Engine Controls - System Testing & Engine Component Tests - 3.1l Buick Century VI

INTRODUCTION

Before testing separate components or systems, follow proper workflow. See DIAGNOSTIC STARTING POINT - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article. If no Diagnostic Trouble Codes (DTC) are present and a no-start condition exists, proceed to BASIC DIAGNOSTIC PROCEDURES - 3.1L CENTURY, GRAND PRIX & MALIBU article. If no DTCs are present and a driveability condition exists, proceed to TROUBLE SHOOTING - NO CODES - 3.1L CENTURY, GRAND PRIX & MALIBU article for diagnosis by symptom (i.e., ROUGH IDLE, ENGINE STALLS, etc.).

Note. Testing individual components does not isolate shorts or opens. Perform all voltage tests using a DVOM with a minimum 10-megohm input impedance, unless stated otherwise in test procedure. Use ohmmeter to isolate wiring harness shorts or opens.

COMPONENT LOCATIONS

Note. To aid in component location, refer to illustrations. See COMPONENT LOCATIONS in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article.

COMPONENT LOCATIONS (CENTURY)

COMPONENT LOCATIONS (CENTURY)

COMPONENT LOCATIONS (GRAND PRIX)

COMPONENT LOCATIONS (GRAND PRIX)

COMPONENT LOCATIONS (MALIBU)

COMPONENT LOCATIONS (MALIBU)

AIR INDUCTION SYSTEMS

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

Note. For component locations, see COMPONENT LOCATIONS .

COMPUTERIZED ENGINE CONTROLS

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

Ground Circuits

1. Using DVOM, check for continuity to ground at PCM ground terminals. Resistance should be less than 5 ohms. If resistance is not less than 5 ohms, repair open or high resistance in ground circuit.
2. Connect negative lead of DVOM to a known-good ground. Backprobe positive lead of voltmeter to each PCM ground terminal. With vehicle running, DVOM should indicate less than one volt. If DVOM reading is greater than one volt, check for open, short to voltage, corrosion or loose connection in ground circuit.

Power Circuits

1. Using DVOM, check for battery voltage between PCM continuous power terminal(s) and ground. If battery voltage is not present, check for open fuse or fusible link. If fuse or fusible link is okay, check for open in circuit between PCM continuous power terminal and power source.
2. Turn ignition switch to RUN position. Using DVOM, check for battery voltage between PCM ignition power terminals and ground. If battery voltage is not present, check IGN fuse. If fuse is okay, check for open in circuit between battery and ignition switch, and between ignition switch and PCM ignition power terminal. If circuits are okay, check for defective ignition switch.
3. Connect DVOM between ground and PCM starter (crank) signal terminal. Place gearshift lever in Park. On all vehicles, turn ignition switch to START position. Battery voltage should be present only when ignition switch is in START position.
4. If voltage is not present, check underhood fuse block fuse No. 5. If fuse is okay, check for open in circuit between ignition switch and PCM starter (crank) signal terminal, or check for defective ignition switch.

PCM Harness Resistance

Turn ignition switch to LOCK position. Disconnect PCM and related component harness connectors. Check for open or short circuits between PCM harness connector terminal and component harness connector terminal. For connector terminal identification, see SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article. See WIRING DIAGRAMS . If harness is open or shorted, repair as necessary.

SENSORS & SWITCHES

Note. For additional sensor testing specifications, see appropriate SENSOR OPERATING RANGE CHARTS article.

Manufacturer does not provide testing procedures for many individual systems and components. For sensor and switch testing not listed, perform related DTC testing procedure. See DIAGNOSTIC TROUBLE CODE DEFINITIONS in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article.

Note. For location of components, see COMPONENT LOCATIONS .

CAMSHAFT POSITION SENSOR

Manufacturer does not provide testing procedures for many individual systems and components. A malfunction in Camshaft Position (CMP) sensor circuit can set a DTC. For testing procedures and specifications, perform related DTC testing procedure. See DIAGNOSTIC TROUBLE CODE DEFINITIONS in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article.

