One problem related to manifold/header/muffler/tail pipe has been reported for the 2015 GMC Terrain. The most recently reported issues are listed below. Please also check out the statistics and reliability analysis of the 2015 GMC Terrain based on all problems reported for the 2015 Terrain.
The manifold and the catalytic converter is cracked and emitting hazardous carbon monoxide inside the cabin of the car. For close to 2 months my husband has been driving the car like this and we have taken it to 2 mechanics and finally found the cracks. My husband has been getting sick from the carbon monoxide. It is a blessing he is still alive. According to online google searches this is a well known issue in this vehicle. The smell is strong especially when he uses the remote starter and when the car is in motion and stationary.