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Engine Controls - Basic Diagnostic Procedures - 3.1l Buick Century VI

Testing & Diagnostics ~8140 words

INTRODUCTION

Before proceeding with basic diagnostic procedures, ensure testing procedure is followed, as some systems which may result in a no-start condition may cause a Diagnostic Trouble Codes (DTC) to be stored in the Powertrain Control Module (PCM). See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article.

If no-start condition still exists after checking and repairing all DTCs, perform a careful and complete visual inspection. Many problems result from mechanical breakdowns, poor electrical connections or damaged/misrouted vacuum hoses. See VISUAL INSPECTION under PRELIMINARY INSPECTION & ADJUSTMENTS. Before condemning the computerized system, perform each test listed in this article.

Note. Perform all voltage tests using a Digital Volt-Ohmmeter (DVOM) or Digital Multimeter (DMM) with a minimum 10-megohm input impedance, unless stated otherwise in test procedure.

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 appropriate VACUUM DIAGRAMS article to verify routing and connections. Inspect air induction system for possible vacuum leaks.

Cylinder Compression Pressure

Note. Remove the Powertrain Control Module (PCM) and the ignition fuses from the I/P fuse block.

A compression pressure test of the engine cylinders determines the condition of the rings, the valves, and the head gasket. Ensure battery is fully charged and starter motor is in good operating condition.

  1. Disable the ignition.
  2. Disable the fuel systems.
  3. Clean spark plug recesses using compressed air. Remove the spark plugs from all the cylinders.
  4. Remove the air duct from the throttle body.
  5. Block the throttle plate in the open position.
  6. Measure the engine compression, using the following procedure: Firmly install the compression gauge to the spark plug hole. Have an assistant crank the engine through at least 4 compression strokes in the testing cylinder. Record the readings on the gauge at each stroke. Disconnect the gauge. Repeat the compression test for each cylinder.
  7. Record the compression readings from all of the cylinders. The lowest reading should not be less than 70 percent of the highest reading. No cylinder reading should be less than 100 psi (689 kPa).
  8. The following list contains examples of the possible measurements: When the compression measurement is normal, the compression builds up quickly and evenly to the specified compression on each cylinder. When the compression is low on the first stroke and tends to build up on the following strokes, but does not reach the normal compression, the piston rings may be the cause. If the compression improves considerably with the addition of three squirts of oil, the piston rings may be the cause. When the compression is low on the first stroke and does not build up in the following strokes, the valves may be the cause. The addition of oil does not affect the compression, the valves may be the cause. When the compression is low on two adjacent cylinders, or coolant is present in the crankcase, the head gasket may be the cause.
  9. Remove the block from the throttle plate.
  10. Install the air duct to the throttle body.
  11. Install the spark plugs.
  12. Install the PCM fuse.
  13. Install the ignition fuse to the I/P fuse block.

Cylinder Leakage

WARNINGBefore servicing any electrical component, the ignition key must be in the OFF or LOCK position and all electrical loads must be OFF, unless instructed otherwise in these procedures. A tool or equipment could easily come in contact with a live exposed electrical terminal, also disconnect the negative battery cable. Failure to follow these precautions may cause personal injury and/or damage to the vehicle or its components.

With the use of air pressure, a cylinder leakage test will aid in the diagnosis. Use the cylinder leakage test in conjunction with the engine compression test in order to isolate the cause of leaking cylinders.

  1. Disconnect the negative battery cable.
  2. Remove the spark plugs.
  3. Install the Cylinder Leakdown Tester (J 35667-A), or equivalent.
  4. Measure each cylinder on the compression stroke, with both valves closed.
  5. Following the manufacturer's instructions, apply air pressure, using the cylinder leakdown tester.
  6. Record the cylinder leakage readings for each cylinder. Normal cylinder leakage is from 12 to 18 percent. Make a note of any cylinder with more leakage than the other cylinders. Any cylinder with 30 percent leakage or more requires service.
  7. Check the 4 primary areas to properly diagnose a leaking cylinder.
  8. If air is heard from the intake or exhaust system, perform the following procedure: Remove the valve rocker arm cover of the suspect cylinder head. Ensure that both valves are closed. Check the cylinder head for a broken valve spring. Remove and inspect the suspect cylinder head. See appropriate article in ENGINES.
  9. If air is heard from the crankcase system at the crankcase, oil filler tube, perform the following procedures. See appropriate article in ENGINES for removal and inspection procedures: Remove the piston from the suspect cylinder. Check the piston and connecting rod assembly. Check the engine block.
  10. If bubbles are found in the radiator, perform the following procedures. See appropriate article in ENGINES for removal and inspection procedures: Remove and inspect both cylinder heads. Check the engine block.
  11. Remove the cylinder leakdown tester.
  12. Install the spark plugs.
  13. Connect the negative battery cable.

Exhaust System Backpressure

For exhaust system backpressure check, go to EXHAUST RESTRICTION under EXHAUST SYSTEM CHECK under EMISSIONS SYSTEM & SUB-SYSTEMS in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.

NO-START DIAGNOSIS

Note. For circuit identification, see WIRING DIAGRAMS .

Note. Some vehicles are equipped with anti-theft systems (VATS or PASSLOCK®) 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 (DTC) in PCM memory.

Note. For component location, see COMPONENT LOCATIONS in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article. For connector terminal identification, see CONNECTOR IDENTIFICATION in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article.

