On-Board Diagnostic (OBD) System Check

On-Board Diagnostic (OBD) System Check is an organized approach in identifying a problem created by an electronic engine system malfunction. It must be the starting point for any driveability complaint diagnosis, because it directs service technician to next logical step in diagnosing a complaint. Understanding and using it correctly will reduce diagnostic time and prevent unnecessary replacement of good parts. DO NOT  perform this check if a driveability concern in not present.

1. Check for one or more of the following conditions:
   • Malfunction Indicator Light (MIL) on with engine running.
   • Confirmed customer driveability concern.
   • Suspected fault in computerized engine control system.

   If any conditions are present, go to next step. If specified conditions are not present, system is okay at this time. Check for an intermittent problem. See INTERMITTENTS in the TESTS W/O CODES article.

2. Turn ignition on. Observe MIL. If MIL comes on, go to next step. If MIL does not come on, go to CIRCUIT TEST A1-1 .
3. Turn ignition off. Connect scan tool according to manufacturer's instructions. Turn ignition on. If scan tool displays PCM data, go to next step. If scan tool does not display PCM data, go to CIRCUIT TEST A1-4 .
4. Attempt to start engine. If engine starts and runs, go to next step. If engine will not run, go to CIRCUIT TEST A1-3 in the BASIC TESTING article.
5. Observe DTC data. If no DTCs are set, go to next step. If any DTCs are set, save freeze frame data using scan tool and go to appropriate CIRCUIT TEST or DTC TEST.
6. If MIL is on, and no DTCs are set, go to CIRCUIT TEST A1-2. If MIL is off and no DTCs are set, go to next step.
7. Compare scan tool data with values shown in SCAN TOOL DATA VALUES  table under SCAN TOOL DATA. If displayed values are within specified ranges, suspect an intermittent fault. See INTERMITTENTS in the TESTS W/O CODES article. If displayed values are not within specified ranges, see the SYSTEM/COMPONENT TESTS article.