I took my 2011 Silverado Z71 to a Chevy dealership for a P0011 timing issue. They said the timing chain had stretched and needed to be replaced. I have a 3rd party extended warranty, they agreed to cover the repair and the dealership did the work. I picked up the truck and the check engine light came on right after I left their lot. I took it back and they said now the camshaft phasers need to be replaced. The warranty company approved this work and the dealership replaced them. They called me up and said the work was done but they're still having the same CEL code. After going back and forth between them and the warranty company they did a tear down and found that a check ball had broken off of the end of the camshaft and scored it.
The fix now they say is to replace the camshaft and lifters. The warranty company agreed to cover this repair but said they camshaft phaser repair was a misdiagnosis and that they expected the dealership to eat the labor and any duplicated parts. The dealer's position is that the phasers were bad and that it was a valid repair. They insist that they followed the proper GM troubleshooting and repair procedures and they are not willing to eat any repair costs.
At this point my truck is sitting at their lot with the engine stripped down to the block. The dealer wants around $5000 to complete the repairs, this is on top of $4k+ the warranty has authorized and in addition to the combined $2500 the warranty company and I paid for the original timing chain repair issue. My question is does it sound like the dealership did a proper diagnosis? The warranty company said they should have noticed the damage to the cam when the phasers were replaced but the dealership said they didn't tear down far enough to see that damage as there was no reason to.
My other question is how do I know for sure this will actually resolve the issue? I don't want to drop all this money into it just to find out there is some other issue. Is there anything else I should have them look at or do will it's down to this point?