Diagnostic Circuit Check

Chart A-0 - Diagnostic Circuit Check:

Procedure for Chart A-0 Diagnostic Circuit Check - Drivability, & ECM Trouble Code Diagnosis:

DIAGNOSTIC CIRCUIT CHECK

The Diagnostic Circuit Check must be the starting point for any driveability complaint diagnosis.

The Diagnostic Circuit Check is an organized approach to identifying a problem created by an Electronic Engine Control System malfunction because it directs the Service Technician to the next logical step in diagnosing the complaint. It's proper understanding and correct useage will reduce diagnostic time and prevent unnecessary parts replacement.

The "ECM Data" listed in the table above, may be used for comparison after completing the Diagnostic circuit Check and finding the on-board diagnostics functioning properly and no trouble codes displayed. The "Typical Values" listed for "ECM Data" are an average of display values recorded from normally operating vehicles and are intended to represent what a normally functioning system would typically display. Actual values may vary from one vehicle to the next, therefore these "Typical Values" should be used as only an indication as to which portion of the Electronic Engine Control System should be investigated further.

The "ECM Discrete Inputs" selection displays the voltage state for the selected input circuit at it's ECM terminal. An "X" will appear next to the "HI/LO" display indicating that one change of state has occured once during the period that the selection was displayed.

The "ECM Output Cycling" selection displays the commanded state of the ECM output driver circuit for the selected device, but only while the engine is stopped. This commanded state will cycle "LO" (On) to "HI" (Off) at three second intervals on all outputs. When IAC is selected, the IAC pintle is extended out against it's seat to permit a minimum air rate adjustment to be made.

Clearing Trouble Codes see appropriate section