The truck check engine lights came on, and I took it to a dealer. I was told the ECM was faulty, they replaced it, but it didn’t fix the issue. I was then told the ONSTAR telematics unit was faulty. The truck has been down for 45 days, with no ETA on parts(several forms say 4-6 months). There is no guarantee that this will fix the CEL. The truck is inoperable at this time.