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Engine Controls Troubleshooting - No Codes - 3.1l Buick Century VI

Testing & Diagnostics ~9821 words

INTRODUCTION

Before diagnosing symptoms or intermittent faults, perform DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article. Use this article to diagnose driveability problems when a current DTC is not present.

Symptom checks are intended to direct the technician to malfunctioning component(s) so that further diagnosis may be performed. A symptom should lead to further testing of specific components or systems, or verification of adjustment specifications.

Use intermittent test procedures to locate intermittent driveability problems that do not occur when the vehicle is being tested. These problems may cause a noticeable driveability problem or cause the Malfunction Indicator Light (MIL) to illuminate on some vehicles.

It is also possible that certain driveability concerns have been rectified by the manufacturer through reprogramming the PCM. Check with manufacturer for latest information on updated programs.

Note. For specific testing procedures, see SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article. To verify specifications, see ON-VEHICLE ADJUSTMENTS - CARS article, or SERVICE & ADJUSTMENT SPECIFICATIONS article.

PRELIMINARY INSPECTION

Note. Manufacturer does not provide testing procedures for many individual systems and components. For system testing not listed, perform related DTC testing procedure. See SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article.

  1. Refer to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) before starting.
  2. Verify on-vehicle diagnostics are working by performing «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  3. Observe the owners driving habits, if possible.
  4. Ensure that the driver understands the transmission Torque Converter Clutch (TCC), and the A/C compressor operation as necessary for appropriate symptom, as explained in the owners manual. Inform the customer how TCC and the A/C clutch operates.
  5. Search for Technical Service Bulletins (TSBs).
  6. Ensure PCM grounds are clean, tight, and properly located.
  7. Check vacuum hoses for splits, kinks, leaks, restrictions and proper connections. Ensure vacuum hoses are correctly routed as shown on vehicle emission control information label.
  8. Check for air leaks at all intake manifold sealing surfaces.
  9. Check ignition wires for cracking, hardness, proper routing and carbon tracking.
  10. Check wiring for proper connections and routing, pinches, burns, cuts or other damage.
  11. Ensure PCM and MIL are functioning properly.
  12. Ensure there are no DTCs stored, or only intermittent DTCs are present.
  13. Ensure that the scan tool data is within normal operating range.
  14. Ensure fuel control system is operating properly. See «FUEL SYSTEMS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-31l__fuel-systems) in BASIC DIAGNOSTIC PROCEDURES - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  15. Perform fuel system pressure test. See «FUEL SYSTEM DIAGNOSIS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-31l__fuel-system-diagnosis) under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  16. Perform a careful visual inspection of all systems.

After all checks have been performed, verify customer complaint and locate correct symptom. Check items indicated under that symptom. Not all items listed under each symptom apply to all models and systems. These procedures will normally recommend testing of a specific system or component, such as EGR, ignition, TCC, etc. See SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article for test procedures.

Note. If PCM displays data but engine fails to start, see NO-START DIAGNOSIS in BASIC DIAGNOSTIC PROCEDURES - 3.1L CENTURY, GRAND PRIX & MALIBU article.

SYMPTOMS

Before proceeding with any symptom diagnosis, perform all steps under PRELIMINARY INSPECTION .

SYMPTOM DIAGNOSIS

Symptom checks should not be used unless symptom occurs while vehicle is being tested. To reduce diagnostic time, ensure steps in BASIC DIAGNOSTIC PROCEDURES - 3.1L CENTURY, GRAND PRIX & MALIBU and SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU articles were performed before diagnosing a symptom. Symptoms available for diagnosis include

  1. «CUTS OUT, MISSES»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l)
  2. «DETONATION/SPARK KNOCK»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l)
  3. «ENGINE BACKFIRES»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l)
  4. «ENGINE DIESELING/RUN-ON»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l)
  5. «HARD START»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l)
  6. «HESITATION, SAG OR STUMBLE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l)
  7. «LACK OF POWER, SLUGGISH OR SPONGY»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l)
  8. «POOR FUEL ECONOMY»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l)
  9. «POOR FUEL FILL QUALITY»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l)
  10. «ROUGH, UNSTABLE OR INCORRECT IDLE & STALLING»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l)
  11. «VEHICLE SURGES OR CHUGGLES»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l)

Symptom Definition

Cuts out or misses is a steady pulsation or jerking which follows engine speed and is usually more pronounced as engine load increases. Exhaust may have a steady spitting sound at idle or low speed. Perform a careful visual inspection as described in PRELIMINARY INSPECTION & ADJUSTMENTS in BASIC DIAGNOSTIC PROCEDURES - 3.1L CENTURY, GRAND PRIX & MALIBU article.

Fuel System

  1. Check the fuel system circuits for proper operation. See «FUEL PUMP ELECTRICAL CIRCUIT DIAGNOSIS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-31l__fuel-pump-electrical-circuit-diagnosis) under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  2. Check for low fuel pressure. See «FUEL SYSTEM DIAGNOSIS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-31l__fuel-system-diagnosis) under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  3. Check for faulty fuel injectors. See «FUEL INJECTOR BALANCE TEST WITH SPECIAL TOOL»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) , «FUEL INJECTOR BALANCE TEST WITH TECH 2»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) and «FUEL INJECTOR COIL TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) under FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  4. Check for fuel contamination. See «ALCOHOL/CONTAMINANTS-IN-FUEL DIAGNOSIS W/O SPECIAL TOOL»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) or «ALCOHOL/CONTAMINANTS-IN-FUEL DIAGNOSIS W/ SPECIAL TOOL»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) under FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  5. Check any items which may cause an engine to run rich, long term fuel trim is significantly in the negative range. See «DIAGNOSTIC AIDS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) for DTC P0172: FUEL TRIM SYSTEM RICH under DIAGNOSTIC TESTS in SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  6. Check any items which may cause an engine to run lean, long term fuel trim is significantly in the positive range. See «DIAGNOSTIC AIDS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) for DTC P0171: FUEL TRIM SYSTEM LEAN under DIAGNOSTIC TESTS in SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article.

Sensor/System

  1. Check for conditions which may cause an incorrect idle speed: Throttle body tampering, excessive deposits, or damage. Restricted air intake system. Large vacuum leak. Check the air intake ducts for being collapsed, damaged areas, looseness, improper installation, or leaking especially between the Mass Airflow (MAF) sensor and the throttle body.
  2. Check the Throttle Position (TP) sensor and related circuit wiring. See to «DTC P0123: THROTTLE POSITION SENSOR CIRCUIT - HIGH VOLTAGE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__dtc-p0123-throttle-position-sensor-circuit) under DIAGNOSTIC TESTS under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  3. Monitor the 24X crank sensor and the Camshaft Position Sensor (CMP) sensor signal present parameters on the scan tool. If both are not responding, test the sensor feed circuit. Both sensors use a separate feed circuit but are internally connected to power. Check all CKP sensor "A" and CMP sensor circuits for intermittents. See «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) .
  4. Check the CKP sensor "B" for an internal short. See «ELECTRONIC IGNITION SYSTEM DIAGNOSIS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l__electronic-ignition-system-diagnosis) under IGNITION SYSTEMS in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  5. Check the Exhaust Gas Recirculation (EGR) system for proper operation. See «EXHAUST GAS RECIRCULATION»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l__exhaust-gas-recirculation) under EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  6. Check the Positive Crankcase Ventilation (PCV) valve for proper operation. See «POSITIVE CRANKCASE VENTILATION»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) under EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  7. Check the transaxle range switch input with the vehicle in Drive and the gear selector in Drive or Overdrive.
  8. Check the following for damage: Bent balancer interrupter rings. Damaged crankshaft position sensor.

