When diagnosing a system which relies on the operation of a control module using the class 2 serial data circuit, a scan tool may be used to view data which affects system operation. A control module usually relies on several inputs to carry out a certain output function. System operation may be determined by input devices such as switches or sensors wired directly to the control module which is performing an output function. A control modules output functions may also be affected by information provided by other control modules using the serial data circuit. A scan tool can provide access to this information and may be necessary to determine why a system malfunction exists.

Use the scan tool to display the status of inputs to a particular control module. This feature is helpful in determining whether input devices such as switches or sensors are operating properly or if the control module is able to correctly interpret the input signals.

Use the scan tool to activate a particular control modules output functions. A command from the scan tool to cycle an output function will be performed regardless of any specific program instructions or inputs which would normally prevent the function from occurring. This feature is helpful in determining whether output devices such as relays, actuators, or motors will operate properly or if the control module is capable of carrying out a certain output function.