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Hello all and happy holidays!

'13 LTZ 81k

For those who have been following my issue you know I've been having high long term fuel trims, mostly on bank 2 but bank 1 is acting up almost as bad now.

Well I finally took it to the dealer after having it smoke tested for vacuum leaks by a local shop. Needless to say I was underwhelmed with the dealers awnser. I was told basically if there's no check engine light there's nothing they can do, which I kinda get, it does make tracking down a problem harder. But that's why they charge so much is to find the hard stuff. I was also told as engines age they get more out of tune and that's why fuel trim exists, to keep the engine in 14.7:1 (yes I agree). But I was surprised when he (service advisor) said "+20% or higher is fine as long as it doesn't stay there". That's when I called BS! I was also told that at normal operating temperatures it's normal when stopped at a red light (for example) for the car to go back into open loop and into another mixture other than 14.7:1... I could see this if it was still cold or something was wrong, but not under normal conditions.

When I was told the car was done I was unable to pick it up until the next morning, so it cold soaked. When I drove off, I got a "tighten gas cap" message, which a stopped and did. When I got home I scanned everything and found a P0445 evap leak (no surprise) so I now have a new vent canaster solenoid, the one by the filler neck, I've already replaced the evap solenoid because it couldn't hold a vacuum. We shall see after I install it if it makes a difference.

The new mystery is a U0140 code (lost communication with BCM) I did some reasarch and found it's related to fuel/air metering in the BCM. And also it's not listed in alldata as a code that (I'm assuming) applies to my car because I can't find it, so why did the scanner pick it up? The repair slip from the dealer says "all codes cleared" so it had to of picked it up on the 20 minute drive home. It's interesting it's directly related to fuel/air metering, which I didn't know the BCM had anything to do with???

Any thoughts would be appreciated!
 

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That has to be hard to deal with for sure. I am sorry your having issues even with taking it into the dealer for repair...

Wondering if your scan tool lets you set up some monitoring tools for testing? Also sadly there is ways of working on a car with history of problems without a code set. Sadly just needs to be set up to test over things. This could be Saved history or live data but can be done in Theory.

Now I will get laughed out of the room here and that is fine. But One of the things that is hard to find in an issue with Cars with Trim related issues could be Wait for it lol... An Exhaust Leak. Problem with that say being before the 02 is that when the data is read by the 02 it will think the issue is within the motor not knowing it is coming from a leak. So it thinks it is coming from the motor and sends data to send more fuel, thinking it is lean. However because it was really a NO issue motor everything is working well it would make the car run rich.

I am not sure if the shop only did a Smoke test on the Motor side or if it was also part of the Exhaust side but seems that always gets looked over and problem sticks around while people toss parts at the car.

Hope you get it worked out soon
James
 
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