Ignition System

Check for proper ignition voltage output using the following steps

  1. Attach Spark Tester (J 26792) to engine ground.
  2. Connect the spark plug end of the spark plug wire to the spark tester. Connect the other end of the spark plug wire to the coil being tested.
  3. Connect the spark plug end of the companion spark plug wire to ground. The companion spark plug wire is the wire attached to the corresponding coil tower.
  4. Crank the engine while observing the spark tester. A spark should be observed.
  5. Repeat steps 1 - 4 for each coil.

If spark is not present at the coils, check for the following conditions

  1. Coils - Cracks, carbon tracking/arcing, or a resistance value outside 5-8 k/ohms.
  2. Spark Plug Wires - Signs of arcing, cross firing, cracks, carbon tracking, plug boot damage, pinched, improper routing, or a resistance value outside 3000 ohms per foot (9868 ohms per meter). Spraying the secondary ignition wires with a light mist of water may help locate an intermittent condition. Ignition voltage arcs to ground when a secondary component is faulty.
  3. Defective Ignition Module - See «ELECTRONIC IGNITION SYSTEM DIAGNOSIS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l__electronic-ignition-system-diagnosis) under IGNITION SYSTEMS in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  4. Ignition System Wiring - Loose ignition module feed or ground connection, or damaged system wiring.

Remove spark plugs and check for the following conditions

  1. Fouled plugs.
  2. Cracks.
  3. Wear.
  4. Improper gap.
  5. Burned or damaged electrodes.
  6. Improper heat range or reach.

If spark plugs are gas or oil fouled, the cause of the fouling must be determined before replacing the spark plugs.

Engine Mechanical

  1. Check engine mechanical for the following conditions: Check the compression. See «MECHANICAL INSPECTION»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-31l) in BASIC DIAGNOSTIC PROCEDURES - 3.1L CENTURY, GRAND PRIX & MALIBU article. Sticking or leaking valves. Worn camshaft lobes. Worn camshaft lobes. Valve timing. Bent push rods. Worn rocker arms. Broken valve springs. Excessive oil in combustion chamber. Leaking valve seals. Low cylinder compression.
  2. Check for incorrect engine parts, such as the camshaft, cylinder heads, pistons, etc.
  3. Diagnose mechanical condition of the engine. See appropriate article in ENGINES.

Additional Checks

  1. Check the exhaust system for possible restrictions: Check the exhaust system for damaged or collapsed pipes. Check the mufflers for heat distress or possible internal failure. Check for possible catalytic converter restrictions by testing the exhaust system back pressure. See «EXHAUST SYSTEM CHECK»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l__exhaust-system-check) under EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  2. An engine miss condition can be caused by Electromagnetic Interference (EMI) on the reference circuit. EMI can usually be detected by monitoring engine RPM with a scan tool. A sudden increase in RPM with little change in actual engine speed indicates EMI is present. If a condition exists, check the routing of secondary ignition wires, or high voltage components near the ignition control circuits.

A mild to severe ping, usually worse under acceleration. The engine makes sharp metallic knocks which change with amount of acceleration.

  1. Check the fuel system circuits for proper operation. See «FUEL PUMP ELECTRICAL CIRCUIT DIAGNOSIS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-31l__fuel-pump-electrical-circuit-diagnosis) under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  2. Check for low fuel pressure. See «FUEL SYSTEM DIAGNOSIS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-31l__fuel-system-diagnosis) under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  3. Check for faulty fuel injectors. See «FUEL INJECTOR BALANCE TEST WITH SPECIAL TOOL»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) , «FUEL INJECTOR BALANCE TEST WITH TECH 2»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) and «FUEL INJECTOR COIL TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) under FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  4. Check for fuel contamination. See «ALCOHOL/CONTAMINANTS-IN-FUEL DIAGNOSIS W/O SPECIAL TOOL»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) or «ALCOHOL/CONTAMINANTS-IN-FUEL DIAGNOSIS W/ SPECIAL TOOL»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) under FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  5. Check any items which may cause an engine to run rich, long term fuel trim is significantly in the negative range. See «DIAGNOSTIC AIDS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) for DTC P0172: FUEL TRIM SYSTEM RICH under DIAGNOSTIC TESTS under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  6. Check any items which may cause an engine to run lean, long term fuel trim is significantly in the positive range. See «DIAGNOSTIC AIDS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) for DTC P0171: FUEL TRIM SYSTEM LEAN under DIAGNOSTIC TESTS under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article.

Check the spark plugs for proper heat range and reach. See IGNITION SYSTEM SPECIFICATIONS in appropriate SERVICE & ADJUSTMENT SPECIFICATIONS article. Check for proper ignition voltage output using the following steps

  1. Attach Spark Tester (J 26792) to engine ground.
  2. Connect the spark plug end of the spark plug wire to the spark tester. Connect the other end of the spark plug wire to the coil being tested.
  3. Connect the spark plug end of the companion spark plug wire to ground. The companion spark plug wire is the wire attached to the corresponding coil tower.
  4. Crank the engine while observing the spark tester. A spark should be observed.
  5. Repeat steps 1 - 4 for each coil.

If spark is not present at the coils, check for the following conditions

  1. Coils - Cracks, carbon tracking/arcing, or a resistance value outside 5-8 k/ohms.
  2. Spark Plug Wires - Signs of arcing, cross firing, cracks, carbon tracking, plug boot damage, pinched, improper routing, or a resistance value outside 3000 ohms per foot (9868 ohms per meter). Spraying the secondary ignition wires with a light mist of water may help locate an intermittent condition. Ignition voltage arcs to ground when a secondary component is faulty.
  3. Defective Ignition Module - See «ELECTRONIC IGNITION SYSTEM DIAGNOSIS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l__electronic-ignition-system-diagnosis) under IGNITION SYSTEMS in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  4. Ignition System Wiring - Loose ignition module feed or ground connection, or damaged system wiring.

Remove spark plugs and check for the following conditions

  1. Fouled plugs.
  2. Cracks.
  3. Wear.
  4. Improper gap.
  5. Burned or damaged electrodes.
  6. Improper heat range or reach.

If spark plugs are gas or oil fouled, the cause of the fouling must be determined before replacing the spark plugs.

Engine Cooling System

Check for obvious overheating conditions

  1. Low engine coolant
  2. Restricted air flow to the radiator, or restricted water flow through the radiator.
  3. Inoperative electric cooling fan circuits.
  4. Correct coolant solution should be a 50/50 mix.
  1. Excessive oil in combustion chamber. Leaking valve seals.
  2. Low cylinder compression. Check the compression. See «MECHANICAL INSPECTION»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-31l) in BASIC DIAGNOSTIC PROCEDURES - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  3. Check for incorrect engine parts, such as cylinder heads, camshaft and valve train components, pistons, etc.
  4. Diagnose mechanical condition of the engine. See appropriate article in ENGINES.
  1. Check the Crankshaft Position (CKP) sensor "B" for an internal short.
  2. Check for proper Exhaust Gas Recirculation (EGR) system operation. See «DTC P0401: EGR FLOW INSUFFICIENT»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__dtc-p0401-egr-flow-insufficient) under DIAGNOSTIC TESTS in SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  3. Check the transaxle range switch input with the vehicle in Drive and the gear selector in Drive or Overdrive.
  4. Check the Torque Converter Clutch (TCC) operation. TCC applying too soon can cause the engine to spark knock.
  5. If the scan tool readings are normal and there are no engine mechanical faults, fill the fuel tank with a known quality gasoline that has a minimum octane reading of 87 and re-evaluate vehicle performance.

Fuel ignites in intake manifold or in exhaust system, making a loud popping noise.

