Scan Tool Usage: Notes

NOTE: Before connecting scan tool, follow steps in MALFUNCTION INDICATOR LIGHT CHECK .

NOTE: Information obtained by a scan tool is only as accurate as the scan tool itself. A scan tool that displays faulty data should not be used. If faulty data readings are suspected, verify scan tool information using a DVOM and wiring schematic.

Scan tool is a specialized tester which can diagnose on-board computer control systems by providing almost instant access to circuit data without crawling under instrument panel or engine hood to backprobe sensors and connectors. Scan tools reduce diagnostic time by furnishing input data (sensor values) which can be compared to specification parameters.

Scan tools also furnish status data of output devices (solenoids and motors). However, status parameters are only an indication that output signals have been sent to devices by Engine Control Module (ECM). They do not indicate if devices respond properly to that signal. This must be verified at output device using a DVOM or test light.

If DTCs are not present, a problem may still exist. Driveability-related problems with DTCs displayed occur about 20 percent of the time, while driveability problems without DTCs occur about 80 percent of the time. Out-of-calibration sensors may NOT set a DTC, but WILL cause driveability problems. A scan tool is the easiest method of checking sensor specifications and other data parameters. A scan tool is also useful in finding intermittent wiring problems by wiggling wiring harnesses and connections (key on, engine off) while observing data parameters.