The car has about 120000 on it, I'm not sure if the timing chain is original or if it has been replaced as I'm not the original owner.
Absent documentation, you can be sure the previous owner hasn't replaced anything. While I'm not suggesting you don't consider all possibilities, the likely answer to a timing chain code is . . . worn timing chains. At 120K miles you're due for some maintenance, as you would be for any make of car with that mileage. Fortunately the CTS is a worthwhile car. Likely you'll need timing chains, water pump, shocks, control arms, motor mounts, alternator and eventually a driveshaft. Not necessarily in that order.