Check the following

  1. Monitor the 24X sensor and the Camshaft Position (CMP) sensor signal present parameters on the scan tool. If both are not responding, test the sensor feed circuit. Both sensors use a separate feed circuit but are internally connected to power. Check all CKP sensor "A" and CMP sensor circuits for intermittents. See «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) .
  2. Monitor the 3X parameter on the scan tool. If the 3X is not responding, check the CKP sensor "B" and circuits for intermittents. Check the Ignition Control (IC) circuit, IC timing control circuit, low resolution engine speed signal circuit and the low reference circuit for intermittents. If these circuits become open, or shorted may not set a DTC immediately, but are capable of causing driveability complaints.
  3. Check the Mass Airflow (MAF) sensor conditions. Ensure that the MAF sensor honeycomb is not damaged.
  1. Check for low fuel pressure. See «FUEL SYSTEM DIAGNOSIS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-31l__fuel-system-diagnosis) under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  2. Check for fuel contamination. See «ALCOHOL/CONTAMINANTS-IN-FUEL DIAGNOSIS W/O SPECIAL TOOL»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) or «ALCOHOL/CONTAMINANTS-IN-FUEL DIAGNOSIS W/ SPECIAL TOOL»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) under FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  3. Ensure that each injector harness is connected to the correct injector/cylinder.

Check the spark plugs for proper heat range and reach. See IGNITION SYSTEM SPECIFICATIONS in appropriate SERVICE & ADJUSTMENT SPECIFICATIONS article. Check for proper ignition voltage output using the following steps

  1. Attach Spark Tester (J 26792) to engine ground.
  2. Connect the spark plug end of the spark plug wire to the spark tester. Connect the other end of the spark plug wire to the coil being tested.
  3. Connect the spark plug end of the companion spark plug wire to ground. The companion spark plug wire is the wire attached to the corresponding coil tower.
  4. Crank the engine while observing the spark tester. A spark should be observed.
  5. Repeat steps 1 - 4 for each coil.

If spark is not present at the coils, check for the following conditions

  1. Coils - Cracks, carbon tracking/arcing, or a resistance value outside 5-8 k/ohms.
  2. Spark Plug Wires - Signs of arcing, cross firing, cracks, carbon tracking, plug boot damage, pinched, improper routing, or a resistance value outside 3000 ohms per foot (9868 ohms per meter). Spraying the secondary ignition wires with a light mist of water may help locate an intermittent condition. Ignition voltage arcs to ground when a secondary component is faulty.
  3. Defective Ignition Module - See «ELECTRONIC IGNITION SYSTEM DIAGNOSIS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l__electronic-ignition-system-diagnosis) under IGNITION SYSTEMS in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  4. Ignition System Wiring - Loose ignition module feed or ground connection, or damaged system wiring.

Remove spark plugs and check for the following conditions

  1. Fouled plugs.
  2. Cracks.
  3. Wear.
  4. Improper gap.
  5. Burned or damaged electrodes.
  6. Improper heat range or reach.

If spark plugs are gas or oil fouled, the cause of the fouling must be determined before replacing the spark plugs.

  1. Check engine mechanical for the following conditions: Check the compression. See «MECHANICAL INSPECTION»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-31l) in BASIC DIAGNOSTIC PROCEDURES - 3.1L CENTURY, GRAND PRIX & MALIBU article. Sticking or leaking valves. Worn camshaft lobes. Worn camshaft lobes. Valve timing. Bent push rods. Worn rocker arms. Broken valve springs. Excessive oil in combustion chamber. Leaking valve seals. Low cylinder compression.
  2. Check for incorrect engine parts, such as the camshaft, cylinder heads, pistons, etc.
  3. Diagnose mechanical condition of the engine. See appropriate article in ENGINES.
  1. Check intake and exhaust manifolds for casting flash. See «EXHAUST SYSTEM CHECK»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l__exhaust-system-check) under EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  2. Check the Torque Converter Clutch (TCC) operation. See appropriate DIAGNOSIS article in TRANSMISSIONS.
  3. Check the exhaust system for possible restriction: See «EXHAUST RESTRICTION»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l__restricted-exhaust) under EXHAUST SYSTEM CHECK under EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article. Check the exhaust system for damaged or collapsed pipes. Check the mufflers for heat distress or possible internal failure. Check for possible catalytic converter restrictions by testing the exhaust system back pressure.

Engine continues to run after ignition is turned off but runs very rough. If engine runs smoothly, check ignition switch and adjustment.

  1. Check the fuel system circuits for proper operation. See «FUEL PUMP ELECTRICAL CIRCUIT DIAGNOSIS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-31l__fuel-pump-electrical-circuit-diagnosis) under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  2. Check for low fuel pressure. See «FUEL SYSTEM DIAGNOSIS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-31l__fuel-system-diagnosis) under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  3. Check for faulty fuel injectors. See «FUEL INJECTOR BALANCE TEST WITH SPECIAL TOOL»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) , «FUEL INJECTOR BALANCE TEST WITH TECH 2»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) and «FUEL INJECTOR COIL TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) under FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  4. Check for fuel contamination. See «ALCOHOL/CONTAMINANTS-IN-FUEL DIAGNOSIS W/O SPECIAL TOOL»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) or «ALCOHOL/CONTAMINANTS-IN-FUEL DIAGNOSIS W/ SPECIAL TOOL»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) under FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  5. Check for fuel in the pressure regulator vacuum hose.
  6. Ensure that each injector harness is connected to the correct injector/cylinder.

Check for short between battery positive voltage and any of the ignition feed circuits.

Engine cranks okay, but does not start for a long time. Engine eventually starts, and may stall immediately or run okay.

  1. Check Engine Coolant Temperature (ECT) sensor for being shifted in value. Connect a scan tool and compare ECT with Intake Air Temperature (IAT) on a cold engine. The ECT and IAT should be within 5°F of each other. Check the resistance of the ECT sensor if the temperature is out of range with the IAT sensor. See «TEMPERATURE VS. RESISTANCE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l) table. If the ECT sensor resistance is not within specification, see «DTC P0113: INTAKE AIR TEMPERATURE SENSOR CIRCUIT - HIGH VOLTAGE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__dtc-p0113-intake-air-temperature-sensor) under DIAGNOSTIC TESTS in SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article. On Malibu, also see «DTC P0117: ENGINE COOLANT TEMPERATURE SENSOR CIRCUIT - LOW VOLTAGE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__dtc-p0117-engine-coolant-temperature-sensor) under DIAGNOSTIC TESTS in SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  2. Monitor the 24X crank sensor and Camshaft Position (CMP) sensor signal present parameters on a scan tool. If both are not responding, test the sensor feed circuit. Both sensors use a separate feed circuit but are internally connected to power. Check all CKP sensor "A" and CMP sensor circuits for intermittents. See «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) .
  3. Monitor the 3X crank sensor parameter on the scan tool. If the 3X crank sensor parameter is not responding, check the CKP sensor and circuits for intermittents. Check the Ignition Control (IC) circuit, IC timing control circuit, low resolution engine speed signal circuit and the low reference circuit for intermittents. If these circuits become open, or shorted, they may not set a DTC immediately, but are capable of causing driveability complaints. See «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) .
  4. Check the Mass Airflow (MAF) sensor for proper installation and conditions. A MAF sensor with a damaged honeycomb may cause a hard start. Check the air intake ducts for being collapsed, damaged areas, looseness, improper installation, or leaking, especially between the MAF sensor and the throttle body.
  5. Using a scan tool, test the Idle Air Control (IAC) operation. Command the engine RPM to 1500 RPM and back to the starting RPM. If the engine RPM does not change when commanded, diagnose the IAC system. See «DTC P0506: IDLE SPEED LOW»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__dtc-p0506-idle-speed-low) and «DTC P0507: IDLE SPEED HIGH»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__dtc-p0507-idle-speed-high) under DIAGNOSTIC TESTS in SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  6. Check the Exhaust Gas Recirculation (EGR) system for proper sealing/connections and operation. See «EXHAUST GAS RECIRCULATION»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l__exhaust-gas-recirculation) under EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
°F (°C)Ohms
302 (150)47
284 (140)60
266 (130)77
248 (120)100
230 (110)132
212 (100)177
194 (90)241
176 (80)332
158 (70)467
140 (60)667
122 (50)973
113 (45)1188
104 (40)1459
95 (35)1802
86 (30)2238
77 (25)2796
68 (20)3520
59 (15)4450
50 (10)5670
41 (5)7280
32 (0)9420
23 (-5)12,300
14 (-10)16,180
5 (-15)21,450
4 (-20)28,680
22 (-30)52,700
40 (-40)100,700