  1. Definition No start is defined as engine cranks properly, but does not start. Engine may fire a few times.

Circuit Description

The Engine Cranks but Does Not Run diagnostic table is an organized approach to identifying a condition that causes an engine not to start. The Engine Cranks but Does Not Run diagnostic table directs the service technician to the appropriate system diagnosis. The Engine Cranks but Does Not Run diagnostic procedure assumes the following

  1. The battery is completely charged.
  2. The engine cranking speed is acceptable.
  3. There is adequate fuel in the fuel tank.

Test Description

The number below refers to the step numbers in the diagnostic procedure.

  1. 7 - If all the Cylinder Injector Circuit Status parameters display Fault, this indicates a condition with the injector supply voltage circuit.
  1. If diagnostic system check has already been performed, go to next step. If diagnostic system check has not been performed, go to «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  2. Turn ignition switch to RUN position, engine OFF. Observe the DTC information using a scan tool. Does the scan tool display DTC P0123, P0230, P0336, P0601, P0602, P1626, P1630 or P1631? If yes, diagnose affected DTC(s). See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article. If no, go to next step.
  3. Turn ignition switch to RUN position, engine OFF. Probe both sides of the FUEL INJR fuse No. 28 (15-amp) and the ELEK IGN fuse No. 25 (15-amp), located in the underhood fuse block, using a test light connected to a good ground. Does the test light illuminate on at least one side of each fuse? If yes, go to next step. If no, go to «IGNITION RELAY DIAGNOSIS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l__ignition-relay) under IGNITION SYSTEMS in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  4. Attempt to start the engine. Observe the engine RPM parameter while the engine is cranking using a scan tool. Does the engine RPM parameter display cranking RPM? If yes, go to next step. If no, go to «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. Command the fuel pump ON using a scan tool. Does the fuel pump turn ON? If yes, go to next step. If no, go to «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.
  6. Turn ignition switch to OFF position. Disconnect a spark plug wire. Install Spark Tester (J 26792), or equivalent to the spark plug wire. Attempt to start the engine. Does the spark tester spark? If yes, go to next step. If no, go to «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.
  7. While monitoring the CYLINDER 1-6 INJECTOR CIRCUIT STATUS parameter using a scan tool, crank the engine. Do all of the cylinder injector circuit status parameters display OK while cranking the engine? If yes, go to next step. If no, go to «FUEL INJECTOR CIRCUIT DIAGNOSIS»(/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.
  8. Turn ignition switch to OFF position. Install all disconnected components. Install Fuel Pressure Gauge (J 34730-1A), or equivalent. Turn ignition switch to RUN position, engine OFF. Command the fuel pump ON using the scan tool. Is the fuel pressure 52-59 psi (358-405 kPa) when the fuel pump is operating? If yes, go to next step. If no, go to «FUEL SYSTEM DIAGNOSIS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-31l__fuel-system-diagnosis) under FUEL SYSTEMS.
  9. Check for the following conditions: Collapsed air intake duct. Restricted air filter element. Spark plugs for being gas or coolant fouled. If the spark plugs are fouled, determine what caused the condition. Engine mechanical condition. For example, worn timing chain and gears, low compression. See appropriate article in ENGINES. Restricted exhaust system. 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 in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article. The Engine Coolant Temperature (ECT) sensor parameter is NOT close to the actual engine temperature. See «DTC P0117: ENGINE COOLANT TEMPERATURE SENSOR»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__dtc-p0117-engine-coolant-temperature-sensor) or «DTC P0118: ENGINE COOLANT TEMPERATURE SENSOR»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__dtc-p0118-engine-coolant-temperature-sensor) under DIAGNOSTIC TESTS in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article. Compare Manifold Absolute Pressure/Barometric Pressure (MAP/BARO) parameters to another vehicle. The parameters should be close in value. See «MANIFOLD ABSOLUTE PRESSURE SENSOR»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) under SENSORS & SWITCHES in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article. TP sensor for being stuck in range. See «DTC P0121: TP SENSOR PERFORMANCE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under DIAGNOSTIC TESTS in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article. After completing inspections, go to next step.
  10. Clear the DTCs using a scan tool. Attempt to start the engine. Does the engine start and continue to operate? If yes, go to next step. If no, go to step 2 .
  11. Allow engine to reach operating temperature. Observe DTC information using scan tool. Are there any DTCs that have not been diagnosed? If yes, diagnose affected DTC(s). See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article. If no, system is okay at this time.

The Engine Cranks but Does Not Run diagnostic table is an organized approach to identifying a condition that causes an engine not to start. The Engine Cranks but Does Not Run diagnostic table directs the service technician to the appropriate system diagnosis. The Engine Cranks but Does Not Run diagnostic table assumes the following

  1. The battery is completely charged.
  2. The engine cranking speed is acceptable.
  3. There is adequate fuel in the fuel tank.

The number below refers to the step numbers in the diagnostic procedure.

