The truck rolls in with a diagnostic trouble code light on. The chances are good that the first thing a technician will do is grab a scan tool and see what code or codes have set.
However, it’s important to also remember the most basic diagnostic step: asking questions. Asking the driver questions about the operating conditions when the problem occurred can be immensely helpful in diagnosing fault codes. This is particularly true when confronted with intermittent problems. It is not unusual for a technician to be unable to duplicate a problem, only to have the regular driver duplicate the problem in short order. Asking questions about what was going on when the code set or problem occurred will help diagnose many complaints that would otherwise take more time to isolate.
Another helpful step in diagnosing faults is to check the service history when possible. It is always good to know what has already been tried that either corrected the problem temporarily or resolved nothing. Granted, there are some parts that are prone to failure. Still, when repeated failures are noted it is a good idea to look elsewhere in the system to see what else could be leading that particular part to fail.
Virtually every system has initial inspection steps that are unique to the system. The simple steps of asking questions and checking history are fairly universal. With all the different systems and complexities of today’s vehicles, it is also wise to consult your service information resource, like TruckSeries truck repair information from Mitchell 1, to see if there are specific steps that need to be followed in initial inspections.
Yes, these steps to take time. Nevertheless, the time spent in determining the correct path to an accurate diagnosis and repair not only saves time by avoiding the wrong path that could lead to a comeback, but also builds customer confidence that you can get the truck fixed right the first time.
This article was contributed by Jake Schell, associate product manager for Mitchell 1’s Commercial Vehicle Group.