Scan Tool Usage

NOTE: Before connecting scan tool, check diagnostic system and ensure accurate information is received by scan tool. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in BASIC TESTING article. If vehicle does not pass On-Board Diagnostic (OBD) system check, information received by scan tool may be invalid.

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 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/TCM. 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 trouble codes are not present, a problem may still exist. Driveability-related problems with codes displayed occur about 20 percent of the time, while driveability problems without codes occur about 80 percent of the time. Out-of-calibration sensors WILL NOT set a trouble code, but WILL cause driveability problems. 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 DATA VALUES table.

NOTE: Information obtained by scan tool is only as accurate as the scan tool itself. If erroneous voltage signals are suspected, verify scan tool information using a digital voltmeter and wiring schematic.