  1. 7 - If all the Cylinder Injector Circuit Status parameters display Fault, this indicates a condition with the injector supply voltage circuit.
  1. If diagnostic system check has already been performed, go to next step. If diagnostic system check has not been performed, go to «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  2. Turn ignition switch to RUN position, engine OFF. Observe the DTC information using a scan tool. Does the scan tool display DTC P0230, P0336, P0601, P0602, P1626, P1629, P1630 or P1631? If yes, diagnose affected DTC(s). See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article. If no, go to next step.
  3. Turn ignition switch to RUN position, engine OFF. Probe both sides of the ignition fuse No. 21 (15-amp) and the ELEK IGN fuse No. 25 (15-amp), located in the underhood fuse block using a test light connected to a good ground. Does the test light illuminate on at least one side of each fuse? If yes, go to next step. If no, go to «IGNITION RELAY DIAGNOSIS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l__ignition-relay) under IGNITION SYSTEMS in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  4. Attempt to start the engine. Observe the engine RPM parameter while the engine is cranking using a scan tool. Does the engine RPM parameter display cranking RPM? If yes, go to next step. If no, go to «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. Command the fuel pump ON using a scan tool. Does the fuel pump turn ON? If yes, go to next step. If no, go to «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.
  6. Turn ignition switch to OFF position. Disconnect a spark plug wire. Install Spark Tester (J 26792), or equivalent, to the spark plug wire. Attempt to start the engine. Does the spark tester spark? If yes, go to next step. If no, go to «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.
  7. While monitoring the CYLINDER 1-6 INJECTOR CIRCUIT STATUS parameter using a scan tool, crank the engine. Do all of the cylinder injector circuit status parameters display OK while cranking the engine? If yes, go to next step. If no, go to «FUEL INJECTOR CIRCUIT DIAGNOSIS»(/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.
  8. Turn ignition switch to OFF position. Install all disconnected components. Install Fuel Pressure Gauge (J 34730-1A), or equivalent. Turn ignition switch to RUN position, engine OFF. Command the fuel pump ON using the scan tool. Is the fuel pressure 52-59 psi (358-405 kPa) when the fuel pump is operating? If yes, go to next step. If no, go to «FUEL SYSTEM DIAGNOSIS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-31l__fuel-system-diagnosis) under FUEL SYSTEMS.
  9. Check for the following conditions: Collapsed air intake duct. Restricted air filter element. Spark plugs for being gas or coolant fouled. If the spark plugs are fouled, determine what caused the condition. Engine mechanical condition. For example, worn timing chain and gears, low compression. See appropriate article in ENGINES. Restricted exhaust system. 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 in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article. The Engine Coolant Temperature (ECT) sensor parameter is NOT close to the actual engine temperature. See «DTC P0117: ENGINE COOLANT TEMPERATURE SENSOR»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__dtc-p0117-engine-coolant-temperature-sensor) or «DTC P0118: ENGINE COOLANT TEMPERATURE SENSOR»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__dtc-p0118-engine-coolant-temperature-sensor) under DIAGNOSTIC TESTS in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article. Compare Manifold Absolute Pressure/Barometric Pressure (MAP/BARO) parameters to another vehicle. The parameters should be close in value. See «MANIFOLD ABSOLUTE PRESSURE SENSOR»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) under SENSORS & SWITCHES in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article. TP sensor for being stuck in range. See «DTC P0121: TP SENSOR PERFORMANCE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under DIAGNOSTIC TESTS in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article. After completing inspections, go to next step.
  10. Clear the DTCs using a scan tool. Attempt to start the engine. Does the engine start and continue to operate? If yes, go to next step. If no, go to step 2 .
  11. Allow engine to reach operating temperature. Observe DTC information using scan tool. Are there any DTCs that have not been diagnosed? If yes, diagnose affected DTC(s). See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article. If no, system is okay at this time.

The Engine Cranks but Does Not Run diagnostic table is an organized approach to identifying a condition that causes an engine not to start. The Engine Cranks but Does Not Run diagnostic table directs the service technician to the appropriate system diagnosis. The Engine Cranks but Does Not Run diagnostic table assumes the following

  1. The battery is completely charged.
  2. The engine cranking speed is acceptable.
  3. There is adequate fuel in the fuel tank.
  1. If diagnostic system check has already been performed, go to next step. If diagnostic system check has not been performed, go to «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  2. Crank the engine for 15 seconds. Turn ignition switch to RUN position, engine OFF. Observe the DTC information using a scan tool. Does the scan tool display DTC P0101, P0123, P0230, P0336, P0601, P0602, P1626, P1630, P1631, B1369 or B1379? If yes, diagnose affected DTC(s). See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article. If no, go to next step.
  3. Turn ignition switch to RUN position, engine OFF. Is the MIL illuminated? If yes, go to next step. If no, go to «MIL INOPERATIVE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__mil-inoperative) under SYSTEM TESTS in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  4. Command the fuel pump ON using a scan tool. Does the fuel pump turn ON? If yes, go to next step. If no, go to «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. Turn ignition switch to OFF position. Disconnect a spark plug wire. Install Spark Tester (J 26792), or equivalent to the spark plug wire. Attempt to start the engine. Does the spark tester spark? If yes, go to next step. If no, go to «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.
  6. While monitoring the CYLINDER 1-6 INJECTOR CIRCUIT STATUS parameter using a scan tool, crank the engine. Do all of the cylinder injector circuit status parameters display OK while cranking the engine? If yes, go to next step. If no, go to «FUEL INJECTOR CIRCUIT DIAGNOSIS»(/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.
  7. Turn ignition switch to OFF position. Install all disconnected components. Install Fuel Pressure Gauge (J 34730-1A), or equivalent. Turn ignition switch to RUN position, engine OFF. Command the fuel pump ON using the scan tool. Is the fuel pressure 52-59 psi (358-405 kPa) when the fuel pump is operating? If yes, go to next step. If no, go to «FUEL SYSTEM DIAGNOSIS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-31l__fuel-system-diagnosis) under FUEL SYSTEMS.
  8. Check for the following conditions: Collapsed air intake duct. Restricted air filter element. Spark plugs for being gas or coolant fouled. If the spark plugs are fouled, determine what caused the condition. Engine mechanical condition. For example, worn timing chain and gears, low compression. See appropriate article in ENGINES. Restricted exhaust system. 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 in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article. The Engine Coolant Temperature (ECT) sensor parameter is NOT close to the actual engine temperature. See «DTC P0128: ENGINE COOLANT TEMPERATURE BELOW THERMOSTAT REGULATING TEMPERATURE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__dtc-p0128-engine-coolant-temperature-below) under DIAGNOSTIC TESTS in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article. Compare Manifold Absolute Pressure/Barometric Pressure (MAP/BARO) parameters to another vehicle. The parameters should be close in value. See «MANIFOLD ABSOLUTE PRESSURE SENSOR»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) under SENSORS & SWITCHES in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article. TP sensor for being stuck in range. See «DTC P0121: TP SENSOR PERFORMANCE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) under DIAGNOSTIC TESTS in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article. After completing inspections, go to next step.
  9. Clear the DTCs using a scan tool. Attempt to start the engine. Does the engine start and continue to operate? If yes, go to next step. If no, go to step 2 .
  10. Allow engine to reach operating temperature. Observe DTC information using scan tool. Are there any DTCs that have not been diagnosed? If yes, diagnose affected DTC(s). See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article. If no, system is okay at this time.

