Just as the title says. I'm sure the question has been asked before, but I couldn't find anything through the search feature. The issue is that sometimes the torque converter in my car locks up perfectly and functions just fine, then other times it doesn't lock up at all. Pulling up on the brake pedal doesn't have any effect. The transmission shifts perfectly otherwise. What could be the issue here? A failed sensor somewhere? I'm not sure.
It's a 1995 Grand Prix 4T60E