CRANKSHAFT POSITION SENSOR

Manufacturer does not provide testing procedures for many individual systems and components. A malfunction in Crankshaft Position (CKP) sensor circuit can set a DTC. For testing procedures and specifications, perform related DTC testing procedure. See DIAGNOSTIC TROUBLE CODE DEFINITIONS in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article.

EGR POSITION SENSOR

Manufacturer does not provide testing procedures for many individual systems and components. A malfunction in Exhaust Gas Recirculation (EGR) position sensor circuit can set a DTC. For testing procedures and specifications, perform related DTC testing procedure. See DIAGNOSTIC TROUBLE CODE DEFINITIONS in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article.

ENGINE COOLANT TEMPERATURE SENSOR

1. Manufacturer does not provide testing procedures for many individual systems and components. A malfunction in Engine Coolant Temperature (ECT) sensor circuit can set a DTC. For testing procedures and specifications, perform related DTC testing procedure. 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. An out-of-calibration ECT sensor may not set a DTC. Use the following procedure to test sensor calibration.
2. Disconnect ECT sensor harness connector. Using DVOM, measure resistance between terminals of ECT sensor at specified temperatures. See «TEMPERATURE VS. RESISTANCE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) table. Resistance should be high when engine is cold and drop as engine warms. With vehicle sitting overnight, IAT sensor and ECT sensor should have close to the same resistance reading. If resistance is not within specification, replace ECT sensor.

TEMPERATURE VS. RESISTANCE

FUEL LEVEL SENSOR

Manufacturer does not provide testing procedures for many individual systems and components. The PCM monitors the fuel level input for various diagnostics. A malfunction in fuel level sensor circuit can set a DTC. For testing procedures and specifications, perform related DTC testing procedure. See DIAGNOSTIC TROUBLE CODE DEFINITIONS in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article.

FUEL TANK PRESSURE SENSOR

Manufacturer does not provide testing procedures for many individual systems and components. A malfunction in Fuel Tank Pressure (FTP) sensor circuit can set a DTC. For testing procedures and specifications, perform related DTC testing procedure. See DIAGNOSTIC TROUBLE CODE DEFINITIONS in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article.

HEATED OXYGEN SENSOR

Manufacturer does not provide testing procedures for many individual systems and components. A malfunction in Heated Oxygen (HO2S) sensor circuit can set a DTC. For testing procedures and specifications, perform related DTC testing procedure. See DIAGNOSTIC TROUBLE CODE DEFINITIONS in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article.

INTAKE AIR TEMPERATURE SENSOR

1. Manufacturer does not provide testing procedures for many individual systems and components. A malfunction in Intake Air Temperature (IAT) sensor circuit can set a DTC. For testing procedures and specifications, perform related DTC testing procedure. 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. An out-of-calibration IAT sensor may not set a DTC. Use the following procedure to test sensor calibration.
2. Disconnect IAT sensor harness connector. (Scheme 84) Using DVOM, measure resistance between terminals of IAT sensor at specified temperatures. See «TEMPERATURE VS. RESISTANCE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) table. Resistance should be high when air temperature is cold and drop as air temperature warms. With vehicle sitting overnight, ECT sensor and IAT sensor should have close to the same resistance reading. If resistance is not within specification, replace IAT sensor.

Scheme 84

KNOCK SENSOR

Manufacturer does not provide testing procedures for many individual systems and components. A malfunction in Knock Sensor (KS) circuit can set a DTC. For testing procedures and specifications, perform related DTC testing procedure. See DIAGNOSTIC TROUBLE CODE DEFINITIONS in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article.

Description

The Manifold Absolute Pressure (MAP) sensor responds to pressure changes in the intake manifold which gives an indication of the engine load. The MAP sensor has the following circuits

1. A 5-volt reference circuit.
2. A low reference circuit.
3. MAP sensor signal circuit.

The Powertrain Control Module (PCM) supplies 5 volts to the MAP sensor on the 5-volt reference circuit and provides a ground on the low reference circuit. The MAP sensor provides a signal to the PCM on the signal circuit which is relative to the pressure changes in the manifold. With low MAP such as during idle or deceleration, the PCM should detect a low signal voltage. With high MAP such as ignition ON, with the engine OFF or Wide Open Throttle (WOT), the PCM should detect a high signal voltage. Certain vehicle models will also use the MAP sensor to calculate the Barometric (BARO) pressure when the ignition switch is turned to RUN position, with the engine OFF. The BARO reading may also be updated whenever the engine is operated at WOT. The PCM monitors the MAP sensor signal for voltage outside of the normal range. If the PCM detects a MAP sensor signal voltage that is excessively high, DTC P0108 will set. If the PCM detects a MAP sensor signal voltage that is excessively low, DTC P0107 will set.