FUEL SYSTEMS

Basic diagnosis of fuel system should begin by checking fuel pump operation and fuel pressure.

WARNINGHigh fuel pressure may be present in fuel lines and component parts. ALWAYS release fuel pressure before disconnecting any fuel injection-related component. DO NOT allow fuel to contact engine or electrical components.

FUEL SYSTEM PRESSURE RELIEF

WARNINGRemove the fuel tank cap and relieve the fuel system pressure before servicing the fuel system in order to reduce the risk of personal injury. After you relieve the fuel system pressure, a small amount of fuel may be released when servicing the fuel lines, the fuel injection pump, or the connections. In order to reduce the risk of personal injury, cover the fuel system components with a shop towel before disconnection. This will catch any fuel that may leak out. Place the towel in an approved container when the disconnection is complete.
  1. Disconnect the negative battery cable.
  2. Install the Fuel Pressure Gauge Fitting (J 34730-262), or equivalent, to the fuel pressure connection.
  3. Connect Fuel Pressure Fitting (J 34730-1A), or equivalent, to the fuel pressure gauge fitting. Wrap a shop towel around the fuel pressure connection while connecting the fuel pressure gauge to avoid spillage.
  4. Install the bleed hose into an approved container and open the valve to bleed the system pressure. The fuel connections are now safe for servicing.
  5. Drain any fuel remaining in the fuel pressure gauge into an approved container.

FUEL SYSTEM DIAGNOSIS

Note. For component location, see COMPONENT LOCATIONS in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article. For connector terminal identification, see CONNECTOR IDENTIFICATION in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article. For circuit identification, see WIRING DIAGRAMS .

System Description

When the ignition is turned ON, the Powertrain Control Module (PCM) turns ON the fuel pump relay, which turns ON the in-tank fuel pump. The in-tank fuel pump remains ON as long as the engine is cranking or running and the PCM is receiving ignition reference pulses. If there are no ignition reference pulses, the PCM turns the in-tank fuel pump OFF 2 seconds after the ignition is turned ON or 2 seconds after the engine stops running.

The in-tank fuel pump is an electric pump attached to the fuel sender assembly. The fuel pump is designed to provide fuel at a pressure above the pressure needed by the fuel injectors. A fuel pressure regulator, attached to the fuel rail, keeps the fuel available to the fuel injectors at a regulated pressure. Unused fuel is returned to the fuel tank by a separate fuel return pipe.

The numbers below refer to the step numbers in the diagnostic procedure.