TEMPERATURE VS. RESISTANCE

  1. Check the fuel system circuits for proper operation. See «FUEL PUMP ELECTRICAL CIRCUIT DIAGNOSIS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-31l__fuel-pump-electrical-circuit-diagnosis) under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  2. Check for low fuel pressure. See «FUEL SYSTEM DIAGNOSIS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-31l__fuel-system-diagnosis) under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  3. Check for faulty fuel injectors. See «FUEL INJECTOR BALANCE TEST WITH SPECIAL TOOL»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) , «FUEL INJECTOR BALANCE TEST WITH TECH 2»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) and «FUEL INJECTOR COIL TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) under FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  4. Check for fuel contamination. See «ALCOHOL/CONTAMINANTS-IN-FUEL DIAGNOSIS W/O SPECIAL TOOL»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) or «ALCOHOL/CONTAMINANTS-IN-FUEL DIAGNOSIS W/ SPECIAL TOOL»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) under FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.

Check the spark plugs for proper heat range and reach. See IGNITION SYSTEM SPECIFICATIONS in appropriate SERVICE & ADJUSTMENT SPECIFICATIONS article. Check for proper ignition voltage output using the following steps

  1. Attach Spark Tester (J 26792) to engine ground.
  2. Connect the spark plug end of the spark plug wire to the spark tester. Connect the other end of the spark plug wire to the coil being tested.
  3. Connect the spark plug end of the companion spark plug wire to ground. The companion spark plug wire is the wire attached to the corresponding coil tower.
  4. Crank the engine while observing the spark tester. A spark should be observed.
  5. Repeat steps 1 - 4 for each coil.

If spark is not present at the coils, check for the following conditions

  1. Coils - Cracks, carbon tracking/arcing, or a resistance value outside 5-8 k/ohms.
  2. Spark Plug Wires - Signs of arcing, cross firing, cracks, carbon tracking, plug boot damage, pinched, improper routing, or a resistance value outside 3000 ohms per foot (9868 ohms per meter). Spraying the secondary ignition wires with a light mist of water may help locate an intermittent condition. Ignition voltage arcs to ground when a secondary component is faulty.
  3. Defective Ignition Module - See «ELECTRONIC IGNITION SYSTEM DIAGNOSIS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l__electronic-ignition-system-diagnosis) under IGNITION SYSTEMS in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  4. Ignition System Wiring - Loose ignition module feed or ground connection, or damaged system wiring.

Remove spark plugs and check for the following conditions

  1. Fouled plugs.
  2. Cracks.
  3. Wear.
  4. Improper gap.
  5. Burned or damaged electrodes.
  6. Improper heat range or reach.

If spark plugs are gas or oil fouled, the cause of the fouling must be determined before replacing the spark plugs.

  1. Excessive oil in combustion chamber. Leaking valve seals.
  2. Low cylinder compression. Check the compression. See «MECHANICAL INSPECTION»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-31l) in BASIC DIAGNOSTIC PROCEDURES - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  3. Check for incorrect engine parts, such as cylinder heads, camshaft and valve train components, pistons, etc.
  4. Diagnose mechanical condition of the engine. See appropriate article in ENGINES.

Momentary lack of response when accelerator is pushed down. Condition occurs at all vehicle speeds or usually occurs when taking off from a stop. If severe enough, may cause engine to stall.

  1. Monitor the Heated Oxygen Sensors (HO2S). The HO2S should respond quickly to different throttle positions. If not, check the HO2S for silicone or other contaminants from fuel or use of improper RTV sealant. The sensors may have a White powdery coating. Silicone contamination causes a high but false HO2S signal voltage, rich exhaust indication. The Powertrain Control Module (PCM) reduces the amount of fuel delivered to the engine, causing a severe driveability condition.
  2. Monitor the 24X crank sensor and the Camshaft Position (CMP) sensor signal present parameters on the scan tool. If both are not responding, test the sensor feed circuit. Both sensors use a separate feed circuit but are internally connected to power. Check all Crankshaft Position (CKP) "A" and CMP sensor circuits for intermittents.
  3. Check the CKP sensor "B" for an internal short. See «ELECTRONIC IGNITION SYSTEM DIAGNOSIS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l__electronic-ignition-system-diagnosis) under IGNITION SYSTEMS in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  4. Check the Throttle Position (TP) sensor and related wiring.
  5. Check the Mass Airflow (MAF) sensor and related wiring. Check the air intake ducts for being collapsed, damaged areas, looseness, improper installation, or leaking especially between the MAF sensor and the throttle body.
  6. Check the Exhaust Gas Recirculation (EGR) system for proper operation. See «EXHAUST GAS RECIRCULATION»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l__exhaust-gas-recirculation) under EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  1. Check the fuel system circuits for proper operation. See «FUEL PUMP ELECTRICAL CIRCUIT DIAGNOSIS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-31l__fuel-pump-electrical-circuit-diagnosis) under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  2. Check for low fuel pressure. See «FUEL SYSTEM DIAGNOSIS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-31l__fuel-system-diagnosis) under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  3. Check for faulty fuel injectors. See «FUEL INJECTOR BALANCE TEST WITH SPECIAL TOOL»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) , «FUEL INJECTOR BALANCE TEST WITH TECH 2»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) and «FUEL INJECTOR COIL TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) under FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  4. Check for fuel contamination. See «ALCOHOL/CONTAMINANTS-IN-FUEL DIAGNOSIS W/O SPECIAL TOOL»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) or «ALCOHOL/CONTAMINANTS-IN-FUEL DIAGNOSIS W/ SPECIAL TOOL»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) under FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  5. Check any items which may cause an engine to run rich, long term fuel trim is significantly in the negative range. See «DIAGNOSTIC AIDS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) for DTC P0172: FUEL TRIM SYSTEM RICH under DIAGNOSTIC TESTS in SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  6. Check any items which may cause an engine to run lean, long term fuel trim is significantly in the positive range. See «DIAGNOSTIC AIDS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) for DTC P0171: FUEL TRIM SYSTEM LEAN under DIAGNOSTIC TESTS in SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article.

Check for proper ignition voltage output using the following steps

  1. Attach Spark Tester (J 26792) to engine ground.
  2. Connect the spark plug end of the spark plug wire to the spark tester. Connect the other end of the spark plug wire to the coil being tested.
  3. Connect the spark plug end of the companion spark plug wire to ground. The companion spark plug wire is the wire attached to the corresponding coil tower.
  4. Crank the engine while observing the spark tester. A spark should be observed.
  5. Repeat steps 1 - 4 for each coil.

