There was a catastrophic engine failure of a 2021 Colorado 3.6L V6 engine. The engine has been replaced by GM and the failed engine is in the dealers’ possession. While driving on a congested street, the engine misfired and immediately stopped. The vehicle rolled to a stop in the middle of 3 lanes. Occupants had to flag down traffic while pushing vehicle to the side. There was no warning lamps, messages or other symptoms, such as knocking, prior to the failure; and the oil service was maintained per manufacturer. Two separate dealers found ‘piston to valve contact, top of piston severely damaged, and metalic debris in intake plenum.’ GM Service Bulletin 19-NA-256 has identified ‘Seized engine’ caused by defective ‘crankshaft main or rod bearing failure’ that can put the oil filter ‘in by-pass and distribute unfiltered oil with bearing debris throughout the engine.’ In addition to the rod bearings, designated inspection points are the cam caps and camshaft journals on the heads and the timing change idler sprocket for stiffness when turning. Since the vehicle was 15,000 miles over the 60K warranty, they would not perform the designated diagnostic steps in Service Bulletin. Owner waiting on independent oil analysis. Service department provided pictures of metallic debris and valve damage, as well as the damaged spark plug. After opening Case # 9-14977425869 with GM Customer Service and asking why Warranty has not been extended or a Recall issued for the known manufacturer defect in the TSB, the response was ‘it likely has not occurred enough times to warrant a recall’. With a dealer discount, total towing, diagnostic and repair costs exceed $11,000. Results of Blackstone Labs oil analysis will be provided when completed, however, the oil was just changed 462 miles prior to the failure, so a sample of the previous oil that would have contributed the most to the failure was not available (6,948 mi on previous oil).