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Engine Controls - Basic Engine Testing - 3.1L: Diagnosis Oldsmobile Cutlass VI

Testing & Diagnostics ~946 words

VISUAL INSPECTION

Visually inspect all electrical wiring, looking for chafed, stretched, cut or pinched wiring. Ensure electrical connectors fit tightly and are not corroded. Ensure vacuum hoses are properly routed and not pinched or cut. If necessary, see VACUUM DIAGRAMS article to verify routing and connections. Inspect air induction system for possible vacuum leaks.

Diagnosis

  1. Start engine and bring to operating temperature. Increase engine speed to 2000-2500 RPM and note gauge. If reading exceeds 1.25 psi (.09 kg/cm 2 ), exhaust system is restricted.
  2. Check exhaust system for collapsed pipe, heat distress and possible internal muffler failure. If none of these conditions exist, check for restricted catalytic converter. Replace as required.

NO START DIAGNOSIS

Note. Some vehicles are equipped with anti-theft systems (VATS or PASS-Key(R)) which will not allow vehicle to be started if improper starting procedures or improperly coded ignition keys are used. Both fuel injection and cranking systems will be disabled. Loss of fuel enable signal from anti-theft decoder module should set a diagnostic trouble code in PCM memory.

Note. For terminal and circuit ID, see the WIRING DIAGRAMS article.

General Inspection

  1. Ensure proper starting procedure is being used.
  2. Visually check vacuum hoses for splits, kinks and proper connections, as shown on Vehicle Emission Control Information label. Check ignition wires for cracking, hardness and proper connections at both coil pack and spark plugs.
  3. In very cold temperatures, check oil is proper viscosity and not contaminated with gasoline.

ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK

Note. Tech 1 scan tool is required to perform OBD system check.

The OBD System Check determines

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

After performing procedures in PRELIMINARY INSPECTION & ADJUSTMENTS, BASIC FUEL SYSTEM CHECKS and BASIC IGNITION SYSTEM CHECKS, this is the starting point for utilizing the self-diagnostic system for determining computer-related problems. After performing necessary tests as described in the diagnostic circuit check, if no codes are indicated and driveability problems still exist, see the TESTS W/O CODES article and SCAN TOOL USAGE in the TESTS W/CODES article.

  1. Turn ignition on with engine off. Observe Malfunction Indicator Light (MIL). If MIL illuminates, go to next step. If MIL does not illuminate, go to «MIL INOPERATIVE»(ref-20651-S38088625722001010200000) .
  2. Turn ignition off. Install Tech 1 scan tool and follow scan tool manufacturer's instructions to proceed with test. Turn ignition on. If scan tool displays PCM data, go to next step. If scan tool does not display PCM data, go to «DLC DIAGNOSIS OR NO SCAN TOOL DATA»(ref-20651-S25450679332001010200000) .
  3. Attempt to start engine. If engine start and runs, go to next step. If engine does not start, or starts and dies, go to «NO START DIAGNOSIS»(ref-20651-S04651941362001010200000) .
  4. Using scan tool, observe DTC status on LAST TST FAIL function. If any DTC is stored, save freeze frame and fail record information using scan tool CAPTURE INFO feature. If a DTC is indicated as last test failed, diagnose affected DTC. See the TESTS W/CODES article. If DTC is not indicated, go to next step.
  5. Using scan tool, display DTC fail records. If a DTC fail record is stored, save freeze frame and fail record information using scan tool CAPTURE INFO feature. If a fail record is not stored, go to next step. If a fail record is stored, diagnose affected DTC. See the TESTS W/CODES article.
  6. Compare scan tool engine data with actual control system data values. If value is within limits, system is okay. If value is not within limits, go to the SYSTEM/COMPONENT TESTS article.

DLC DIAGNOSIS OR NO SCAN TOOL DATA

  1. Perform On-Board Diagnostic (OBD) System Check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-20651-S05911687882001010200000) . After performing OBD system check, go to next step.
  2. Turn ignition on with engine off. Connect a test light between DLC battery feed circuit and ground circuit. See the WIRING DIAGRAMS article. If test light illuminates, go to step 4). If test light does not illuminate, go to next step.
  3. Using a test light connected to ground, probe DLC battery feed circuit. See the WIRING DIAGRAMS article. If test light illuminates, go to next step 9). If test light does not illuminate, go to step 10).
  4. Turn ignition on with engine off. Using DVOM connected to ground, probe DLC class 2 serial data circuit. See the WIRING DIAGRAMS article. DVOM should read zero volts. If voltage is as specified, go to next step. If voltage is not as specified, go to step 7).
  5. Turn ignition off. Disconnect PCM connector. Turn ignition on with engine off. Using DVOM connected to battery voltage, probe DLC class 2 serial data circuit. See the WIRING DIAGRAMS article. DVOM should read zero volts. If voltage is as specified, go to next step. If voltage is not as specified, go to step 8).
  6. Check for open in class 2 serial data circuit between DLC and PCM. Repair as necessary. After repairs, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-20651-S05911687882001010200000) . If circuit is okay, go to step 11).
  7. Check for short to voltage in class 2 serial data circuit. Repair as necessary. After repairs, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-20651-S05911687882001010200000) . If circuit is okay, go to step 11).
  8. Locate and repair short to ground in class 2 serial data circuit. After repairs, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-20651-S05911687882001010200000) .
  9. Locate and repair open in DLC ground circuits. After repairs, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-20651-S05911687882001010200000) .
  10. Locate and repair open or short to ground in DLC battery feed circuit. After repairs, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-20651-S05911687882001010200000) .
  11. Replace PCM. Perform PCM relearn procedures. After repairs, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-20651-S05911687882001010200000) .

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