FredC7

My 5 year GMPP warranty on my 2008 C6 expired yesterday and the check engine light came on today. The check engine light came on last month while driving to Carlise. It went out after filling the gas tank on the return trip but it came back on later. I checked the 2 codes P0171/P0174 and they were for both banks running lean. I assumed that it was from driving long distances with the engine barely above idle. It seemed like it was lugging along in 6th gear climbing the hills in PA. I added some Tech cleaner to the tank and drove it about 120 miles before the check engine came back on today. I also blew out the air filter and the MAF but they were both pretty clean. I found my extended warranty paperwork but it expired yesterday. I will check the PCV valve and hose to see if it is stuck or has a hose leak. I hate to bring it to a dealer and would rather fix it myself. I will clean the MAF with some carb cleaner too.
Any suggestion on what else I should check next. I will have a friend read the codes tomorrow to see if they are the same two from last month. He had to replace a carbon filter sensor next to the gas tank on his 2008 but his threw a different code back then. I thought my problem might be dirty injectors from using Generic brand gas in PA but the cleaner should have fixed that. Plus I have used Sunoco 94 since then and have always used it.

taken19

Without the codes you are simply guessing. Post up what you find after pulling all locked in and pending codes so the forum can help out.

Joe_G

Those codes normally indicate a vacuum leak. Check for any air leaks between the maf and the engine. Have you ever had your intake manifold off?

If you clean your maf use maf cleaner. They are very sensitive and fragile. Some carb cleaners may not be good for it.

Keep us posted.

theVcar

Bumper to bumper traffic and CEL came on. I had Doug from ECS checkout out. Long short of it light went out on its own. Came on 2 woks later with code p0174 right bank lean. Cleared that at night, and in morning on again. Did a can of Sea Foam and drove it 75 miles and reset light. Will see if it comes on Saturday going to work. Ill drive it a little hard, but I'm afraid to go WOT if it is running Lean.
Thanks guys

FredC7

Thanks. I'll get MAF cleaner tomorrow but first I will check for air leaks. My engine bay has many stainless steel panels so it gets hot in heavy traffic. It may just be a bad vacuum hose. I have not had the intake off. This car is bone stock except for Borla exhaust. It has only 16K miles on it.

EVRose

It went off after you got gas but came back on. I would check the seal on the gas cap.

Joe_G

Check the hose from the valley cover to the intake and the brake booster hose. I'd be surprised if it was them, they seldom have problems. Those are the only vacuum lines unless you have npp. The heat in your engine compartment shouldn't be a problem. I am wondering if your maf is loose in the bridge or if the bridge is loose from the accordion. Check that path first.

Shouldn't be your gas cap, that sets a different code and it will say "check gas cap" on the DIC.

I also can't imagine it's the gas you put in unless you put in e85 or e30 by mistake.

FredC7

Your problem is exactly like mine on my 2008. Let me know if you get it fixed. I checked hoses this morning and can not find an obvious air leak. Next is to clean the MAF and reset the codes.

truckplay

it sounds like a vac. leak. did you work on the car ?
clean the mass CAREFULLY and check all your clamps.

FredC7

Today I pulled the FRCs to check again for a vacuum leaks but nothing was obvious. All of the hoses appear intact and I could not hear any sucking air sounds. I did check the codes and they were the same as before, P0171 and P0174, for running lean both banks.
I called Paul Masse Chevrolet Service Dept in RI as they were recommended by other club members. My car has never been to a dealer for service. I do all my own oil changes on my 4-post lift. I explained that it threw the codes back in August but I had reset them. I drove over 200 miles before they came back on and I learned that my extended GMPP warranty expired 2 days ago. He said that once it has expired there is nothing they can do under the warranty. After explaining the problem he suggested that I make sure that the oil cap is on very tight because they have had other Corvettes with the same lean run codes and it turned out to be a bad seal on the oil filler cap. I have an after-market billet aluminum oil cap that has been on the car for 4 years. I put back the OEM cap and reset the codes. I'll take it on a long drive later to see if the codes come back. If they do I will have to bite the bullet and take it in to the dealer.
Has anyone ever heard of a bad oil filler cap causing run lean codes. I hope this guy it not blowing smoke up my rear.

Joe_G

No oil cap or bad one could do it as you are adding unmetered air into the intake via the valley port to the intake.

theVcar

Mine came back on. I don't see any loose or disconnect hoses. Ill pet a screwdriver to the coupling fro my CAI to MAF

1fastbob

Improperly installed oil fill cap caused all kinds of weird idle issues and check engine light on my 2006 BMW Z4. It is certainly worth checking.

theVcar

I also had surging in 1/2/3 gear if to slow. I have a ported fast 102 and I checked all the hex nuts. Most WERE a little loose. From a 1/16 to a full 1/4 and then some.

Joe_G

I should have asked about your mods in the first post.

If you have a fast 102 it could be as simple as the car needing to be tuned. Take it to your tuner and have them scan the car and make adjustments to your maf as needed.

theVcar

The car has a great tune ever since the 102 was put on. Never an issue, Doug does a great job in So Jersey.
I'm going fishing with 3 old timers down in Warestown. A long drive, I hope light doesn't come on. I think I fixed it with making those screws snug.

FredC7

Well I did as the Chevy Service department suggested. I put back the OEM oil cap and made sure it was tight. I reset the CEL and it came back on very soon. Next I cleaned the MAF with electronics spray but CEL light stayed on. Then I filled the tank with top tier Shell gas and on the 2nd starting cycle the light went out. I drove it about 100 miles before the light came back on so it looks like the car will have to make a trip to the dealer for that dreaded service. I don't want to drive it much just in case it is actually running lean and not just a sensor error.
If this dealer is like most dealer service they will just keep replacing parts until they hit upon the fix.

EVRose

I know the codes say otherwise but it still sounds to me like a bad seal on the gas cap since the light comes and goes when you fill up. I've seen many threads about a bad cap setting off the CEL and not the Check Gas Gap warning and I think there was even a TSB about it. Replacing it is a cheap thing to just try before you let the dealer start messing with it.

FredC7

I will give it a try. I happen to have a spare gas cap for a C6 from a friend that went through several parts before determining that it was a sensor next to the gas that was causing his CEL, but with different codes than mine.