  1. 2 - This step verifies that the fuel pump is operating.
  2. 4 - This step tests for an internal fuel leak. If the fuel pressure drops during this test, then an internal loss of pressure is indicated.
  3. 6 - This step tests the fuel pressure regulator. The fuel pressure regulator is controlled by engine vacuum. With engine vacuum applied, the pressure should drop the specified value.
  4. 9 - This step inspects the fuel pressure regulator for a fuel leak from the vacuum port. If fuel leaks from the fuel pressure regulator while the fuel pump is commanded ON, replace the fuel pressure regulator.
  5. 10 - This step tests for a loss of fuel pressure between the fuel feed pipe shut-off adapter and the fuel pump.
  6. 11 - This step tests for a leaking fuel injector, or fuel pressure regulator. If the fuel pressure remains constant during this test, the fuel injectors are not leaking fuel.
  7. 14 - This step tests for a restricted fuel return pipe. If the fuel pressure is within the specified values, a restriction in the fuel return pipe is indicated.
  8. 16 - This step determines if the fuel pressure regulator, or the fuel pump, is the cause of the low fuel pressure. If the pressure rises above the specified value, the fuel pump is okay.
  1. If diagnostic system check has already been performed, go to next step. If diagnostic system check has not been performed, go to «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  2. Turn ignition switch to RUN position, engine OFF. Command the fuel pump ON using a scan tool. Does the fuel pump operate? If yes, go to next step. If no, go to «FUEL PUMP ELECTRICAL CIRCUIT DIAGNOSIS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-31l__fuel-pump-electrical-circuit-diagnosis) .
  3. Turn ignition switch to OFF position. Turn OFF all accessories Install Fuel Pressure Gauge (J 34730-1A), or equivalent and the fuel pressure gauge fitting. Turn ignition switch to RUN position, engine OFF. Command the fuel pump relay ON using a scan tool. The fuel pump runs for approximately 2 seconds. Command the fuel pump relay ON using a scan tool to obtain the highest possible fuel pressure. Do not start the engine. Observe the fuel pressure gauge, with the fuel pump relay commanded ON. Is the fuel pressure 52-59 psi (358-405 kPa)? If yes, go to next step. If no, go to step 12 .
  4. Monitor the fuel pressure gauge for one minute. Does the fuel pressure decrease by more than 5 psi (34 kPa)? If yes, go to step 9 . If no, go to step 6 .
  5. Relieve the fuel pressure to 10 psi (69 kPa). Monitor the fuel pressure gauge for 5 minutes. Does the fuel pressure decrease by more than 2 psi (14 kPa)? If yes, go to step 24 . If no, go to next step.
  6. Turn ignition switch to OFF position for 15 seconds. Turn ignition switch to RUN position, engine OFF. Monitor the fuel pressure gauge. Start the engine. Does the fuel pressure decrease by 3-10 psi (21-69 kPa) when the engine is started? If yes, go to next step. If no, go to step 8 .
  7. Operate the vehicle within the conditions of the customers concern. Monitor the fuel trim and HO2S parameters using a scan tool. Do any of the scan tool parameters indicate a lean condition? If yes, go to step 17 . If no, go to «DIAGNOSTIC AIDS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-31l__diagnostic-aids) .
  8. Disconnect the vacuum hose from the fuel pressure regulator. Monitor the fuel pressure gauge. Idle the engine. Apply 12-14 in. Hg. (34-47 kPa) of vacuum to the fuel pressure regulator using Vacuum Pump (J 23738-A), or equivalent. Does the fuel pressure decrease by 3-10 psi (21-69 kPa) when the vacuum is applied? If yes, go to step 21 . If no, go to step 23 .
  9. Turn ignition switch to OFF position. Remove the vacuum hose from the fuel pressure regulator. Turn ignition switch to RUN position, engine OFF. Command the fuel pump ON using a scan tool. Inspect for a fuel leak from the fuel pressure regulator vacuum port. Is the fuel pressure regulator leaking fuel? If yes, go to step 23 . If no, go to next step.
  10. Turn ignition switch to OFF position. Relieve the fuel pressure. See «FUEL SYSTEM PRESSURE RELIEF»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-31l__fuel-system-pressure-relief) . Disconnect the fuel feed hose and the fuel return hose from the fuel rail pipes. Install Fuel Pipe Line Shut-Off Adapters (J 37287), or equivalent, between the fuel hoses and the fuel rail pipes. Open the valves on the shut-off adapters. Turn ignition switch to RUN position, engine OFF. Command the fuel pump relay ON using a scan tool. Bleed the air from the fuel pressure gauge. Close the fuel feed pipe shut-off valve. Command the fuel pump relay ON using a scan tool to obtain the highest possible fuel pressure. Monitor the fuel pressure gauge for one minute. Does the fuel pressure remain constant? If yes, go to step 19 . If no, go to next step.
  11. Turn ignition switch to OFF position. Open the fuel feed pipe shut-off valve. Turn ignition switch to RUN position, engine OFF. Command the fuel pump relay ON and then OFF using a scan tool. Close the fuel return pipe shut-off valve. Monitor the fuel pressure gauge for one minute. Does the fuel pressure remain constant? If yes, go to step 23 . If no, go to step 20 .
  12. Is the fuel pressure above 59 psi (407 kPa)? If yes, go to step 14 . If no, go to next step.
  13. Is the fuel pressure above zero psi (zero kPa)? If yes, go to step 16 . If no, go to step 17 .
  14. Turn ignition switch to OFF position. Relieve the fuel pressure. See «FUEL SYSTEM PRESSURE RELIEF»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-31l__fuel-system-pressure-relief) . Disconnect the fuel return hose from the fuel rail return pipe. Attach a length of flexible fuel hose to the fuel rail outlet passage. Place the open end of the flexible fuel hose into an approved gasoline container. Turn ignition switch to RUN position, engine OFF. Monitor the fuel pressure gauge while the fuel pump is operating. Is the fuel pressure 52-59 psi (358-407 kPa)? If yes, go to step 22 . If no, go to next step.
  15. Inspect the fuel rail return pipe and fuel rail outlet passage for a restriction. Did you find and correct the condition? If yes, go to step 25 . If no, go to step 23 .
  16. Turn ignition switch to OFF position. Relieve the fuel pressure. See «FUEL SYSTEM PRESSURE RELIEF»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-31l__fuel-system-pressure-relief) . Disconnect the fuel return hose from the fuel rail return pipe. Install the shut-off adapters between the fuel return pipe and the fuel rail. Open the valve in the shut-off adapters. Turn ignition switch to RUN position, engine OFF. Bleed the air from the fuel system. Monitor the fuel pressure gauge. DO NOT allow the fuel pressure to exceed 75 psi (517 kPa). Excessive pressure may damage the fuel system. Slowly close the valve in the fuel return pipe shut-off adapter. Command the fuel pump relay ON using a scan tool. Does the fuel pressure rise above 52 psi (358 kPa)? If yes, go to step 23 . If no, go to next step.
  17. Inspect the fuel filter and fuel feed pipe for a restriction. Did you find and correct the condition? If yes, go to step 25 . If no, go to next step.
  18. Inspect the harness connectors and ground circuits of the fuel pump for poor connections. Did you find and correct the condition? If yes, go to step 25 . If no, go to next step.
  19. Remove the fuel sender assembly. Inspect the fuel pump flex hose for damage, the in-tank fuel pump harness connectors for poor connections, the fuel strainer for a restriction and contaminates in the fuel tank. Did you find and correct the condition? If yes, go to step 25 . If no, go to step 24 .
  20. Turn ignition switch to OFF position. Raise the fuel rail, with the fuel lines connected. Turn ignition switch to RUN position, engine OFF. Command the fuel pump relay ON using a scan tool. Locate and replace the leaking fuel injector. After repair, go to step 25 .
  21. Repair the vacuum source to the fuel pressure regulator. After repair, go to step 25 .
  22. Locate and repair the restricted fuel return line. After repair, go to step 25 .
  23. Inspect for a missing or damaged fuel pressure regulator "O" ring before replacing the fuel pressure regulator. Replace the fuel pressure regulator if "O" ring is okay. After repair, go to step 25 .
  24. Replace the fuel pump. After repair, go to next step.
  25. Operate the system to verify the repair. Did you correct the condition? If yes, system is okay at this time. If no, go to step 3 .

