First is that the non-reporting control units can be filtered out by some scan tools. Although it is rare, you must be aware of it when using a scan tool independently or relying on a service.
This is normally caused by an impact at or near the area of the control unit, damaged wiring harness, connector damage, blown fuses or poor ground connections.
Another reason is due to a busy automotive network or the control unit returning information slowly because of a large amount of data stored in that module. Modules have timing parameters that must be adhered to, and at times while they are returning large trouble code records, that request can time out and the scan tool will move on and possibly miss something.
This is when it is necessary to check systems individually on a vehicle or go back and rerun a scan multiple times to make sure everything was received. Both OEM and aftermarket scan tools can be subject to this and is why there are so many update requirements with scan tools.
Q: Why should repairers be aware of the build list in the software’s internal database?
A: When you are reading the scan tool data, be aware that the wrong options can sometimes be reported in the scan tool database. Where we usually see this happen is when there are added accessories or option modifications done by the dealership or the aftermarket. An example is if a customer wants foglamps installed at the dealership; these will not be included in the vehicle option content list and may or may not be accessible by a scan tool. As a result, you must do an inspection and pay close attention to what optional equipment is included.
Q: How can they overcome these issues?
A: DTCs are just the starting point of drilling down the problem(s) on a vehicle. Each system is made up of a group of components, and it’s important to be aware of them during the diagnosis. We call it Component Level Scanning (CLS). This is much different than just reading trouble codes. With CLS, we get as close to the raw or live data as possible.