99chevy612

My service engine soon light used to come and go its self so I let it go. Now it stays on so I hooked my code scanner to it and it read system to lean in bank 1 and 2. I took off the mass air flow sensor and cleaned it. I did my own little smoke test with a cigar, no vacuum leaks. Changed the pcv valve. The code reader tells me that my 02 sensor are in good condition. My fuel pump and fuel filter were replaced 16k miles ago. Truck runs fine, no hesitation or anything. Just bugs me that the light is on. OBD codes alsot says it could be an exhaust leak between the 02 sensor and the engine but my exhaust manifold and gasket was replaced 16k miles ago when I bought the truck. I'm running out of things it could be. Please help! Thanks

cleveland63b

you need a full function scanner or actual smoke machine to test for vacuum leaks. The "cigar test" is a joke the only way I see that working is if you can puff like crazy and the leak is huge.


More than likely your intake manifold gaskets are leaking but you need to test to be sure.

99chevy612

Well I actually used my vape that has a lot of smoke but I didn't know if everyone knew what that is. But anyway the light went off. It may have went off from me cleaning the MAS or changing the pcv valve yesterday and my computer only did a new test now and seen that the problem is corrected. Or it may just be going off and may come back on like it used to. But I don't see how a exhaust manifold leak can cause that light to come on. I know a lot of people that have much worse exhaust leaks than me and they don't have the light.

cleveland63b

intake manifold not exhaust - if the intake gasket is leaking it will pull in unmetered air...basically causing the maf readings to disagree with 02 readings


Intake gaskets are a very common problem and anytime you get a lean code for both banks its the very first thing I check, then I move on to fuel pressure from there. Get a scanner that can read fuel trims and post what they read at idle and around 2000rpm

99chevy612

Okay I'll do that when I get the chance. Now that the light went off, I plugged my scanner in just to see if it still reads codes. The light is off and now it only reason po171. System to lean in bank 1.