Diagnostic Aids

  1. A hard start or long crank time when the engine is cold can be caused by low fuel pump volume.
  2. The fuel pressure should build quickly when the fuel pump is commanded ON.
  3. If you must command the fuel pump on several times for the fuel pressure to build, suspect low fuel pump volume.
  4. For an intermittent condition, see «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.

FUEL PUMP ELECTRICAL CIRCUIT DIAGNOSIS

Note. For component location, see COMPONENT LOCATIONS in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article. For connector terminal identification, see CONNECTOR IDENTIFICATION in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article. For circuit identification, see WIRING DIAGRAMS .

When the ignition is turned ON, the Powertrain Control Module (PCM) turns ON the fuel pump relay, which turns ON the in-tank fuel pump. The in-tank fuel pump remains ON as long as the engine is cranking or running and the PCM is receiving reference pulses. If there are no reference pulses, the PCM turns the in-tank fuel pump OFF 2 seconds after the ignition is turned ON or 2 seconds after the PCM no longer receives reference pulses.

The numbers below refer to the step numbers in the diagnostic procedure.

  1. 3 - This step determines if the condition is located on the coil side or the switch side of the circuit.
  2. 4 - This step verifies that the PCM is providing voltage to the fuel pump relay.
  3. 5 - This step tests for an open in the ground circuit to the fuel pump relay.
  4. 6 - This step determines if a voltage is constantly being applied to the fuel pump relay.
  5. 13 - This step determines if the condition with the circuit is intermittent. If the fuse does not open, inspect the supply voltage circuit between the fuse and the fuel pump for an intermittent condition.
  1. If diagnostic system check has already been performed, go to next step. If diagnostic system check has not been performed, go to «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  2. Turn ignition switch to RUN position, engine OFF. Using a scan tool, command the fuel pump relay ON and OFF. Does the fuel pump turn ON and OFF? If yes, go to «DIAGNOSTIC AIDS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-31l) . If no, go to next step.
  3. Using a scan tool, command the fuel pump relay ON and OFF. Do you hear a click when you command the fuel pump relay ON and OFF? If yes, go to step 9 . If no, go to next step.
  4. Turn ignition switch to OFF position. Disconnect the fuel pump relay. Turn ignition switch to RUN position, engine OFF. Probe the fuel pump relay control circuity using a test light connected to a good ground. Using a scan tool, command the fuel pump relay ON and OFF. Does the test light turn ON and OFF? If yes, go to next step. If no, go to step 6 .
  5. Connect a test light between the control circuit of the fuel pump relay and the ground circuit of the fuel pump relay. Using a scan tool, command the fuel pump relay ON and OFF. Does the test light turn ON and OFF as commanded? If yes, go to step 19 . If no, go to step 22 .
  6. Does the test light remain illuminated with each command? If yes, go to next step. If no, go to step 8 .
  7. Test the fuel pump relay control circuit for a short to voltage. Did you find and correct the condition? If yes, go to step 27 . If no, go to step 26 .
  8. Test the fuel pump relay control circuit for a short to ground or an open. Did you find and correct the condition? If yes, go to step 27 . If no, go to step 20 .
  9. Turn ignition switch to RUN position, engine OFF. Does the fuel pump operate continuously? If yes, go to next step. If no, go to step 11 .
  10. Turn ignition switch to OFF position. Disconnect the fuel pump relay. Turn ignition switch to RUN position, engine OFF. Does the fuel pump operate continuously? If yes, go to step 21 . If no, go to step 25 .
  11. Is the fuel pump fuse open? If yes, go to next step. If no, go to step 14 .
  12. Test the fuel pump supply voltage circuit for a grounded circuit between the fuel pump fuse and the fuel pump. Replace the fuel pump fuse if necessary. Did you find and correct the condition? If yes, go to step 27 . If no, go to next step.
  13. Install all disconnected electrical components. Install a new fuel pump fuse. Using a scan tool, turn ON the fuel pump relay. Inspect the fuel pump fuse. Is the fuel pump fuse open? If yes, go to step 24 . If no, go to «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  14. Turn ignition switch to OFF position. Disconnect the fuel pump relay. Turn ignition switch to RUN position, engine OFF. Probe the fuel pump relay switch battery voltage circuit using a test light connected to a good ground. Does the test light illuminate? If yes, go to next step. If no, go to step 23 .
  15. Connect a 20-amp fused jumper wire between the fuel pump relay switch battery voltage circuit and the fuel pump supply voltage circuit. Does the fuel pump operate? If yes, go to step 19 . If no, go to next step.
  16. Test the fuel pump supply voltage circuit for an open or high resistance between the fuel pump relay and the fuel pump. Did you find and correct the condition? If yes, go to step. 27 . If no, go to next step.
  17. Inspect the ground circuit for being tight, corrosion on terminals, or damage to the wiring harness. Test the fuel pump ground circuit for an open or high resistance. Did you find and correct the condition? If yes, go to step 27 . If no, go to next step.
  18. Inspect for poor connections at the fuel pump. Did you find and correct the condition? If yes, go to step 27 . If no, go to step 24 .
  19. Inspect for poor connections at the fuel pump relay. Did you find and correct the condition? If yes, go to step 27 . If no, go to step 25 .
  20. Inspect for poor connections at the harness connector of the PCM. Did you find and correct the condition? If yes, go to step 27 . If no, go to step 26 .
  21. Repair the supply voltage circuit of the fuel pump for a short to voltage. After repair, go to step 27 .
  22. Repair the open fuel pump relay ground circuit. After repair, go to step 27 .
  23. Repair the battery voltage circuit of the fuel pump relay switch. After repair, go to step 27 .
  24. Replace the fuel pump. Replace the fuel pump fuse if necessary. After repair, go to step 27 .
  25. Replace the fuel pump relay. After repair, go to step 27 .
  26. Replace PCM. See appropriate REMOVAL & INSTALLATION article. Perform PCM relearn procedure. 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. After repair, go to next step.
  27. Operate the system to verify the repair. Did you correct the condition? If yes, system is okay at this time. If no, go to step 3 .
  1. Inspect the ground connection for the fuel pump. Ensure all ground connections are clean and tight.
  2. The following conditions may have caused the fuel pump fuse to open: The fuse is faulty. There is an intermittent short in the fuel pump power feed circuit. The fuel pump has an intermittent internal problem.
  3. For an intermittent condition, see «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.