If spark is not present at the coils, check for the following conditions

  1. Coils - Cracks, carbon tracking/arcing, or a resistance value outside 5-8 k/ohms.
  2. Spark Plug Wires - Signs of arcing, cross firing, cracks, carbon tracking, plug boot damage, pinched, improper routing, or a resistance value outside 3000 ohms per foot (9868 ohms per meter). Spraying the secondary ignition wires with a light mist of water may help locate an intermittent condition. Ignition voltage arcs to ground when a secondary component is faulty.
  3. Defective Ignition Module - See «ELECTRONIC IGNITION SYSTEM DIAGNOSIS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l__electronic-ignition-system-diagnosis) under IGNITION SYSTEMS in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  4. Ignition System Wiring - Loose ignition module feed or ground connection, or damaged system wiring.

Remove spark plugs and check for the following conditions

  1. Fouled plugs.
  2. Cracks.
  3. Wear.
  4. Improper gap.
  5. Burned or damaged electrodes.
  6. Improper heat range or reach.

If spark plugs are gas or oil fouled, the cause of the fouling must be determined before replacing the spark plugs.

Engine delivers less than expected power. Little or no increase in speed when the accelerator pedal is pushed down part way.

  1. Check the fuel system circuits for proper operation. See «FUEL PUMP ELECTRICAL CIRCUIT DIAGNOSIS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-31l__fuel-pump-electrical-circuit-diagnosis) under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  2. Check for low fuel pressure. See «FUEL SYSTEM DIAGNOSIS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-31l__fuel-system-diagnosis) under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  3. Check for faulty fuel injectors. See «FUEL INJECTOR BALANCE TEST WITH SPECIAL TOOL»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) , «FUEL INJECTOR BALANCE TEST WITH TECH 2»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) and «FUEL INJECTOR COIL TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) under FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  4. Check for fuel contamination. See «ALCOHOL/CONTAMINANTS-IN-FUEL DIAGNOSIS W/O SPECIAL TOOL»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) or «ALCOHOL/CONTAMINANTS-IN-FUEL DIAGNOSIS W/ SPECIAL TOOL»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) under FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  5. Check any items which may cause an engine to run rich, long term fuel trim is significantly in the negative range. See «DIAGNOSTIC AIDS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) for DTC P0172: FUEL TRIM SYSTEM RICH under DIAGNOSTIC TESTS in SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  6. Check any items which may cause an engine to run lean, long term fuel trim is significantly in the positive range. See «DIAGNOSTIC AIDS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) for DTC P0171: FUEL TRIM SYSTEM LEAN under DIAGNOSTIC TESTS in SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  1. Check the Crankshaft Position (CKP) sensor "B" for an internal short. See «ELECTRONIC IGNITION SYSTEM DIAGNOSIS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l__electronic-ignition-system-diagnosis) under IGNITION SYSTEMS in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  2. Using a scan tool, monitor Knock Sensor (KS) system for excessive spark retard activity. See «KNOCK SENSOR»(/buick/century/vi-1997-2005/remont/theory-operation/#engine-controls-theory-operation__knock-sensor) under INPUT DEVICES in THEORY & OPERATION - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  3. If knock retard is above 10-12 degrees, disconnect the KS, and ground the sensor harness connector. Monitor knock retard on the scan tool, there should be no knock retard present, if knock retard is still present, replace the Powertrain Control Module (PCM).
  4. Check the Exhaust Gas Recirculation (EGR) system for proper operation. See «EXHAUST GAS RECIRCULATION»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l__exhaust-gas-recirculation) under EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  5. Check the air intake ducts for being collapsed, damaged areas, looseness, improper installation, or leaking especially between the Mass Airflow (MAF) sensor and the throttle body.

Check for proper ignition voltage output using the following steps

  1. Attach Spark Tester (J 26792) to engine ground.
  2. Connect the spark plug end of the spark plug wire to the spark tester. Connect the other end of the spark plug wire to the coil being tested.
  3. Connect the spark plug end of the companion spark plug wire to ground. The companion spark plug wire is the wire attached to the corresponding coil tower.
  4. Crank the engine while observing the spark tester. A spark should be observed.
  5. Repeat steps 1 - 4 for each coil.

If spark is not present at the coils, check for the following conditions

  1. Coils - Cracks, carbon tracking/arcing, or a resistance value outside 5-8 k/ohms.
  2. Spark Plug Wires - Signs of arcing, cross firing, cracks, carbon tracking, plug boot damage, pinched, improper routing, or a resistance value outside 3000 ohms per foot (9868 ohms per meter). Spraying the secondary ignition wires with a light mist of water may help locate an intermittent condition. Ignition voltage arcs to ground when a secondary component is faulty.
  3. Defective Ignition Module - See «ELECTRONIC IGNITION SYSTEM DIAGNOSIS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l__electronic-ignition-system-diagnosis) under IGNITION SYSTEMS in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  4. Ignition System Wiring - Loose ignition module feed or ground connection, or damaged system wiring.

Remove spark plugs and check for the following conditions

  1. Fouled plugs.
  2. Cracks.
  3. Wear.
  4. Improper gap.
  5. Burned or damaged electrodes.
  6. Improper heat range or reach.

If spark plugs are gas or oil fouled, the cause of the fouling must be determined before replacing the spark plugs.

  1. Excessive oil in combustion chamber. Leaking valve seals.
  2. Low cylinder compression. Check the compression. See «MECHANICAL INSPECTION»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-31l) in BASIC DIAGNOSTIC PROCEDURES - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  3. Check for incorrect engine parts, such as cylinder heads, camshaft and valve train components, pistons, etc.
  4. Diagnose mechanical condition of the engine. See appropriate article in ENGINES.

Check the exhaust system for any possible restrictions. See EXHAUST RESTRICTION under EXHAUST SYSTEM CHECK under EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.

  1. Check exhaust system for damaged or collapsed pipes.
  2. Check mufflers for heat distress or possible internal failure.
  3. For possible plugged catalytic converter.
  4. Check for proper Torque Converter Clutch (TCC) operation. Check the Torque Converter Clutch (TCC) operation. See appropriate DIAGNOSIS article in TRANSMISSIONS.

Fuel economy, as measured by an actual road test is noticeably lower than expected. Also, the economy is noticeably lower than the economy was on this vehicle at one time, as previously shown by an actual road test.

Preliminary

Observe the owners driving habits. Is the A/C ON full time, defroster mode ON? Are tires at correct pressure? Are tires and wheels the correct size? Are excessively heavy loads being carried? Is acceleration too much, too often?

  1. Check the fuel system circuits for proper operation. See «FUEL PUMP ELECTRICAL CIRCUIT DIAGNOSIS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-31l__fuel-pump-electrical-circuit-diagnosis) under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  2. Check for low fuel pressure. See «FUEL SYSTEM DIAGNOSIS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-31l__fuel-system-diagnosis) under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  3. Check for faulty fuel injectors. See «FUEL INJECTOR BALANCE TEST WITH SPECIAL TOOL»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) , «FUEL INJECTOR BALANCE TEST WITH TECH 2»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) and «FUEL INJECTOR COIL TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) under FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  4. Check for fuel contamination. See «ALCOHOL/CONTAMINANTS-IN-FUEL DIAGNOSIS W/O SPECIAL TOOL»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) or «ALCOHOL/CONTAMINANTS-IN-FUEL DIAGNOSIS W/ SPECIAL TOOL»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) under FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  5. Ensure that each injector harness is connected to the correct injector/cylinder.
  6. Check for fuel in the pressure regulator vacuum hose.
  1. Observe the 24X crank sensor and Camshaft Position (CMP) sensor signal present parameters on the scan tool. If both are not responding, check the sensor feed circuit. Both sensors use a common feed circuit.
  2. Check the air intake system and crankcase for air leaks. Check the air intake ducts for being collapsed, damaged areas, looseness, improper installation, or leaking, especially between the Mass Airflow (MAF) sensor and the throttle body.
  3. Check for proper operation of the speedometer. See appropriate ANALOG INSTRUMENT PANELS article in ACCESSORIES & EQUIPMENT.

