Welcome back for part two of advanced circuit diagnostics. We are going to take a look at some live scope captures taken from circuit defects installed on a test board.

The advanced circuit diagnostics I will be explaining will require a three-part study. Part one will show the two contained advanced circuit diagnostic charts that you can keep both for study now and in the future to help organize your thoughts and analyze your test results on actual vehicles.

The Ford IDS is a PC-based factory scan tool software package that utilizes a Vehicle Communication Module (VCM), an interface to connect a PC to the vehicle's Diagnostic Link Connector (DLC). The IDS has become a very popular purchase in aftermarket repair shops for good reason. This month we will look at one of the most useful features this tool has — the LIVE misfire graph. This feature, while very useful, is often misunderstood because of the way the information is presented and graphed. Let's try and clear this up.

This month, we will discuss an often overlooked cause of loss of communication with a powertrain control module (PCM). Many techs have been trained to first check a non-communicating module for proper power feeds and grounds. In addition, techs were taught to verify defect-free communication wires to the PCM and to check for short circuits in all the output solenoids the PCM controls. If all four of those requirements are met, they should replace the module.

Scan tool manufacturers on bothe the aftermarket and OEM sides have stepped up to the place to make diagnostics more efficient. But understanding how systems work will help you in your diagnosis of vehicle problems.

Chrysler's Star Mobile PC-based scan tool offers a number of diagnostic functions, including a CAN-C Bus Test and Advanced LoC screen.

The DRBIII (Diagnostic Readout Box 3) scan tool uses specific functions to diagnose Chrysler PCI (Programmable Communication Interface) Bus system.

This month's scan tool network diagnostic article will center on Chrysler's DRBIII (Diagnostic Readout Box 3) scan tool. While the DRBlll communicates with several vehicle network data protocols, we are going to cover just the two network protocols for which the DRBIII has specific diagnostics functions.

Starting in 2004, some GM vehicles began using a new data network system called GMLAN. GMLAN networks use a new "Node Management Strategy." GMLAN is different from the older Class 2 network strategy where modules wake up and send a State Of Health (SOH) message approximately every two seconds. With GMLAN, only the modules involved in a given Virtual System of modules are "awake" and communicating at the appropriate time.