Test Description

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

1. 4 - This step tests the MAP sensor's ability to correctly indicate BARO.

Diagnostic Procedure

1. Perform Diagnostic System Check - Engine Controls. See «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. After performing Diagnostic System Check - Engine Controls, go to next step.
2. Check for the following conditions: Vacuum hoses disconnected, damaged, or incorrectly routed. MAP sensor vacuum hose damage. Restrictions in the MAP sensor vacuum source. Intake manifold vacuum leaks. Did you find and correct the condition? If yes, go to step 24 . If no, go to next step.
3. Do you have access to another vehicle in which the MAP sensor pressure can be observed using a scan tool? If yes, go to next step. If no, go to step 5 .
4. Turn ignition switch to OFF position. Observe the MAP sensor pressure using a scan tool. Observe the MAP sensor pressure in the known good vehicle using a scan tool. Compare the values. Is the difference between the values less than .44 psi (3 kPa)? If yes, go to next step. If no, go to step 10 .
5. Turn ignition switch to RUN position, engine OFF. Observe the MAP sensor pressure using a scan tool. See «ALTITUDE VS. BAROMETRIC PRESSURE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) table. The MAP sensor pressure should be within the range specified for your altitude. Does the MAP sensor indicate the correct barometric pressure? If yes, go to next step. If no, go to step 10 .
6. Observe the MAP sensor pressure using a scan tool. Start the engine. Does the MAP sensor pressure change? If yes, go to next step. If no, go to step 10 .
7. Turn ignition switch to OFF position. Remove the MAP sensor from the engine vacuum source. Leave the MAP sensor connected to the engine harness. Connect a hand vacuum pump to the MAP sensor. Turn ignition switch to RUN position, engine OFF. Observe the MAP sensor pressure using the scan tool. Apply vacuum to the MAP sensor using the hand vacuum pump in one in. Hg increments until 15 in. Hg is reached. Each one in. Hg should decrease MAP sensor pressure by .44-.58 psi (3-4 kPa). Is the decrease in MAP sensor pressure consistent? If yes, go to next step. If no, go to step 20 .
8. Apply vacuum using the hand vacuum pump until 20 in. Hg is reached. Is the MAP sensor pressure less than 4.93 psi (34 kPa)? If yes, go to next step. If no, go to step 10 .
9. Disconnect the hand vacuum pump from the MAP sensor. Does the MAP sensor pressure return to the value observed in step No. 4 or 5? If yes, system is okay at this time. If no, go to step 22 .
10. Disconnect the MAP sensor harness connector. Observe the MAP sensor parameter using the scan tool. Is the voltage less than 0.1 volt? If yes, go to next step. If no, go to step 15 .
11. Measure the voltage from the MAP sensor 5 volt reference circuit to a good ground using a DVOM. Is the voltage more than 5.2 volts? If yes, go to step 16 . If no, go to next step.
12. Probe the MAP sensor 5-volt reference circuit using a test light connected to a good ground. Is the test light OFF? If yes, go to step 17 . If no, go to next step.
13. Connect a 3-amp fused jumper wire between the MAP sensor 5-volt reference circuit and the MAP sensor signal circuit. Observe the MAP sensor parameter using the scan tool. Is the voltage more than 4.9 volts? If yes, go to next step. If no, go to step 18 .
14. Turn ignition switch to OFF position. Remove the jumper wire. Disconnect the Engine Coolant Temperature (ECT) sensor harness connector. Connect a jumper wire between each of the MAP sensor harness connector terminals and the corresponding terminal at the MAP sensor. Turn ignition switch to RUN position, engine OFF. Measure the voltage from the MAP sensor low reference circuit at the jumper wire terminal to a good ground using a DVOM. Is the voltage more than 0.2 volt? If yes, go to step 19 . If no, go to step 20 .
15. Test the MAP sensor signal circuit between the PCM and the MAP sensor for a short to voltage. Did you find and correct the condition? If yes, go to step 24 . If no, go to step 23 .
16. Test all the branches of the 5-volt reference circuit that are shared with the MAP sensor for a short to voltage. Did you find and correct the condition? If yes, go to step 24 . If no, go to step 23 .
17. Test the 5-volt reference circuit between the PCM and the MAP sensor for an open or for a high resistance. Did you find and correct the condition? If yes, go to step 24 . If no, go to step 21 .
18. Test the MAP sensor signal circuit between the PCM and the MAP sensor for the following: A short to ground. An open. High resistance. Did you find and correct the condition? If yes, go to step 24 . If no, go to step 21 .
19. Test the low reference circuit between the PCM and the MAP sensor for an open or for high resistance. Did you find and correct the condition? If yes, go to step 24 . If no, go to step 21 .
20. Test for an intermittent and for a poor connection at the MAP sensor. Did you find and correct the condition? If yes, go to step 24 . If no, go to next step.
21. Test for an intermittent and for a poor connection at the PCM. Did you find and correct the condition? If yes, go to step 24 . If no, go to step 23 .
22. Replace the MAP sensor. After repair, go to step 24 .
23. Replace PCM. Program replacement PCM. 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.
24. Use the scan tool to clear the DTCs that may have set. Turn OFF the ignition for 30 seconds. Start the engine. Did you correct the condition? If yes, system is okay. If no, go to step 2 .