Check for proper ignition voltage output using the following steps

  1. Attach Spark Tester (J 26792) to engine ground.
  2. Connect the spark plug end of the spark plug wire to the spark tester. Connect the other end of the spark plug wire to the coil being tested.
  3. Connect the spark plug end of the companion spark plug wire to ground. The companion spark plug wire is the wire attached to the corresponding coil tower.
  4. Crank the engine while observing the spark tester. A spark should be observed.
  5. Repeat steps 1 - 4 for each coil.

If spark is not present at the coils, check for the following conditions

  1. Coils - Cracks, carbon tracking/arcing, or a resistance value outside 5-8 k/ohms.
  2. Spark Plug Wires - Signs of arcing, cross firing, cracks, carbon tracking, plug boot damage, pinched, improper routing, or a resistance value outside 3000 ohms per foot (9868 ohms per meter). Spraying the secondary ignition wires with a light mist of water may help locate an intermittent condition. Ignition voltage arcs to ground when a secondary component is faulty.
  3. Defective Ignition Module - See «ELECTRONIC IGNITION SYSTEM DIAGNOSIS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l__electronic-ignition-system-diagnosis) under IGNITION SYSTEMS in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  4. Ignition System Wiring - Loose ignition module feed or ground connection, or damaged system wiring.

Remove spark plugs and check for the following conditions

  1. Fouled plugs.
  2. Cracks.
  3. Wear.
  4. Improper gap.
  5. Burned or damaged electrodes.
  6. Improper heat range or reach.

If spark plugs are gas or oil fouled, the cause of the fouling must be determined before replacing the spark plugs.

  1. Check the engine coolant level for correct level.
  2. Check for incorrect or faulty engine thermostat.
  1. Check the engine for the following conditions: Check the compression. Check the compression. See «MECHANICAL INSPECTION»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-31l) in BASIC DIAGNOSTIC PROCEDURES - 3.1L CENTURY, GRAND PRIX & MALIBU article. Sticking or leaking valves. Worn camshaft lobes. Valve timing. Bent push rods. Worn rocker arms. Broken valve springs. Excessive oil in combustion chamber. Leaking valve seals.
  2. Check for incorrect engine parts, such as the camshaft, cylinder heads, pistons, etc.
  3. Diagnose mechanical condition of the engine. See appropriate article in ENGINES.

Check the exhaust system for any possible restrictions.

  1. See «EXHAUST RESTRICTION»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l__restricted-exhaust) under EXHAUST SYSTEM CHECK under EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  2. Check exhaust system for damaged or collapsed pipes.
  3. Check mufflers for heat distress or possible internal failure.
  4. For possible plugged catalytic converter.
  5. Check for proper Torque Converter Clutch (TCC) operation. Check the Torque Converter Clutch (TCC) operation. See appropriate DIAGNOSIS article in TRANSMISSIONS.

During the fueling process a continual, occasional or no fuel nozzle shut-off condition has occurred.

Occasional Shut-Off Of The Fuel Dispensing Nozzle

Check the following

  1. Fill limiter vent valve stuck closed.
  2. EVAP canister restricted.
  3. EVAP vent valve stuck closed.
  4. Restricted vapor lines.
  5. High Reid vapor pressure or high fuel temperature.
  6. Fuel filler hose is pinched or kinked.
  7. Ignition switch in RUN position (EVAP vent valve closed).

Continual Shut-Off Of The Fuel Dispensing Nozzle

  1. Fill limiter vent valve stuck closed.
  2. EVAP canister blocked.
  3. EVAP vent valve stuck closed.
  4. Restricted or pinched EVAP vapor lines.
  5. Blocked fuel filler hose/pipe or fuel fill check valve.

No Nozzle Shut-Off/Over Fill

  1. Pressure relief valve is stuck open or leaking.
  2. Fill limiter vent valve is stuck open or leaking.

Engine runs unevenly at idle. If severe enough, vehicle will shake. Idle may vary in RPM. Either problem may cause stalling. Engine idles at incorrect RPM.

  1. Check the fuel system circuits for proper operation. See «FUEL PUMP ELECTRICAL CIRCUIT DIAGNOSIS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-31l__fuel-pump-electrical-circuit-diagnosis) under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  2. Check for low fuel pressure. See «FUEL SYSTEM DIAGNOSIS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-31l__fuel-system-diagnosis) under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  3. Check for faulty fuel injectors. See «FUEL INJECTOR BALANCE TEST WITH SPECIAL TOOL»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) , «FUEL INJECTOR BALANCE TEST WITH TECH 2»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) and «FUEL INJECTOR COIL TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) under FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  4. Check for fuel contamination. See «ALCOHOL/CONTAMINANTS-IN-FUEL DIAGNOSIS W/O SPECIAL TOOL»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) or «ALCOHOL/CONTAMINANTS-IN-FUEL DIAGNOSIS W/ SPECIAL TOOL»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) under FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  5. Check any items which may cause an engine to run rich, long term fuel trim is significantly in the negative range. See «DIAGNOSTIC AIDS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) for DTC P0172: FUEL TRIM SYSTEM RICH under DIAGNOSTIC TESTS in SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  6. Check any items which may cause an engine to run lean, long term fuel trim is significantly in the positive range. See «DIAGNOSTIC AIDS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) for DTC P0171: FUEL TRIM SYSTEM LEAN under DIAGNOSTIC TESTS in SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  1. Check for conditions which cause an incorrect idle speed: Throttle body tampering, excessive deposits, or damage. Restricted air intake system. Large vacuum leak.
  2. Check the air intake ducts for being collapsed, damaged areas, looseness, improper installation, or leaking especially between the Mass Airflow (MAF) sensor and the throttle body.
  3. Check crankcase ventilation valve for proper operation.
  4. Check the Throttle Position (TP) sensor and related wiring. See «DTC P0123: THROTTLE POSITION SENSOR CIRCUIT - HIGH VOLTAGE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__dtc-p0123-throttle-position-sensor-circuit) under DIAGNOSTIC TESTS in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  5. Monitor the 24X crank sensor and the Camshaft Position (CMP) sensor signal present parameter on the scan tool. If both are not responding, test the sensor feed circuit. Both sensors use a separate feed circuit but are internally connected to power. Check all CKP sensor "A" and CMP sensor circuits for intermittents. See «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) .
  6. Monitor the 3X parameter on the scan tool. If the 3X is not responding, check the CKP sensor "B" and circuits for intermittents. Check the Ignition Control (IC) circuit, IC timing control circuit, low resolution engine speed signal circuit and the low reference circuit for intermittents. If these circuits become open, or shorted may not set a DTC immediately, but are capable of causing driveability complaints. See «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) .
  7. Check the Exhaust Gas Recirculation (EGR) system for proper operation. See «EXHAUST GAS RECIRCULATION»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l__exhaust-gas-recirculation) under EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  8. Check the transaxle range switch input with the vehicle in Drive and the gear selector in Drive or Overdrive.

Check for proper ignition voltage output using the following steps

  1. Attach Spark Tester (J 26792) to engine ground.
  2. Connect the spark plug end of the spark plug wire to the spark tester. Connect the other end of the spark plug wire to the coil being tested.
  3. Connect the spark plug end of the companion spark plug wire to ground. The companion spark plug wire is the wire attached to the corresponding coil tower.
  4. Crank the engine while observing the spark tester. A spark should be observed.
  5. Repeat steps 1 - 4 for each coil.

