- 1). Open the hood of the GMC truck and disconnect the negative terminal cable from the battery with a socket wrench.
- 2). Pull up on the coolant reservoir tank on the right-hand side of the engine compartment to remove it. Place a drain pan under the radiator and loosen the radiator drain plug underneath the vehicle to allow all of the coolant to drain.
- 3). Disconnect the heater hoses from the radiator. Remove the bolts from the heater case to the firewall at the rear of the engine compartment with a socket wrench.
- 4). Remove the glove box by uninstalling its securing bolt and pulling it off the dashboard. Disconnect the electronic control module's electrical connector next to the glove box and remove it from the vehicle.
- 5). Remove the two bolts securing the right-side kick panel. Remove the three heater case mounting bolts. This will allow access to the heater core itself.
- 6). Pull the old heater core out of the truck. Place the new heater core into the truck and securing it by installing the heater case mounting bolts.
- 7). Reattach the right-side kick panel. Reconnect the electronic control module and place it back into the vehicle. Reattach the glove box and reconnect the screws from the heater case to the firewall.
- 8). Reattach the heater hoses to the radiator. Tighten the radiator drain plug and pour new coolant into the radiator until it reaches the "Max" line. Place the coolant reservoir tank back into the engine compartment and reconnect the battery. Close the hood.
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