This I have no idea, but I had the same issue. After changing the thermostat, still no heat. My issue ended up being the temperature control door actuator. If you remove the lower dash panels and glove box you can get to the screws holding it in. I did not have to remove the radio. Its the white box (aftermarkets are usually black)in front of the heater core area. Does your temperature (cold/hot) switch feel like it moves very freely? Mine did and apparently mine was stuck on cold. It cost $50 at advance auto parts and fixed my no heat issue after I changed the thermostat and ran water through the heater core to ensure it wasn't plugged.