On-Board Diagnostic (OBD) System Check

The OBD system check determines:

• If Malfunction Indicator Light (MIL) operates.
• If PCM is operating and can recognize a fault.
• If any DTCs are stored.

After performing procedures in PRELIMINARY INSPECTION & ADJUSTMENTS, BASIC FUEL SYSTEM CHECKS and BASIC IGNITION SYSTEM CHECKS in appropriate BASIC DIAGNOSTIC PROCEDURES article, this is the starting point for utilizing the self-diagnostic system for determining computer-related problems. After performing necessary tests as described in the OBD system check, if no DTCs are indicated and driveability problems still exist, see appropriate TROUBLE SHOOTING - NO CODES article and SCAN TOOL USAGE .

1. Connect scan tool to 16-pin DLC located under left side of instrument panel. See Fig 1. If scan tool does not power up, check power to DLC. See WIRING DIAGRAMS article. If scan tool powers up, go to next step.
2. Check if scan tool communicates with PCM, go to next step. If scan tool does not communicate with PCM, check if it communicates with BCM. If scan tool does not communicate with BCM, check power to DLC. See WIRING DIAGRAMS article. If scan tool communicates with BCM, go to step  5.
3. Attempt to start engine. If engine starts, go to next step. If engine cranks but does not start, go to step  9. If engine does not crank, diagnose starting system. See appropriate article in STARTING & CHARGING SYSTEMS.
4. Check for DTCs. Diagnose affected DTCs. See DIAGNOSTIC TESTS . If no DTCs are set, see appropriate TROUBLE SHOOTING - NO CODES article.
5. Turn ignition off, wait 10 seconds, then ignition on. Listen for fuel pump or fuel pump relay operation (about 2 seconds). If fuel pump does not operate, go to next step. If fuel pump operates, check instrument panel harness connector. Repair as necessary. If harness connector is okay, replace PCM.
6. Check battery voltage on both sides of CONTROLS B fuse (10-amp) located in underhood fuse block. If battery voltage is present on both sides of fuse, go to next step. If battery voltage is not present on both side of fuse, check for open fuse or circuit between battery and underhood fuse block. Repair as necessary.
7. Turn ignition off. Disconnect PCM harness connector. Turn ignition on. Measure voltage on PCM harness connector J1 terminal No. 60 (Black/White wire). See WIRING DIAGRAMS article. If battery voltage is present, go to next step. If battery voltage is not present, repair open in circuit.
8. Check for continuity between ground and Black/White wire. If continuity exists, check for terminal tightness or faulty PCM. Repair or replace as necessary. If continuity does not exist, check for open in Black/White wire. See WIRING DIAGRAMS article.
9. Turn ignition on, with engine off. Check if any BCM communication or Passlock(R) DTCs are set (P1626, P1630, P1631, P1632 or U1064). If any of these DTC(s) are set, diagnose affected DTC(s). If these DTC(s) are not set, go to next step.
10. Using scan tool, monitor ignition voltage. If voltage reading is not less than 2 volts, go to next step. If voltage reading is less than 2 volts, go to step  16.
11. Check if DTC P0601 or P0602 is set. If any of this DTC is set, diagnose affected DTC(s). If these DTC(s) are not set, go to next step.
12. Check if injector DTCs are set (P0201, P0202, P0203 or P0204). If any of this DTC is set, repair ignition voltage to affected injector. If these DTC(s) are not set, go to next step.
13. Check if DTC P0107, P0108, P0122, P0123, P0452, P0453 or P0530 is set. If any of this DTC is set, diagnose affected DTC(s). If these DTC(s) are not set, go to next step.
14. Crank engine. Using scan tool, check is CKP active counter is incrementing. If CKP active counter is incrementing, go to next step. If CKP active counter is not incrementing, go to step  18.
15. Set scan tool to CAL. COMPRESSION OUTPUT. Check if "1s" is displayed on scan tool. If "1s" is displayed, go to step  26. If "1s" is not displayed, go to step  33.
16. Check IGN 1 fuse (10-amp) located in underhood fuse block. If fuse is okay, go to next step. If fuse is blown, check circuit (Pink wire) between fuse block and PCM. See WIRING DIAGRAMS article. Repair as necessary.
17. Turn ignition off. Disconnect PCM harness connector. Using DVOM, check voltage between ground and circuit (Pink wire) between fuse block and PCM. See WIRING DIAGRAMS article. If battery voltage is present, check for terminal tightness or faulty PCM. Repair as necessary. If battery voltage is not present, check for open in circuit. Repair as necessary.
18. Turn ignition off. Disconnect Electronic Ignition (EI) module harness connector. Turn ignition on, with engine off. Measure voltage between ground and EI module harness connector terminal "A" (Pink wire). If battery voltage is present, go to next step. If battery voltage is not present, check EIS fuse (10-amp) located in underhood fuse block or circuit between fuse block and EI module. See WIRING DIAGRAMS article. Repair as necessary.
