Diagnostic Circuit Check - With Diagnostic Scan Tool
"Scan" Diagnostic Circuit Check:
Wiring Diagram For "Scan" Diagnostic Circuit Check:
"SCAN" DIAGNOSTIC CIRCUIT CHECK
The "SCAN" Diagnostic Circuit Check is an organized approach for identifying fuel injection problems using an assembly line communication link (ALCL). This communication link can provide diagnostic information for display on any "SCAN" device or tool designed for this purpose.
The use of a "SCAN" device requires a good understanding of its operation as well as its limitation. A complete review of the instruction manual furnished with the tool as well as the Introduction and General Description in this section is very important.
The tool plugs into the ALCL connector located below the instrument panel. If a stored code is displayed, the code definitions located under DEFINITION OF CODES will aid in determining if the fault is still present (hard failure) or the result of an intermittent condition not normally diagnosed using the code charts.
A hard failure will be diagnosed using charts that have been developed for both "SCAN" and "NON-SCAN" diagnosis. "SCAN" steps start with the arrow marked "Start Scan" and are identified by the larger type. The actual repair procedures, however, are the smaller type and apply to both methods of diagnosis.
The facing page of each chart will provide a general circuit description and in some instances, alternate diagnostic steps or other diagnostic aids specific to that chart.
1. If the "SCAN" tool is not operating, check on another vehicle. If OK, the cigar lighter socket should be checked for 12 volts and a good ground. If the "SCAN" tool reads "no data" or "no ALCL", with the ignition "on", check the serial data wire for an open or short to ground between ALCL terminal "E" and the ECM.
Also, check for an open diagnostic terminal from ALCL terminal "B" and ECM. With ignition on, the serial data line (ALCL terminal "E") should have a varying 2-5 volts and the diagnostic line (ALCL terminal "B") about 5 volts.