FUEL PRESSURE TEST

Note. Manufacturer does not provide testing procedures for many individual systems and components. For fuel system pressure test, perform FUEL SYSTEM DIAGNOSIS .

IGNITION SYSTEMS

Note. For additional ignition system and component diagnosis, see IGNITION SYSTEMS in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.

Note. For circuit identification, see WIRING DIAGRAMS .

CAMSHAFT POSITION SENSOR

A malfunction in Camshaft Position (CMP) sensor can set a DTC. For testing procedures and specifications, perform appropriate diagnostic test. See DIAGNOSTIC TROUBLE CODE DEFINITIONS in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article.

CRANKSHAFT POSITION SENSOR

A malfunction in Crankshaft Position (CKP) sensor can set a DTC. For testing procedures and specifications, perform appropriate diagnostic test. See DIAGNOSTIC TROUBLE CODE DEFINITIONS in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article.

IGNITION CONTROL MODULE

A malfunction in Ignition Control Module (ICM) can set a DTC. For testing procedures and specifications, perform appropriate diagnostic test. See DIAGNOSTIC TROUBLE CODE DEFINITIONS in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article.

The Ignition Control Module (ICM) has independent power and ground circuits. The circuits between the ICM and the Powertrain Control Module (PCM) consist of the following circuits

  1. The IC timing signal.
  2. The IC timing control.
  3. The low-resolution engine speed signal.
  4. A low reference signal.

The ICM sends 3X signals to the PCM. The ICM controls the timing advance during engine cranking. The timing advance changes to PCM control after the following actions

