On-Board Diagnostic II (OBD-II) System Check

The On-Board Diagnostic II (OBD-II) System Check is the starting point for any driveability complaint diagnosis. Before any DTC(s) are retrieved, perform a visual underhood inspection checking battery and grounds for clean and tight connections. Check for poor connections or damage to wiring harness and electrical connectors. Check for corroded terminals or corrosion build-up on any connection. Repair as necessary. The OBD-II system check is an organized approach to identifying problems created by an electronic engine control system malfunction.

Use of Tech 2 scan tool is required to perform ON-BOARD DIAGNOSTIC II (OBD-II) SYSTEM CHECK. To reprogram EEPROM or to program PCM after it has been replaced, see COMPUTER RELEARN PROCEDURES article in GENERAL INFORMATION section.

1. Turn ignition on with engine off. Verify Malfunction Indicator Light (MIL) is on. If MIL is on, go to next step. If MIL is not on, go to BASIC TESTING article.
2. Turn ignition off. Install Tech 2 scan tool. Turn ignition on. If scan tool displays PCM data, go to next step. If scan tool does not display PCM data, verify scan tool is properly installed. If scan tool is properly installed, go to step  8 .
3. Using scan tool, command MIL OFF. If MIL turns off, go to next step. If MIL does not turn off, go to BASIC TESTING article.
4. Start engine. If engine starts and continues to run, go to next step. If engine will not run, go to BASIC TESTING article.
5. Using scan tool, check if any DTCs have been set. If any DTCs are set, go to next step. If no DTCs are set, go to step  7 .
6. Are 2 or more of the following DTC(s) stored?
   • P0107
   • P0108
   • P0113
   • P0118
   • P0122
   • P0123
   • P0712
   • P1392
   • P1406

   If 2 or more of these codes are stored, go to BASIC TESTING article. If a single DTC is stored, go to DIAGNOSTIC TROUBLE CODE DEFINITIONS  to identify DTC and proceed to the appropriate DTC test under CIRCUIT TESTS.

7. Compare PCM data values displayed to typical engine scan data values. See appropriate SCAN TOOL DATA VALUES table under PIN VOLTAGE (VALUE) TESTS in PIN VOLTAGE CHARTS article. If values displayed are normal or close to typical values, OBD-II system check is complete. If driveability problem still exists, go to TESTS W/O CODES article. If values are not correct, go to SYSTEM/COMPONENT TESTS article.
8. Turn ignition off. Disconnect PCM connectors. Turn ignition on with engine off. Check for open or short in class 2 data circuit (Orange/Green wire) between Data Link Connector (DLC) terminal No. 2 and PCM 32-pin connector C-1, terminal B13. Also check for open or short in ignition feed circuit (Green/White wire) between DLC terminal No. 16 and dash fuse box. Also check for open in ground circuit (Black wire) to DLC terminal No. 4. If problem is found, repair as necessary and return to step 2). If no problem is found, go to next step.
9. Attempt to reprogram EEPROM. Programming PCM/EEPROM requires the use of a scan tool and special manufacturer equipment. Attempt to display PCM data on scan tool. If data is now displayed, return to step 2). If data is not displayed, go to next step.
10. Replace PCM. Program PCM. After repair, return to step 2).