GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2003 🢒 Monte Carlo 🢒 Engine 🢒 Engine Cooling 🢒 Heater Core Replacement

Tools Required

J 38185 Hose Clamp Pliers

Removal Procedure
  1. Remove the fuel injector sight shield, if equipped with 3.8L. Refer to Fuel Injector Sight Shield Replacement in Engine Mechanical-3.8L.
  2. Drain the coolant. Refer to Cooling System Draining and Filling in Engine Cooling.

    3. Object Number: 415886 Size: SH
  3. UseJ 38185 in order to position aside the heater hose inlet and outlet clamp at the heater core.
  4. Disconnect the inlet and outlet heater hose from the heater core.
  5. Remove the vacuum tank. Refer to Vacuum Tank Replacement in HVAC System - Manual.
  6. Remove the floor carpet. Refer to Front Floor Panel Carpet Replacement in Interior Trim.
  7. Remove the rear floor air outlet duct from the holes in the floor reinforcement.
  8. Disconnect the rear floor air outlet duct from the heater core outlet cover.
  9. Remove the bolts from the vaccum harness bracket and position bracket aside.

    10. Object Number: 508311 Size: SH

    Important: Position the heater outlet cover downward and rearward in order to disconnect the cover from the rear area floor duct assembly.

  10. Remove the heater outlet cover screws.
  11. Remove the heater outlet cover.

    12. Object Number: 295349 Size: SH
  12. Remove the heater core cover screws.
  13. Remove the heater core cover.

    14. Object Number: 143978 Size: SH
  14. Remove and discard the seals (1,2) from the heater core cover.
  15. Remove the caulk (3) from the heater core outlet cover.

    16. Object Number: 296242 Size: SH
  16. Remove and discard the outer seal  (5) from the heater core.

    17. Object Number: 295351 Size: SH
  17. Remove the heater core pipe retainer clamp screw (2) from the heater core retainer clamp.
  18. Remove the heater core retaining clamp screw (1) from the heater core.
  19. Remove the retaining clamp from the heater core.

    20. Object Number: 295353 Size: SH
  20. Remove the heater core from the HVAC lower case.
  21. Remove the heater core pipe retainer clamp from the heater core pipes.

    22. Object Number: 143987 Size: SH
  22. Remove and discard the heater core lower seal (4) from the HVAC case.

    23. Object Number: 143992 Size: SH
  23. Remove and discard the heater core center seal (3) from the HVAC case.

    24. Object Number: 143985 Size: SH
  24. Remove and discard the heater core upper seal (2) from the HVAC lower case.

    25. Object Number: 143990 Size: SH
  25. Remove and discard the heater core side seals (1) from the HVAC lower case.

Installation Procedure

    Object Number: 143990 Size: SH
  1. Install new heater core side seals (1) to the HVAC lower case.

    2. Object Number: 143985 Size: SH
  2. Install a new heater core upper seal (2) to the HVAC lower case.

    3. Object Number: 143992 Size: SH
  3. Install a new heater core center seal (3) to the HVAC case.

    4. Object Number: 143987 Size: SH
  4. Install a new heater core lower seal  (4) to the HVAC case.

    5. Object Number: 295353 Size: SH
  5. Install the heater core retaining clamp to the heater core pipes.
  6. Install the heater core in to the HVAC lower case.

    7. Object Number: 295351 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.

  7. Install the screw (2) to the heater core retaining clamp.

    8. Tighten
    Tighten the clamp screw to 1.5 N·m (13 lb in).

  8. Install the heater core mounting clip with a screw (1).

    9. Tighten
    Tighten the screw to 1.5 N·m (13 lb in).


    Object Number: 296242 Size: SH
  9. Install heater core outer seal (5) to the heater core.

    10. Object Number: 143978 Size: SH
  10. Install new seals (1,2) to the heater core cover.
  11. Install the caulk (3) on to the heater core outlet cover.

    12. Object Number: 295349 Size: SH
  12. Install the heater core cover.
  13. Install the heater core cover screws.

    14. Tighten
    Tighten the cover screws to 1.5 N·m (13 lb in).


    Object Number: 508311 Size: SH
  14. Install the heater core outlet cover.
  15. Install the screws to the heater core outlet cover.

    16. Tighten
    Tighten the screws to 1.5 N·m (13 lb in).

  16. Install the HVAC vaccum harness bracket .
  17. Install the screws to the HVAC vaccum harness bracket.

    18. Tighten
    Tighten the screws to 1.5 N·m (13 lb in).

  18. Connect the rear floor air outlet duct to the heater core outlet cover.
  19. Install the rear floor air outlet duct to the holes in the floor reinforcement.
  20. Install the floor carpet. Refer to Front Floor Panel Carpet Replacement in Interior Trim.
  21. Install the vacuum tank. Refer to Vacuum Tank Replacement in HVAC System - Manual.

    22. Object Number: 415886 Size: SH
  22. Connect the inlet and outlet heater hose to the heater core.

    23. Important: Reposition the heater core hose clamps in the indicated location.

  23. UseJ 38185 in order to reposition the heater hose inlet and outlet clamp to the heater core.
  24. Refill the coolant. Refer to Cooling System Draining and Filling in Engine Cooling.
  25. Install the fuel injector sight shield, if equipped with 3.8L. Refer to Fuel Injector Sight Shield Replacement in Engine Mechanical-3.8L.