ALTITUDE VS. BAROMETRIC PRESSURE (1)

THROTTLE POSITION SENSOR

Note. Throttle Position (TP) sensor is not adjustable. Replace TP sensor as necessary.

Manufacturer does not provide testing procedures for many individual systems and components. A malfunction in TP sensor circuit can set a DTC. For testing procedures and specifications, perform related DTC testing procedure. See DIAGNOSTIC TROUBLE CODE DEFINITIONS in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article.

TRANSAXLE RANGE SWITCH

See appropriate DIAGNOSIS article in AUTOMATIC TRANSMISSIONS.

VEHICLE SPEED SENSOR

See appropriate DIAGNOSIS article in AUTOMATIC TRANSMISSIONS.

RELAYS & SOLENOIDS

Note. Manufacturer does not provide testing procedures for many individual systems and components. For module, relay and solenoid testing not listed, perform related DTC testing procedure. See DIAGNOSTIC TROUBLE CODE DEFINITIONS in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article.

Note. For location of components, see COMPONENT LOCATIONS .

A/C COMPRESSOR CLUTCH RELAY

See appropriate AUTOMATIC A/C-HEATER SYSTEMS or MANUAL A/C-HEATER SYSTEMS article in AIR CONDITIONING & HEATING.

FUEL PUMP RELAY

Manufacturer does not provide testing procedures for many individual systems and components. For fuel pump relay diagnostics, see FUEL SYSTEM DIAGNOSIS under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 3.1L CENTURY, GRAND PRIX & MALIBU article.

IDLE AIR CONTROL VALVE

See IDLE CONTROL SYSTEMS .

IGNITION RELAY DIAGNOSIS

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

Note. Manufacturer does not provide testing for all individual systems and components. For ignition relay diagnosis for Malibu, see ELECTRONIC IGNITION SYSTEM DIAGNOSIS under IGNITION SYSTEMS.

Circuit Description

The ignition relay is a normally open relay. The relay armature is held in the open position by spring tension. When the ignition switch is turned to the run or start position, current will flow through the relay coil. A wire connected to the other end of the relay coil completes the path to ground. The electromagnetic field created by the relay coil, overcomes the spring tension and moves the armature allowing the relay contacts to close. The closed relay contacts allow current to flow from the battery to the following fuses

Century

1. OXY SEN
2. ELEK IGN
3. F/INJR
4. TRANS
5. ENG EMIS

Grand Prix

1. INJ
2. IGN 1 UH
3. ELEK IGN
4. TCC
5. A/C CLU/ABS IGN

When the ignition switch is turned to the OFF position, the electromagnetic field collapses. This action allows the spring tension to move the armature away from the relay contacts, which interrupts current flow to the fuses. If the ignition relay fails to close, the engine will crank, but will not run. The class 2 communications will be available with the use of a scan tool.

