Bought the car in January of 2026. It is a 1 owner vehicle with 115.000 miles on the clock. My wife loved the car. And it was priced below the current value (according to the dealer) My wife used this as her primary vehicle for her job as a real estate agent. At first she wasn’t putting a lot of miles on it but when the spring came she was more active. Everything was fine with the car until August. The first problem came as a check engine light for bank 1 oxygen sensor. No biggie, changed the sensor. Everything was fine for about 2 weeks. Then the check engine light came back on. This time code P0301; misfire detected in cylinder 1. Again no biggie, changed all 4 plugs & coils with GM AC Delco parts. The code never went away. Sent the car to Cadillac dealer and explained what was happening. Was charged $200 for them doing everything I already did (checking coils & plugs, swapping into different cylinders, etc.) They wanted to charge me $600 to do further testing to which I declined because I was under the impression that the initial diagnostic test I was paying for was the testing beyond what I had already done.

After consulting online resources it was suggested that it could be a faulty fuel injector. I wasn’t set up to test an injector so I took it to a shop that specializes in such. They contacted me a few hours later after dropping the car off to say they couldn’t do it due to how bad the misfire was. Let be back up a bit and describe what the car was acutely doing. Upon starting the car rattled and popped like the engine wanted to stall. Once moving the car was normal at highway speeds but once it got off the highway back to the rattles & pops. Also the check engine light would come back on as well as a “Service Stabilitrack” & “AWD Off” message. So then the car was taken to another GM dealer and again it was explained what was occurring. Believing that they knew where exactly what the culprit was I was shocked to find out they did the exact same thing the other dealership did, and charging me $190 for their initial diagnostic test (which wasn’t much) and then quoting me a labor only price of $1500 to tear into the engine to see what the internals were doing. Of course I refused because they didn’t have an exact direction of what it could be and in my mind $1500 just to take the top of the engine block off just to look at what was going on was outrageous. So after retrieving the car from the dealership It began a new trick on the 15min ride home. Now the engine makes no boost from the turbo, reduced engine power message, and the car started overheating. So let’s do the math:

*Changing out coils & plugs : $200 (parts only, did the work myself)

*First dealership diagnostic : $200 with no answers or possible reasons

*Second dealership diagnostic: $190 with no answers or fix

So that’s $590 invested with no answer as to what is causing my issue. Sourced a replacement engine online, rebuilt of course, for about $1300. Got a quote from one shop of about $2000 to install. At this point this seems like the only option to get the car back on the road.