I've tried checking codes in the past. Never was able to comprehend exactly how to determine the CEL. Another problem has arisen now to top it off. I changed my schedule reccently starting next week I'll have more time to mess with it. Still don't know what I'm doing and Im pretty sure the CEL doesn't have to do with this problem. I forgot to mention it's been on since I bought it. Sometimes it doesn't come on at all.