My '09 LaCrosse started having an issue about three weeks ago. Nothing major, just sputtering under light load once warmed up - like a coil pack or bad plug. I waited around waiting for a CEL even checking a couple of times for codes with my Actron scanner even though I didn't have a CEL. No codes found every time. So I take it to the dealer and they found a misfire code on one cylinder. Why would the Actron, which I've used for a few years to pull codes off a few vehicles, not pick up a misfire condition where the GM tool was able to pick it up? I don't get it - either the code is there or it's not, and I know the Actron can report misfire codes. Are there different misfire codes beyond just identifying the cylinder?

 

Not all codes trip the CEL and your scanner probably only reads the CEL light codes, not the smaller ones stored in the PCM that are pulled during diagnostic test computers

 

+1. Most of those cheap code readers (read, not scan tool), only show MIL codes, nothing else.

 

Thanks for the input on the PCM, I didn't realize the codes could be stored in different places. For the record though, this isn't one of the entry level scanners - it's an Actron CP9175. Not a professional level device by any means, but I'd expect it to find a reported misfire condition.

 

Yeah, that's weird. I have a cheapest-of-the-cheap ELM 327 that is able to read 'pending' codes. Could the connection be 'off' somehow? Are you still able to read other parameters with your Actron?