The code P2609 on a 6.7 Cummins is an indication of an engine misfire. A misfire occurs when the fuel-air mixture within the combustion chamber does not ignite as expected, resulting in a loss of power and performance from the engine. This can occur for several different reasons, such as spark plug or coil malfunction, low fuel pressure, clogged air filter, or vacuum leak. It's important to address this issue right away since it can cause further damage to components like exhaust valves and turbochargers if left unchecked. The first step is to identify what's causing the misfire by retrieving trouble codes on your diagnostic scanner; this will help you pinpoint which area needs attention so you can take corrective action quickly and efficiently.