Scan Tool Usage

Scan tool is a specialized tool which can diagnose on-board computer control systems by providing almost instant access to circuit voltage information without crawling under dash or hood to backprobe sensors and connectors. Scan tools reduce diagnostic time by furnishing input data (voltage signals) which can be compared to specification parameters. See TYPICAL TECH 1 or 2 DATA VALUES table.

Scan tools also furnish information on output device (solenoids and motors) status. However, status parameters are only an indication output signals have been sent to devices by the PCM. They do not indicate whether devices respond properly to that signal. This must be verified at output device using a DVOM or a test light.

If DTC(s) are not present, a problem may still exist. Driveability-related problems with DTC(s) displayed occur about 20 percent of the time, while driveability problems without DTC(s) occur about 80 percent of the time. Out-of-calibration sensors WILL NOT set a DTC, but WILL cause driveability problems. Using a scan tool is the easiest method of checking sensor specifications and other data parameters. Scan tool is also useful in finding intermittent wiring problems by wiggling wiring harnesses and connections (key on, engine off) while observing data parameters. See TYPICAL TECH 1 OR 2 DATA VALUES  table.