Manager Forum

Where can I find information on the diagnostic trouble codes that turn on the CEL or do not turn on the CEL? In doing emissions inspections and work that would be useful information at times.

there are hard codes and pending codes. Some take three cycles of failures to turn on light and if this is an emission related fault while in pending it will pass most states emission inspections. There are times when we get a vehicle that failed emission testing with no lite on and we have to seek out the pending fault. Newer scanners make this fairly simple since they offer hard or pending right in the same window. My older scanner don't and they take up a lot of time searching one by one. As far as a direct answer to you question is, in my opinion any code that will set and not turn on the light is in readiness to do so. It just is waiting for the rest of the necessary information. I can't say how long a pending code will sit in readiness and haven't seen any description or time frame in my readings. I just know if it's there I will not clear it unless the trigger time is over 30 days.

People who clear codes to see what will happen need to understand it will make the repair time (mostly) longer and more expensive. It drives me up a wall when I find out the light has been turned off over and over again by the customer and they expect you to formulate an answer with all the useless information they provide. Many get disgusted and angry because they did most of the investigating and just want the quick fix information from me. No one seems to see the underlying issues such as a small vacuum leak causing a lean code, they want a price to install an aftermarket, used, universal OX sensor because that what Bucky and Bill Bob said it was between beers.