How to Replace the Heater Core in a 1995 GMC Sonoma

The heater core in your 1995 GMC Sonoma truck heats the engine coolant to make the heater work. If the heater core has gone bad, you need to replace it, and this is not an easy task. On older models like the 1995 Sonoma, you don't have to completely remove the heating/ventilation module from the truck to replace the heater core. But you will still need to remove the dashboard in order to reach the module and replace the heater core.

Instructions

Accessing the Module

1

Loosen the truck battery's negative cable clamp nut with a wrench and disconnect the cable.

2

Place a large container underneath the radiator at its drain plug. Remove the plug and drain the engine coolant into the container. Drain any remaining coolant at the engine block drain plug.

3

Disconnect the two heater core tubes from within the engine compartment at the firewall and plug the open fittings.

4

Detach the lower dash panels, removing the screws with a screwdriver and detaching the two clips on each panel.

5

Unscrew the radio's two mounting fasteners with a small wrench. Remove the radio from the dash. Unplug the radio's electrical connector and the antenna cable lead.

6

Remove the bolt that is at each end of the pivot bracket with your wrench. Remove the two Torx screws near the brackets with a Torx wrench. Remove the one bolt near the center bottom of the dash, which is on the steel pencil brace.

7

Remove the steering column's four mounting nuts and lower the steering column.

8

Pry the defroster grill and the speaker grilles from the dash panel using a flat-head screwdriver. Remove the dash panel bolts located in the now-opened holes using your wrench.

9

Remove all remaining bolts for the dash and pivot it to the rear, then disconnect all wiring connectors behind the panel. Pull the dash out and remove it from the vehicle; you may need a second person's help.

Replacing the Heater Core

10

Unbolt and remove the pencil brace on the heating unit's heater core cover with your wrench. Remove the screws holding the cover, the straps and the bracket that covers the tubes with your screwdriver. Pull out the core without bending the tubes.

11

Install the new core in the heating/ventilation unit and screw the bracket and straps in place. Screw the cover in place and bolt the pencil brace back on.

12

Place the dashboard back on the pivots. Reconnect all the electrical connectors on the dash. Pivot the dash into position and reconnect all the fasteners with your wrenches and screwdriver.

13

Raise the steering wheel back into position and secure it with its mounting nuts and your wrench.

14

Mount the radio back into the dashboard. Connect the wiring and the antenna. Secure the radio to the dash with the two fasteners.

15

Reconnect the bolts and the Torx screws to the pivot bracket with your wrenches. Clip and screw the lower dash panels in place.

16

Pour the engine coolant back in the radiator at its fill neck. If the coolant is dirty or otherwise contaminated, use a fresh mixture of water and antifreeze.

17

Reconnect the Sonoma's battery cable.