Diagnostic Circuit Check

Fig. 008 - Wiring Diagram for Diagnostic Circuit Check:

DIAGNOSTIC CIRCUIT CHECK

3.8L, 5.0L, & 5.7L

CARBURETED

Circuit Description:
The purpose of the "Non-Scan" Diagnostic Circuit Check is to 1) make sure the "Service Engine Soon" light works, 2) the ECM is operating and can recognize a faulty, and 3) to determine if any codes are stored. If codes are stored, it, also, checks to see if an intermittent problem is indicatd. This is the starting point for any diagnosis. If there are no codes indicated, go to the System Performance Check.
When the engine is started, the ECM grounds terminal "G", to turn out the SES light. It alternately grounds and opens it to flash a code.

Fig. 004 Diagnostic Circuit Check:

Test Description:
Step numbers refer to step numbers on the diagnostic chart.
1. Checks for the proper operation of the "Service Engine Soon" light. With the key "ON", and the engine not running, the light should be on steady.
2. Grounding the test terminal will flash a Code 12 and any stored trouble codes. The light must go "ON" and "OFF", for a proper code. If the light goes from "bright" to "dim", this is not considered a code. See CHART A-6, in that case.
3. This step is to determine if any codes, other than Code 12 that was recorded before, are still present, or were intermittent and are no longer there. Memory is cleared and vehicle run for two minutes, to see if trouble code(s) will reset.
4. If the light is "ON", fault is still present, therefore, go to the applicable trouble code chart.
5. If the light is "OFF", the fault is either intermittent, or it is a code that cannot be set in the stall in two minutes. For codes that cannot be set in the stall during the diagnostic circuit check, the applicable trouble code chart will determine if those codes are intermittent.