If spark is not present at the coils, check for the following conditions

  1. Coils - Cracks, carbon tracking/arcing, or a resistance value outside 5-8 k/ohms.
  2. Spark Plug Wires - Signs of arcing, cross firing, cracks, carbon tracking, plug boot damage, pinched, improper routing, or a resistance value outside 3000 ohms per foot (9868 ohms per meter). Spraying the secondary ignition wires with a light mist of water may help locate an intermittent condition. Ignition voltage arcs to ground when a secondary component is faulty.
  3. Defective Ignition Module - See «ELECTRONIC IGNITION SYSTEM DIAGNOSIS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l__electronic-ignition-system-diagnosis) under IGNITION SYSTEMS in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  4. Ignition System Wiring - Loose ignition module feed or ground connection, or damaged system wiring.

Remove spark plugs and check for the following conditions

  1. Fouled plugs.
  2. Cracks.
  3. Wear.
  4. Improper gap.
  5. Burned or damaged electrodes.
  6. Improper heat range or reach.

If spark plugs are gas or oil fouled, the cause of the fouling must be determined before replacing the spark plugs.

  1. Check the engine for the following conditions: Check the compression. Check the compression. See «MECHANICAL INSPECTION»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-31l) in BASIC DIAGNOSTIC PROCEDURES - 3.1L CENTURY, GRAND PRIX & MALIBU article. Sticking or leaking valves. Worn camshaft lobes. Valve timing. Bent push rods. Worn rocker arms. Broken valve springs. Excessive oil in combustion chamber. Leaking valve seals.
  2. Check for incorrect engine parts, such as the camshaft, cylinder heads, pistons, etc.
  3. Diagnose mechanical condition of the engine. See appropriate article in ENGINES.

Check the exhaust system for possible restrictions

  1. See «EXHAUST RESTRICTION»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l__restricted-exhaust) under EXHAUST SYSTEM CHECK under EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  2. Check the exhaust system for damaged or collapsed pipes.
  3. Check the mufflers for heat distress or possible internal failure.
  4. Check for possible catalytic converter restrictions by testing the exhaust system back pressure.
  5. An engine miss condition can be caused by Electromagnetic Interference (EMI) on the reference circuit. EMI can usually be detected by monitoring engine RPM with a scan tool. A sudden increase in RPM with little change in actual engine RPM change, indicates EMI is present. If a condition exists, check the routing of secondary ignition wires, high voltage components, e.g. near ignition control circuits.
  6. Check for intake and exhaust manifold passages for casting flash.

Engine power varies under steady throttle or cruise. Vehicle speeds up and slows down without changing position of accelerator pedal.

  1. Monitor the Heated Oxygen Sensors (HO2S). The HO2S should respond quickly to different throttle positions. If not, check the HO2S for silicone or other contaminants from fuel or use of improper RTV sealant. The sensors may have a White powdery coating. Silicone contamination causes a high but false HO2S signal voltage, rich exhaust indication. The Powertrain Control Module (PCM) reduces the amount of fuel delivered to the engine, causing a severe driveability problem.
  2. Check MAF sensor and related wiring.
  3. Check the air intake ducts for being collapsed, damaged areas, looseness, improper installation, or leaking especially between the Mass Airflow (MAF) sensor and the throttle body.
  4. Monitor the 24X crank sensor and CMP sensor signal present parameters on the scan tool. If both are not responding, test the sensor feed circuit. Both sensors use a separate feed circuit but are internally connected to power. Check all CKP sensor "A" and CMP sensor circuits for intermittents. See «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) .
  5. Monitor the 3X crank sensor parameter on the scan tool. If the 3X crank sensor parameter is not responding, check the CKP sensor "B" and circuits for intermittents. Check the Ignition Control (IC) circuit, IC timing control circuit, low resolution engine speed signal circuit and the low reference circuit for intermittents. If these circuits become open, or shorted may not set a DTC immediately, but are capable of causing driveability complaints. See «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) .
  6. Check the Exhaust Gas Recirculation (EGR) system for proper operation. See «EXHAUST GAS RECIRCULATION»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l__exhaust-gas-recirculation) under EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  1. Check the fuel pressure. See «FUEL SYSTEM DIAGNOSIS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-31l__fuel-system-diagnosis) under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  2. Check for fuel contamination. See «ALCOHOL/CONTAMINANTS-IN-FUEL DIAGNOSIS W/O SPECIAL TOOL»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) or «ALCOHOL/CONTAMINANTS-IN-FUEL DIAGNOSIS W/ SPECIAL TOOL»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) under FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  3. Ensure that each injector harness is connected to the correct injector/cylinder.
  4. Check any items which may cause an engine to run rich, long term fuel trim is significantly in the negative range. See «DIAGNOSTIC AIDS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) for DTC P0172: FUEL TRIM SYSTEM RICH under DIAGNOSTIC TESTS in SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  5. Check any items which may cause an engine to run lean, long term fuel trim is significantly in the positive range. See «DIAGNOSTIC AIDS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) for DTC P0171: FUEL TRIM SYSTEM LEAN under DIAGNOSTIC TESTS in SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article.

Check for proper ignition voltage output using the following steps

  1. Attach Spark Tester (J 26792) to engine ground.
  2. Connect the spark plug end of the spark plug wire to the spark tester. Connect the other end of the spark plug wire to the coil being tested.
  3. Connect the spark plug end of the companion spark plug wire to ground. The companion spark plug wire is the wire attached to the corresponding coil tower.
  4. Crank the engine while observing the spark tester. A spark should be observed.
  5. Repeat steps 1 - 4 for each coil.

If spark is not present at the coils, check for the following conditions

  1. Coils - Cracks, carbon tracking/arcing, or a resistance value outside 5-8 k/ohms.
  2. Spark Plug Wires - Signs of arcing, cross firing, cracks, carbon tracking, plug boot damage, pinched, improper routing, or a resistance value outside 3000 ohms per foot (9868 ohms per meter). Spraying the secondary ignition wires with a light mist of water may help locate an intermittent condition. Ignition voltage arcs to ground when a secondary component is faulty.
  3. Defective Ignition Module - See «ELECTRONIC IGNITION SYSTEM DIAGNOSIS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l__electronic-ignition-system-diagnosis) under IGNITION SYSTEMS in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  4. Ignition System Wiring - Loose ignition module feed or ground connection, or damaged system wiring.

Remove spark plugs and check for the following conditions

  1. Fouled plugs.
  2. Cracks.
  3. Wear.
  4. Improper gap.
  5. Burned or damaged electrodes.
  6. Improper heat range or reach.

If spark plugs are gas or oil fouled, the cause of the fouling must be determined before replacing the spark plugs.

  1. See «EXHAUST RESTRICTION»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l__restricted-exhaust) under EXHAUST SYSTEM CHECK under EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  2. Check exhaust system for damaged or collapsed pipes.
  3. Check mufflers for heat distress or possible internal failure.
  4. For possible plugged catalytic converter.
  5. Check for proper Torque Converter Clutch (TCC) operation. Check the Torque Converter Clutch (TCC) operation. See appropriate DIAGNOSIS article in TRANSMISSIONS.

INTERMITTENTS

CAUTIONWhen battery is disconnected, vehicle computer and memory systems may lose memory data. Driveability problems may exist until computer systems have completed a relearn cycle. See COMPUTER RELEARN PROCEDURES article in GENERAL INFORMATION before disconnecting battery.

Perform the Diagnostic System Check - Engine Controls before starting. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article.

Definition

The condition is not currently present but is indicated in DTC History. Or, there is a customer complaint, but the symptom can not currently be duplicated, if the condition is not DTC related.

Harness Or Connector Intermittents

Many intermittent open or shorted circuits come and go with harness/connector movement caused by vibration, engine torque, bumps/rough pavement, etc. Check for this type of condition by performing the applicable procedure from the following list

  1. Move related connectors and wiring while monitoring the appropriate scan tool data.
  2. Move related connectors and wiring with the component commanded ON and OFF, with the scan tool. Observe the component operation.
  3. With the engine running, move related connectors and wiring while monitoring engine operation.

