My mom has an 88 V6 4runner. Normally when you start it, all the warning lights (brakes, check engine etc) come on and then go off. She says lately they have all been staying on longer an longer, and stayed on for about 15 minutes the other day before going off. She's worried it's going to quit. She had a shop check the codes, there are none. They are clueless. Any ideas what would cause this?