Doesn't anyone want to know what code(s) caused the light to come on? NeilC doesn't have a starting or running complaint does he? How about checking the vacuum supply line to the EGR and Air injection switchover valves? I've seen the line cracked (usually behind the black plastic front cover) dozens of times. That type of vacuum tubing becomes very brittle with age and it needs to be moved out of the way during a head gasket job. By the way, I'm not disagreeing with you guys about the possibility of "discovering a failure"(I like that term) such as a 104 harness, while performing other work. It's just that in my experience I'd look real close at that vacuum line. So Neil, what code lit the lamp?