If harness or connector movement affects the data displayed, component/system operation, or engine operation, check and repair the harness/connections as necessary. See ELECTRICAL CONNECTIONS OR WIRING .

Electrical Connections Or Wiring

  1. Poor electrical connections/terminal tension or wiring conditions cause most intermittents. Perform a careful inspection of the suspected circuit for the following: Check for poor mating of the connector halves, or terminals not fully seated in the connector body (backed-out). Check for improperly formed or damaged terminals. Check for poor terminal tension. Check for poor terminal to wire connections including terminals crimped over insulation. This requires removing the terminal from the connector body. Check for corrosion/water intrusion. Pierced or damaged insulation can allow moisture to enter the wiring. The conductor can corrode inside the insulation, with little visible evidence. Look for swollen and stiff sections of wire in the suspect circuits. Check for wires that are broken inside the insulation. Check the harness for pinched, cut or rubbed through wiring. Ensure that the wiring does not come in contact with hot exhaust components.
  2. Repair the condition as necessary.

Control Module Power & Grounds & Component Power & Grounds

Poor power or ground connections can cause widely varying symptoms.

  1. Check all control module power circuits. Many vehicles have multiple circuits supplying power to the control module. Other components in the system may have separate power circuits that may also need to be tested. Check connections at the module or component connectors, fuses, and any intermediate connections between the power source and the module or component. A test light or a Digital Multimeter (DMM) may indicate that voltage is present, but neither tests the ability of a circuit to carry sufficient current. Ensure that the circuit can carry the current necessary to operate the component. See POWER DISTRIBUTION article in appropriate SYSTEM WIRING DIAGRAMS article in ELECTRICAL.
  2. Check all control module ground and system ground circuits. The control module may have multiple ground circuits. Other components in the system may have separate grounds that may also need to be tested. Check grounds for clean and tight connections at the grounding point. Check the connections at the component and in splice packs, where applicable. Ensure that the circuit can carry the current necessary to operate the component. See GROUND DISTRIBUTION article in appropriate SYSTEM WIRING DIAGRAMS article in ELECTRICAL.

Temperature Sensitivity

  1. An intermittent condition may occur when a component or connection reaches normal operating temperature. The condition may occur only when the component or connection is cold, or only when the connection is hot.
  2. The following data may help to diagnose this type of intermittent condition: Freeze Frame/Failure Records. Scan tool snapshot. Vehicle data recorder.
  3. If the intermittent is related to heat, review the following data: High ambient temperatures. Underhood or engine generated heat. Circuit generated heat due to a poor connection, or high electrical load. Higher than normal load conditions, such as towing.
  4. If the intermittent is related to cold, review the following data: Low ambient temperatures. In extremely low temperatures, ice may form in a connection or component. Check for water intrusion. The condition only occurs on a cold start. The condition is not present after the vehicle warms up.
  5. Information from the customer may help to determine if the trouble follows a pattern that is temperature related.

Electromagnetic Interference (EMI) & Electrical Noise

Some electrical components or circuits are sensitive to Electromagnetic Interference (EMI) or other types of electrical noise. Perform the following procedures

  1. Check for a misrouted harness that is too close to a high voltage or high current device. This condition may induce electrical noise on a circuit that could interfere with normal circuit operation. Check for wires that are too close to the following devices: Secondary ignition components. Motors. The generator.
  2. Determine whether the electrical system interference is caused by a malfunctioning relay, PCM driven solenoid or switch. These components may cause a sharp electrical surge. Normally, the problem will occur when the malfunctioning component is operating.
  3. Determine whether non-factory or aftermarket add-on accessories are installed in the vehicle. These accessories may lead to an emission related OBD-II failure. Determine if any of the following non-factory or aftermarket add-on accessories is causing the intermittent: Lights. 2-way radios. Amplifiers. Electric motors. Remote starters. Alarm systems. Cell phones.
  4. Check for an open diode across the A/C compressor clutch and for other open diodes. Some relays may contain a clamping diode.
  5. Check the generator for a bad rectifier bridge that may be allowing AC noise into the electrical system. See ON-VEHICLE TESTING in appropriate GENERATORS & REGULATORS article in ELECTRICAL.

Incorrect PCM Programming

  1. There are only a few situations when reprogramming a PCM is appropriate, such as the following: A new service PCM is installed. A PCM from another vehicle is installed. Revised software or calibration files have been released for this vehicle.
  2. Verify that the PCM contains the correct software or calibration. If incorrect programming is found, reprogram the PCM with the most current software or calibration. See «POWERTRAIN CONTROL MODULE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under PROGRAMMING in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article.

Duplicating Failure Conditions

  1. If none of the previous tests are successful, attempt to duplicate or capture the failure conditions.
  2. Freeze Frame/Failure Records data, where applicable, contains the conditions that were present when the DTC set. Perform the following procedure: Review and record Freeze Frame/Failure Records data. Clear the DTCs using the scan tool. Turn the key to OFF and wait 15 seconds. Operate the vehicle under the same conditions that were noted in Freeze Frame/Failure Records data, as closely as possible. The vehicle must also be operating within the Conditions for Running DTC in the supporting text of the DTC being diagnosed. Monitor DTC Status for the DTC being tested. The scan tool will indicate RAN, when the enabling conditions have been satisfied long enough for the DTC to run. The scan tool will also indicate whether the DTC passed or failed.
  3. An alternate method is to drive the vehicle with the Digital Multimeter (DMM) connected to a suspected circuit. An abnormal reading on the DMM when the problem occurs, may help you locate the problem.

Scan Tool Snapshot

The scan tool can be set up to take a snapshot of the parameters available via serial data. The snapshot function records live data over a period of time. The recorded data can be played back and analyzed. The scan tool can also graph parameters singly or in combinations of parameters for comparison. The snapshot can be triggered manually at the time the symptom is noticed, or set up in advance to trigger when a DTC sets. An abnormal value captured in the recorded data may point to a system or component that needs to be investigated further. Refer to the scan tool user instructions for more information on the Snapshot function.

Vehicle Data Recorder

The Vehicle Data Recorder (J 42598) is connected to the Data Link Connector (DLC) and sent with the customer. The vehicle data recorder captures data for later retrieval and analysis by the technician. Refer to the vehicle data recorder user instructions for more information.

See also:
• DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS
• SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU
• ON-VEHICLE ADJUSTMENTS - CARS
• FUEL SYSTEMS
• FUEL SYSTEM DIAGNOSIS
• NO-START DIAGNOSIS
• BASIC DIAGNOSTIC PROCEDURES - 3.1L CENTURY, GRAND PRIX & MALIBU
• FUEL PUMP ELECTRICAL CIRCUIT DIAGNOSIS
• DTC P0123: THROTTLE POSITION SENSOR CIRCUIT - HIGH VOLTAGE
• ELECTRONIC IGNITION SYSTEM DIAGNOSIS
• EXHAUST GAS RECIRCULATION
• EXHAUST SYSTEM CHECK
• DTC P0401: EGR FLOW INSUFFICIENT
• EXHAUST RESTRICTION
• DTC P0113: INTAKE AIR TEMPERATURE SENSOR CIRCUIT - HIGH VOLTAGE
• DTC P0117: ENGINE COOLANT TEMPERATURE SENSOR CIRCUIT - LOW VOLTAGE
• DTC P0506: IDLE SPEED LOW
• DTC P0507: IDLE SPEED HIGH
• KNOCK SENSOR
• INTERMITTENTS
• PRELIMINARY INSPECTION
• CUTS OUT, MISSES
• ELECTRICAL CONNECTIONS OR WIRING

More articles — Engine Performance