    Tighten the heater pipe bracket retaining screw 1.6 N·m (14 lb in).

  7. Install the left side rear quarter lower trim panel. Refer to Rear Quarter Lower Trim Panel Replacement in Interior Trim.
  8. Raise and support vehicle. Refer to Lifting and Jacking the Vehicle in General Information.

    9. Object Number: 400657 Size: SH
  9. Connect the heater hose quick disconnects
  10. Lower the vehicle
  11. Refill the cooling system. Refer to Cooling System Draining and Filling in Engine Cooling.