What could be the problem when a 1986 Cadillac Coupe DeVille doesn't pass smog because the check engine light doesn't light if the bulb is good and lights up but not when jumped for smog check?

Answer 1

I found this information at http://www.smogtips.com Contrary to public belief, the Check Engine light being illuminated anytime during the smog inspection is automatically a smog failure. Vehicle manufacturers have placed the Check Engine light inside the passenger compartment to inform the driver there has been or is an engine or drive train malfunction. Very often you may not notice an engine problem, but this is only because your engine's computer is operating under pre-programmed information rather then of real-time. In other words the problem still exists but your engine learns to live with it. To avoid spending hundreds down the road, the Check Engine light should be diagnosed as soon as possible by a reputable and certified auto repair station. Our recommendation is you have a certified smog repair shop conduct a full system diagnosis. Along with the "Check Engine" light being illuminated or not, there are stored computer codes in the engine contol computer which the smog station will be able to retrieve and use for diagnosing purposes. These codes more then often will direct the smog technian in finding the fault. For more information you may want to locate a reputable smog service center in your area by simply typing in your zip code in the Smog Shop Locator search section at www.smogtips.com