Diagnostic Circuit Check

Diagnostic Circuit Check:

Diagnostic Circuit Check:

DIAGNOSTIC CIRCUIT CHECK


Circuit Description:

The purpose of the Diagnostic Circuit Check is to

1) make sure the "SERVICE ENGINE SOON" light works,

2) the ECM is operating and can recognize a fault, and

3) to determine if any codes are stored. If codes are stored, it also checks to if they indicate an intermittent problem. This is the starting point for any diagnosis. If there are no codes indicated, go to the System Performance Check. If no additional checks are called out from the System Performance Check, see Diagnosis By Symptoms - No Trouble Codes Stored.


Test Description:

1. Check for proper operation of the "SERVICE ENGINE SOON" light with the key "ON," 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.