Scan Tool Usage

NOTE: Before connecting scan tool to vehicle, diagnostic system should be checked to determine if system is operating properly, and if information received will be accurate. This is done by performing ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK . If vehicle does not pass OBD system check, information received may be invalid.

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

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

If DTC is not present, a problem may still exist. Driveability-related problems with DTC displayed occur about 20 percent of the time, while driveability problems without DTC 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. See SCAN TOOL DATA VALUES table under SCAN TOOL DATA.