On-Board Diagnostic (OBD) System Check
NOTE:
DO NOT
perform this check if a driveability complaint is not present.
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 the 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.
- Check for one or more of the following conditions:
- Malfunction Indicator Light (MIL) illuminated 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 TROUBLE SHOOTING - NO CODES article in ENGINE PERFORMANCE.
- Turn ignition on with engine off. Observe MIL. If MIL illuminates, go to next step. If MIL does not illuminate, go to MALFUNCTION INDICATOR LIGHT (MIL) INOPERATIVE under CIRCUIT TESTS.
- Turn ignition off. Install scan tool according to manufacturer's instructions. Turn ignition on with engine off. If scan tool displays PCM data, go to next step. If scan tool does not display PCM data, go to DATA LINK CONNECTOR (DLC) DIAGNOSIS under CIRCUIT TESTS.
- Attempt to start engine. If engine starts and runs, go to next step. If engine will not run, diagnose and repair engine. See BASIC DIAGNOSTIC PROCEDURES article in ENGINE PERFORMANCE.
- Observe DTC data. If no DTC is set, go to next step. If any DTC is set, save freeze frame data using scan tool, and go to appropriate Diagnostic Trouble Code (DTC). See DIAGNOSTIC TESTS .
- If MIL is illuminated and no DTC is set, go to MALFUNCTION INDICATOR LIGHT (MIL) REMAINS ON under CIRCUIT TESTS. If MIL is off and no DTC is set, go to next step.
- 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 TROUBLE SHOOTING - NO CODES article in ENGINE PERFORMANCE manual. If displayed values are not within specified ranges, diagnose suspect component. See SYSTEM & COMPONENT TESTING article in ENGINE PERFORMANCE.