I took my RV in for a smog and the guy hooked up a (scan tool with bidirectional controls), and lo and behold, I have a check engine light I didn't have before. Is it possible for someone to use a bidirectional scan tool to for example, set your purge valve open or change other settings to cause the check engine light to come on and give you P0171 & P0174 codes? Seems to me the only thing that should have been hooked up to my OBDII port was the smog test machine

 

More to the story, I hadn't driven the van, which happens to be an RV, for 5 months, and the battery was dead and unrecoverable. I replaced it and drove the RV for about 30 miles with no check engine light. Then when I took it in for smog, the guy said you're running lean I said but I have no check engine light he says you will and lo and behold, right before my eyes, the check engine light comes on. He had his own computer, which I assume to be a (scan tool with bidirectional controls). so maybe you can see how I might assume he did something. I guess next time I take a vehicle in for smog I should use my symple scan tool and check for errors and run a test. I probably should drive that RV 5 of 10 miles once a month, too
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It may have had a pending code that a scan tool would see before it threw a CEL.

 

That's probably what happened in this case

 

I did have a cracked vacuum tube