GM Says Black Smoke Normal
This bulletin applies to all 2008-2019 GM passenger cars and light trucks equipped with direct fuel injection systems. Some customers may comment about black smoke, rough idle and minimal misfires on a cold start, and the MIL may not be illuminated.
With the introduction of direct fuel injection, GM has revised the cold start control system to reduce cold-start emissions. Quicker catalytic converter heating helps meet the ever-changing emissions requirements and improve fuel economy.
According to GM, a dual-pulse injection strategy is utilized during engine cold start to reduce the time required to bring the catalytic converter up to operating temperature. This dual-pulse injection strategy lasts for about 60 seconds on cold start. This process will cause the customer to see increased black smoke, soot, rough idle or minimal misfires during cold start and “should be considered normal.”