Modern Engine Diagnostics
Before 2007, engine diagnostics checks were relatively simple. You could evaluate the seriousness of an engine problem by simply looking at the exhaust smoke. If the smoke was white, you likely had a coolant or fuel problem. If you observed dark black smoke, you certainly had a fuel problem. Blue tinted smoke would likely indicate an oil issue.
Those good old days are gone and now we must rely on more sophisticated techniques. Today, any smoke from the exhaust, means you have an after-treatment defect, but that is likely the beginning of your woes.
You may also have a cracked DPF substrate, and many times that crack is from an overheated exhaust. It would be great if we could stop there, but unfortunately the overheated exhaust came from an upstream defect with the engine or perhaps as simple as a leaking exhaust system.
Modern diagnostic techniques include hooking up a diagnostic tool with sophisticated software. Without analyzing fault codes and monitoring data points it would be very difficult, and perhaps impossible to determine the root cause of these problems.
Now we lean on digital multi-meters and oscilloscopes to properly troubleshoot these truck and engine systems. So, modern technicians have traded in their old test lights, and pulled out the meters and scopes for the future.