Note. The ignition relay diagnostic procedure assumes that the vehicle battery is fully charged.

1. Perform Diagnostic System Check - Engine Controls. See «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. After performing diagnostic system check - engine controls, go to next step.
2. Turn ignition switch to RUN position, engine OFF. Remove the underhood junction block cover. Probe the following fuses using a test light connected to a good ground: Century OXY SEN ELEK IGN F/INJR TRANS ENG EMIS Grand Prix INJ IGN 1 UH ELEK IGN TCC A/C CLU/ABS IGN Does the test light illuminate on at least one test point of each fuse? If yes, go to next step. If no, go to step 11.
3. Turn ignition switch to OFF position. Probe both test points of the A/C ENG EMIS (Century) or CLU/ABS IGN (Grand Prix) fuse using a test light connected to a good ground. Does the test light illuminate on either test point of the fuse? If yes, go to next step. If no, go to step 36.
4. Turn ignition switch to OFF position. Remove the ignition relay from the underhood junction block using Relay Puller Pliers (J 43244). (Scheme 85) Probe both test points of the PCM-BCM fuse (Century) or ECM fuse (10-amp) in the Instrument Panel (IP) fuse block using a test light connected to a good ground. See «WIRING DIAGRAMS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l). Does the test light illuminate on any of the fuse test points? If yes, go to step 8. If no, go to next step.
5. Test the ignition relay load circuit bus bar of the underhood junction block between the ignition relay and the fuses to the circuit components for a short to battery positive voltage. Did you find a condition? If yes, go to step 35. If no, go to next step.
6. Remove the following fuses from the underhood junction block. See «WIRING DIAGRAMS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l). Century OXY SEN ELEK IGN F/INJR TRANS ENG EMIS Grand Prix INJ IGN 1 UH ELEK IGN TCC A/C CLU/ABS IGN Probe all these fuse terminals in the underhood junction block using a test light connected to a good ground. Does the test light illuminate at any of the fuse terminals? If yes, go to next step. If no, go to step 32.
7. Remove the A/C clutch relay from the underhood junction block using the relay puller pliers. Probe both fuse terminals of the ENG EMISS (Century) or A/C CLU/ABS IGN (Grand Prix) fuse in the underhood junction block using a test light connected to a good ground. Does the test light illuminate on either fuse terminal? If yes, diagnose engine electrical system. See ENGINE ELECTRICAL DIAGNOSTIC SYSTEM CHECK under SELF-DIAGNOSTIC SYSTEM in appropriate GENERATORS & REGULATORS article. If no, go to step 34.
8. Disconnect the ignition switch harness connector. Connect a 20-amp fused jumper wire from the ignition switch connector battery positive voltage terminal to the corresponding terminal at the vehicle harness connector. Probe the ignition 1 voltage circuit at the ignition switch harness connector with a test light connected to a good ground. Does the test light illuminate? If yes, go to step 30. If no, go to next step.
9. Remove the following fuses from the I/P fuse block. See «WIRING DIAGRAMS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l). Century TURN SIGNALS, CORN LPS AIR BAG CLUSTER PCM, BCM, U/H RELAY Grand Prix TURN SIR (Air Bag) IP-IGN CRUISE PCM Probe the ignition switch harness connector ignition 1 voltage circuit that leads to the I/P fuse block, using a test light connected to a good ground. Does the test light illuminate? If yes, go to step 30. If no, go to next step.
10. Disconnect the underhood junction block harness connector that contains the ignition relay ignition 1 voltage circuit. Probe the ignition relay ignition 1 voltage circuit at the underhood junction block vehicle harness connector using a test light connected to a good ground. Does the test light illuminate? If yes, go to step 31. If no, go to step 35.
11. Turn ignition switch to OFF position. Probe both test points of the 30-amp IGN 1 fuse in the underhood junction block using a test light connected to a good ground. Does the test light illuminate on both test points of the fuse? If yes, go to step 15. If no, go to next step.
12. Does the test light illuminate on one test point of the 30-amp IGN 1 fuse? If yes, go to next step. If no, go to step 21.
13. Test the battery positive voltage circuit between the underhood junction block and the ignition switch for a short to ground. Did you find and correct the condition? If yes, go to step 36. If no, go to next step.
14. Test the ignition 1 voltage circuit between the ignition switch and the 10-amp PCM, BCM, U/H relay (Century) or 10-amp ECM fuse (Grand Prix) terminals in the I/P fuse block for a short to ground. Did you find and correct the condition? If yes, go to step 36. If no, go to step 33.
15. Turn ignition switch to RUN position, engine OFF. Probe both test points of the 10-amp ECM fuse using a test light connected to a good ground. Does the test light illuminate on both test point of the fuse? If yes, go to step 22. If no, go to next step.
