RETRIEVING CODES (WITH SCAN TOOL)
Note. Plugging scan tool into DLC enables user to read trouble codes and check voltages in system on serial data line.
Scan tools may also furnish information on status of output devices (solenoids and relays). However, status parameters are only an indication that output signals have been sent to devices by control module; they do not indicate if devices have responded properly to signal. Check for proper response at output device using a voltmeter or test light.
Note. On vehicles equipped with 2.3L engine, Code 12 should always exist when DLC is grounded with Key On and Engine Off (KOEO), but may not be indicated by all makes of scan tools.
If trouble codes are not present, this is not necessarily an indication a problem does not 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. Sensors that are out of specification WILL NOT set a trouble code but WILL cause driveability problems. Using 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 harness and connections (key on, engine off) while observing scan tool.
Note. If erroneous voltage signals are suspected, it will be necessary to verify scan tool information using a digital voltmeter and wiring schematic. If non-existent codes are displayed, turn ignition off, remove scan tool, turn ignition on and ground DLC test terminal "B". (Scheme 78) Same codes flashed by MIL should be indicated by scan tool.