19. Measure voltage between EI module harness connector terminal "A" (Pink wire) and terminal "E" (Black wire). If battery voltage is present, go to next step. If battery voltage is not present, check for open in EI harness connector terminal "E" (Black wire) circuit. Repair as necessary.
20. Set scan tool to CKP ACTIVE COUNTER. Using a test light connected EI module harness connector terminal "C" (Purple/White wire), momentarily touch end of test light to battery negative terminal, then to positive battery terminal. Observe scan tool display. If CKP active counter increments, go to next step. If CKP active counter does not increment, check circuit (Purple/White wire) for open or terminal tightness. Repair as necessary. If circuit is okay, replace PCM.
21. Check resistance between EI harness connector terminals "H" (Yellow wire) and "J" (Purple wire). See WIRING DIAGRAMS article. If resistance is 500-900 ohms, go to next step. If resistance is less than 500 ohms, go to step  24. If resistance is greater than 900 ohms, go to step  25.
22. Disconnect Crankshaft Position (CKP) sensor harness connector. Check for continuity between ground and EI module harness connector terminal "H" (Yellow wire). If continuity exists, repair grounded circuit. If continuity does not exist, go to next step.
23. Reconnect CKP sensor harness connector. Using DVOM in AC scale, connect DVOM between EI harness connector terminals "H" (Yellow wire) and "J" (Purple wire). Crank engine. If voltage reading is greater than 200 millivolts, check for terminal tightness at harness connectors. Repair as necessary. If terminals are okay, replace EI module. If voltage reading is not greater than 200 millivolt, check CKP sensor for proper installation. Sensor mounting bolt should be tightened to 89 INCH lbs. (10 N.m). If torque is okay, replace sensor.
24. Disconnect Crankshaft Position (CKP) sensor harness connector. Check for continuity between EI module harness connector terminals "H" (Yellow wire) and "J" (Purple wire). See WIRING DIAGRAMS article. If continuity exists, repair shorted circuit. If continuity does not exist, replace CKP sensor.
25. Disconnect Crankshaft Position (CKP) sensor harness connector. Check for open in EI module harness connector terminals "H" (Yellow wire) and "J" (Purple wire). See WIRING DIAGRAMS article. Repair as necessary. If circuits are okay, replace CKP sensor.
26. Turn ignition off. Connect Fuel Pressure Gauge (SA9127E) to fuel rail test port. Turn ignition on. Fuel pressure should be 50-60 psi (345-414 kPa). If fuel pressure is as specified, check fuel for quality problem. If fuel pressure is not as specified, go to next step.
27. Turn ignition off. Remove fuel pump relay located in left passenger compartment fuse/relay block. Using a fused jumper wire, jumper relay circuits No. 120 (Gray wire) and No. 1140 (Orange wire) in fuse/relay block. See WIRING DIAGRAMS article. Observe fuel pressure gauge. If fuel pressure is present, go to next step. If fuel pressure is not present, go to step  30.
28. Remove jumper wire. Connect a test light between ground and fuel pump relay circuit No. 465 (Green wire) in fuse/relay block. Using scan tool, command fuel pump relay on. If test light illuminates, go to next step. If test light does not illuminate, check circuit for open/short to ground or for terminal tightness. Repair as necessary. If circuit or terminals are okay, replace PCM.
29. Connect test light between fuel pump relay circuits No. 465 (Green wire) and No. 550 (Black wire) in fuse/relay block. See WIRING DIAGRAMS article. Using scan tool, command fuel pump relay on. If test light illuminates, replace fuel pump relay. If test light does not illuminate, repair open in Black wire.
30. Remove jumper wire. Connect a test light between ground and fuel pump relay circuit No. 1140 (Orange wire) in fuse/relay block. See WIRING DIAGRAMS article. If test light illuminates, go to next step. If test light does not illuminate, check fuel pump fuse located in underhood fuse block. If fuse is blown, check for short in circuit or fuel pump. Repair as necessary. If circuit is okay, check for open in Orange wire between underhood and left passenger compartment fuse/relay block.
31. Turn ignition off. Disconnect fuel pump assembly harness connector. Reinstall fused jumper wire between fuel pump relay circuits No. 120 (Gray wire) and No. 1140 (Orange wire) in fuse/relay block. Connect test light between ground and fuel pump relay circuit No. 120 (Gray wire). If test light illuminates, go to next step. If test light does not illuminate, repair open circuit.
32. Connect test light between fuel pump relay circuits No. 120 (Gray wire) and No. 550 (Black wire) in fuse/relay block. If test light illuminates, replace fuel pump motor. If test light does not illuminate, repair open circuit.
33. Turn ignition off. Remove EI module from ignition coil housing. Check for continuity for terminal tightness at EI module connector and interconnect between module and ignition coil. If terminals are okay, check EI module or ignition coil. See appropriate SYSTEM & COMPONENT TESTING article. Replace module or ignition coil as necessary.

Fig 1: Identifying OBD-II Data Link Connector (DLC)

Courtesy of GENERAL MOTORS CORP.