16. Does the test light illuminate on one test point of the 10-amp PCM, BCM, U/H relay (Century) 10-amp ECM fuse (Grand Prix)? If yes, go to step 19. If no, go to next step.
17. Test the ignition 1 voltage circuit between the ignition switch and the PCM, BCM, U/H relay (Century) 10-amp ECM fuse (Grand Prix) for a high resistance or for an open. Did you find and correct the condition? If yes, go to step 36. If no, go to next step.
18. Test the battery positive voltage circuit between the underhood junction block and the ignition switch for a high resistance or for an open. Did you find and correct the condition? If yes, go to step 36. If no, go to step 33.
19. Test the ignition 1 voltage circuit between the I/P fuse block and the underhood junction block for a short to ground. Did you find and correct the condition? If yes, go to step 36. If no, go to next step.
20. Test the underhood junction block, ignition 1 voltage bus bar circuit to the ignition relay for a short to ground. Did you find a condition? If yes, go to step 35. If no, go to step 32.
21. Turn ignition switch to OFF position. Probe the mounting stud for the battery positive cable at the underhood junction block using a test light connected to a good ground. Does the test light illuminate? If yes, go to step 35. If no, diagnose engine electrical system. See ENGINE ELECTRICAL DIAGNOSTIC SYSTEM CHECK under SELF-DIAGNOSTIC SYSTEM in appropriate GENERATORS & REGULATORS article.
22. Turn ignition switch to OFF position. Remove the ignition relay using the relay puller pliers, from the underhood junction block. Probe the ignition relay battery positive voltage circuit at the underhood junction block 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 35.
23. Turn ignition switch to RUN position, engine OFF. Probe the ignition relay ignition 1 voltage circuit at the underhood junction block using a test light connected to a good ground. Does the test light illuminate? If yes, go to step 25. If no, go to next step.
24. Test the ignition 1 voltage circuit between the I/P fuse block and the underhood junction block for a high resistance or for an open. Did you find and correct the condition? If yes, go to step 36. If no, go to step 35.
25. Turn ignition switch to RUN position, engine OFF. Probe the ignition relay coil ground circuit at the underhood junction block using a test light connected to battery voltage. Does the test light illuminate? If yes, go to step 27. If no, go to next step.
26. Turn ignition switch to OFF position. Disconnect the negative battery cable at the battery. Disconnect the underhood junction block harness connector that contains the relay coil ground circuit. Test the ignition relay coil ground circuit at the underhood junction block harness connector for a high resistance or for an open. Did you find and correct the condition? If yes, go to step 36. If no, go to step 35.
27. Turn ignition switch to OFF position. Jumper the ignition relay battery positive voltage circuit and the ignition relay load circuit together at the underhood junction block using a 20-amp fused jumper wire. Probe the following fuses using a test light connected to a good ground. See «WIRING DIAGRAMS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l). Century OXY SEN ELEK IGN F/INJR TRANS ENG EMIS Grand Prix INJ IGN 1 UH ELEK IGN TCC A/C CLU/ABS IGN Does the test light illuminate on at least one test point of each fuse? If yes, go to next step. If no, go to step 35.
28. Remove the A/C clutch relay from the underhood junction block using the relay puller pliers. Probe the A/C clutch relay ignition 1 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 35.
29. Test for an intermittent and for a poor connection at the underhood junction block, ignition relay connector location. Did you find a condition? If yes, go to step 35. If no, go to step 32.
30. Repair the short to battery positive voltage in the ignition 1 voltage circuit between the ignition switch and the I/P fuse block. After repair, go to step 36.
31. Repair the short to battery positive voltage in the ignition 1 voltage circuit between the I/P fuse block and the underhood junction block harness connector. After repair, go to step 36.
32. Replace the ignition relay. After repair, go to step 36.
33. Replace the ignition switch. After repair, go to step 36.
34. Replace the A/C clutch relay. After repair, go to step 36.
35. Replace the underhood junction block. After repair, go to next step.
36. Replace any open fuses. Turn ignition switch to OFF position for 30 seconds. Attempt to start the engine. Does the engine start and run? If yes, go to next step. If no, diagnose no start condition. Go to «NO-START DIAGNOSIS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-31l__no-start-diagnosis) in BASIC DIAGNOSTIC PROCEDURES - 3.1L CENTURY, GRAND PRIX & MALIBU article.
37. Clear the DTCs using a scan tool. Operate the vehicle for 5 minutes. Does a DTC set during this ignition cycle? If yes, go to «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.

