When I started my truck up after work tonight I noticed the SES light come on and stay on. Now I did not notice anything out of the ordinary with the way the truck was running, no loss of power, all gauges were reading properly. I do have the o2 simulator, I was wondering if other people with the sim noticed an SES light in either the cold weather or wet weather? We just had a big snow storm over the weekend, I was thinking that the simulator could have gotten wet somehow and maybe this would cause the SES to come on. I haven't been able to look at it because it is dark outside, but I will check the sim out tomorrow. I will have access to a scan tool this weekend but was curious if anyone else had noticed anything like this.