- Powertrain/On-Board Diagnostic System Check

OBD System Check Chart:

MIL And DLC Circuit:

CIRCUIT DESCRIPTION
The Diagnostic System Check is an organized approach to identifying a problem created by an electronic engine control system malfunction. It must be the starting point for any driveability complaint diagnosis, because it directs the service technician to the next logical step in diagnosing the complaint. Understanding the chart and using it correctly will reduce diagnostic time and prevent the unnecessary replacement of good parts.

TEST DESCRIPTION
The numbers below refer to circled numbers on the diagnostic chart.

1. This step is to determine if the Tech 1 (or equivalent) scanner can establish communication with the Powertrain Control Module (PCM). If there is no communication between the PCM and the Tech 1 scanner, no data will be displayed.
2. Comparison of actual control system data with the typical values is a quick check to determine if any parameter is not within limits. Keep in mind that a base engine problem may substantially alter sensor values.
3. Installation of a scan tool will provide a ground path for the PCM and may hide a driveability complaint due to poor PCM grounds.
4. If multiple Diagnostic Trouble Codes (DTCs) are stored, start with the lowest numbered DTC first, unless DTC chart indicates not to.
5. If the actual data is not within typical values established, the "C Charts" in "Diagnostic Charts" will provide a functional check of the suspect component or system.

DIAGNOSTIC AIDS
- This vehicle is equipped with a PCM utilizing Electrically Erasable Programmable Read Only Memory (EEPROM).
- When diagnostics call for replacement of the PCM, the new PCM must be programmed.