  1. The PCM receives the second 3X signal.
  2. The PCM applies 5 volts to the IC timing signal circuit.
  1. If diagnostic system check has already been performed, go to next step. If diagnostic system check has not been performed, go to «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine) in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  2. Attempt to start the engine. Does the engine start and run? If yes, go to next step. If no, go to step 4 .
  3. Disconnect the Crankshaft Position (CKP) sensor "B" harness connector from the Ignition Control Module (ICM). Measure the resistance from the CKP sensor 1 signal circuit to the low reference circuit of CKP sensor "B" using a DMM. Is the resistance 800-1200 ohms? If yes, go to next step. If no, go to step 28 .
  4. Disconnect the Crankshaft Position (CKP) sensor "A". Observe the 3X crank sensor parameter using a scan tool. Crank the engine. Does the scan tool indicate a 3X crank sensor signal present? If yes, go to next step. If no, go to step 11 .
  5. Connect the CKP sensor "A". Test for spark at each cylinder using Spark Tester (J 26792), or equivalent. Did you observe any non-sparking cylinders? If yes, go to next step. If no, go to step 9 .
  6. Check and test the affected cylinder spark plug wires, the ignition coils, and the spark plugs for a short to ground or an arching to ground. If carbon tracking or corrosion is present, replace both components that are affected. Did you find and correct the condition? If yes, go to step 32 . If no, go to next step.
  7. Test the resistance of the spark plug wires. Is the resistance more than 3000 ohms per foot? If yes, go to step 30 . If no, go to next step.
  8. Measure the secondary resistance of the ignition coils. Is the resistance 5-8 k/ohms? If yes, go to step 25 . If no, go to step 29 .
  9. Check the spark plug wires for proper routing and for the correct firing order. If any spark plug wires are found to be misrouted, reroute as necessary. Did you find and correct the condition? If yes, go to step 32 . If no, go to next step.
  10. Remove the spark plugs. Inspect spark plugs. Did you find the problem? If yes, go to step 31 . If no, go to «DIAGNOSTIC AIDS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-31l) .
  11. Connect the CKP sensor "A". Disconnect the ICM harness connector. Turn ignition switch to RUN position. Connect a test light between the ICM ignition 1 voltage circuit and a good ground. Does the test light illuminate? If no, go to next step. If no, go to step 24 .
  12. Connect a test light between the ICM ignition 1 voltage circuit and the ICM ground. Does the test light illuminate? If yes, go to next step. If no, go to step 26 .
  13. Test for an intermittent and for a poor connection at the ICM. Did you find and correct the condition? If yes, go to step 32 . If no, go to next step.
  14. Disconnect the CKP sensor "B" connector from the ICM. Probe the CKP sensor "B" CKP sensor 1 signal circuit using a test light connected to battery voltage. Does the test light illuminate? If yes, go to step 17 . If no, go to next step.
  15. Probe the CKP sensor "B" CKP sensor 1 signal circuit using a test light connected to a good ground. Does the test light illuminate? If yes, go to step 18 . If no, go to next step.
  16. Turn ignition switch to OFF position. Measure the resistance from the CKP sensor "B" CKP sensor 1 signal circuit and the low reference circuit using the DMM at the ICM harness connector. Is the resistance 800-1200 ohms? If yes, go to step 27 . If no, go to step 19 .
  17. Test the CKP sensor 1 signal circuit for a short to ground. Did you find and correct the condition? If yes, go to step 32 . If no, go to step 20 .
  18. Test the CKP sensor 1 signal circuit for a short to voltage. Did you find and correct the condition? If yes, go to step 32 . If no, go to step 17 .
  19. Test the CKP sensor "B" circuits for an open, or the CKP sensor 1 signal and the low reference circuit shorted together. Did you find and correct the condition? If yes, go to step 32 . If no, go to step 17 .
  20. Test for an intermittent and for a poor connection at the ICM. Did you find and correct the condition? If yes, go to step 32 . If no, go to next step.
  21. Test for an intermittent and for a poor connection at the CKP sensor. Did you find and correct the condition? If yes, go to step 32 . If no, go to next step.
  22. Remove the CKP sensor. Visually inspect the CKP sensor for the following conditions: Physical damage. Loose or improper installation. Wiring routed too closely to secondary ignition components. Did you find and correct the condition? If yes, go to step 32 . If no, go to next step.
  23. Visually inspect the reluctor wheel for physical damage and loose or improper installation. Did you find and correct the condition? If no, go to step 32 . If no, go to step 28 .
  24. Repair the open or the short to ground in the ICM ignition 1 voltage circuit. After repair, go to step 32 .
  25. Remove the coils associated with the cylinder that did not have spark. Connect a test light across the ignition module primary circuit, between the ICM terminals for the coils. Observe the test light while cranking the engine. Does the test light flash continuously while the engine is being cranked? If yes, go to step 29 . If no, go to step 27 .
  26. Repair the open in the ICM ground circuit. After repair, go to step 32 .
  27. Replace the ICM. After repair, go to step 32 .
  28. Replace the CKP sensor "B". After repair, go to step 32 .
  29. Replace the affected ignition coils. After repair, go to step 32 .
  30. Replace the spark plug wires. After repair, go to step 32 .
  31. Replace the spark plugs. After repair, go to next step.
  32. Turn ignition witch to OFF position for 30 seconds. Start the engine and operate the vehicle. Observe the Malfunction Indicator Light (MIL), vehicle performance and driveability. Does the vehicle operate normally, with no MIL? If yes, system is okay at this time. If no, go to step 2 .
  1. An arcing spark plug wire or an arcing ignition coil to the ICM may cause a stall, misfire or a no start condition.
  2. The following may cause a no start condition: Crankshaft reluctor wheel damage or improper installation. The CKP sensor coming in contact with the reluctor wheel. Foreign material passing between the CKP sensor and the reluctor wheel.
  3. Excess crankshaft end play will cause the CKP sensor reluctor wheel to move out of alignment with the CKP sensor. This could result in any of the following conditions: A no start. A start and stall. Erratic performance.
  4. An improperly installed crankshaft could cause excess crankshaft end play.

IDLE SPEED & IGNITION TIMING

Idle speed and ignition timing are controlled by PCM. Incorrect idle speed are normally caused by dirty throttle plate or vacuum leaks. Ensure all vacuum components are functioning properly. Ensure idle speed and ignition timing are set to specification. For specifications and adjustments, see appropriate SERVICE & ADJUSTMENT SPECIFICATIONS and ON-VEHICLE ADJUSTMENTS articles.

CENTURY

See ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS article in ELECTRICAL.

GRAND PRIX

See ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS article in ELECTRICAL.

MALIBU

See ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS article in ELECTRICAL.

More articles — Engine Performance