If the check engine light is on and it is not storing any DTC's there is 2 probable causes. The keep alive memory fuse or circut is no good. check fuse f2.36 in the CJB. Also check to see if you have power all the time on pin 55 at the pcm. If the KAM fuse and circuts are good you probably have a bad PCM. The pcm should store a code anytime the MIL is on. If it doesn't there is an issue with the keep alive power or an internal pcm issue.