Are you saying the check engine light is still on?
Usually if the CEL is flashing that means there is a problem that needs to be addressed immediately. If the CEL is simply on steady, thereās a problem that needs to be addressed with due speed, but thereās no engine-damaging emergency happening. Thereās various P codes for possible faults in O2 sensors. The one for the cat is usually P0420, which indicates thereās a problem in the measurements comparing a pre-cat o2 sensor to a corresponding post-cat o2 sensor. A search of this forum will show that posters here drive with P0420 presumably without the serious engine damaging problem you experienced. Iāve never heard here of a shop doing a pro-active compression test for a P0420. If thatās a known problem unique to your make/model/year etc then you might have a valid argument they should have done a compression test. But it seems a sort of hypothetical argument, not based on a fact that did happen, but something that might happenā¦
I donāt know what your mechanics notes show, I am going off of what was reported on the repair order that you posted.
āInitially faulty ECU had stored codes for 02 sensor failure. New ECU is picking up codes for cat converter and knock sensor failure.ā
If they knew the catalytic converter failed and damaged the engine they would have included that in the estimate. It is not a pleasing experience for a technician to get a disabled vehicle running only to find that the engine is no good. That is when the finger pointing starts, the shop is sometimes then stuck with an abandon vehicle and an unpaid repair bill.