Chevy & GMC Vans

I took my RV in for a smog test and the guy hooked up what appeared to be 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 the smog test guy should have hooked up to my OBDII port was the smog test machine

No, you have a lean code which isn't that uncommon. You'll want to check for vacuum leaks and fuel pressure first. Also, you need post your vehicle details with each question please.

I had no check engine light until he hooked up his computer my question is could he have done something to screw things up with a (scan tool with bidirectional controls) I might take it to another place maybe the Chevy dealer to check the ECM. In an article, I read the guy used his scan tool with bidirectional controls to program the purge valve to be closed could you program it to be open and give you these errors?

nope.
And bad ECM would also throw a code.

Like I said lean codes are very common. It's probably a rotten vacuum line.


2nd request: Please post your van info. Year + Model + Engine + odometer. Thank you.

2011 Chevrolet Express G3506.0L V8 SFI OHV 16V. 32,755 miles If I don't see a leak, I think it's possible a faulty purge valve from what I have read

here are the steps to diagnose your lean issue:
https://charm.li/Chevrolet/2011/Express ... rts/P0171/

Thanks for the input MountainManJoe

RobsRV wrote: ↑Mon Mar 31, 2025 11:08 am If I don't see a leak, I think it's possible a faulty purge valve from what I have read

A faulty purge valve also constitutes a vacuum leak. However, if this was the case, you would be getting EVAP trouble codes. (P0455, P0456, etc.)

Vacuum leaks can be elusive to spot. The best way to test for them is with a smoke machine.

Thanks, MoutainMan Joe you know your stuff
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

yeah cars don't like sitting that long. Especially with the crappy fuel we have these days. It goes bad so quickly. I would try running some fuel injector cleaner through it. Starting the engine and getting it hot once or twice a month will definitely help.

I have a smoke tester now, The question is, where is a good place to hook it up? I have seen a video where the guy hooked it on the brake booster vacuum line, but this van a 2011 Chevrolet Express G3506 has no vacuum-assisted brake booster. What a pain it was to get the engine cover off had to pull off some panels and take out the passenger seat. If somebody could point to a YouTube video, that would sure help. I'm having major hip pain right now so it's been a slow-going operation for me trying to get this fixed.
Maybe I can pull out the air filter assembly and rig something up to huck up the smoke tester

RobsRV wrote: ↑Fri Apr 04, 2025 10:23 pmwhere is a good place to hook it up?

any port on the intake. PCV/breather, HVAC, EVAP, EGR ...
component locations are in the service manual I posted earlier.