Scheme 85

Scheme 86

FUEL SYSTEMS

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

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

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

FUEL SYSTEM PRESSURE RELEASE

1. Disconnect the negative battery cable.
2. Install the Fuel Pressure Gauge Fitting (J 34730-262) to the fuel pressure connection.
3. Connect Fuel Pressure Gauge (J 34730-1A) to the fuel pressure gauge fitting. (Scheme 87) 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.

Scheme 87

FUEL DELIVERY

Note. See FUEL SYSTEM DIAGNOSIS under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 3.1L CENTURY, GRAND PRIX & MALIBU article.

Fuel Pump Circuit

Manufacturer does not provide testing procedures for many individual systems and components. See FUEL PUMP ELECTRICAL CIRCUIT DIAGNOSIS under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 3.1L CENTURY, GRAND PRIX & MALIBU article.

Fuel Pressure Regulator

Manufacturer does not provide testing procedures for many individual systems and components. See FUEL SYSTEM DIAGNOSIS under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 3.1L CENTURY, GRAND PRIX & MALIBU article.

Water contamination in the fuel system may cause driveability conditions such as hesitation, stalling, no start, or misfires in one or more cylinders. Water may collect near a single fuel injector, at the lowest point in the fuel rail, and cause a misfire in that cylinder. If the fuel system is contaminated with water, inspect the fuel system components for rust, or deterioration.

Alcohol concentrations of 10 percent or greater in fuel can be detrimental to fuel system components. Alcohol contamination may cause fuel system corrosion, deterioration of rubber components, and subsequent fuel filter restriction. Fuel contaminated with alcohol may cause driveability conditions such as hesitation, lack of power, stalling, or no start. Some types of alcohol are more detrimental to fuel system components than others.

The fuel sample should be drawn from the bottom of the tank so that any water present in the tank will be detected. The sample should be bright and clear. If alcohol contamination is suspected then use the following procedure to test the fuel quality.

1. Using a 100 ml specified cylinder with 1 ml graduation marks, fill the cylinder with fuel to the 90 ml mark.
2. Add 10 ml of water to bring the total fluid volume to 100 ml and install a stopper.
3. Shake the cylinder vigorously for 10-15 seconds.
4. Carefully loosen the stopper to release the pressure.
5. Re-install the stopper and shake the cylinder vigorously again for 10-15 seconds.
6. Put the cylinder on a level surface for about 5 minutes to allow adequate liquid separation.

If alcohol is present in the fuel, the volume of the lower layer, which would now contain both alcohol and water, will be more than 10 ml. For example, if the volume of the lower layer is increased to 15 ml, this indicates at least 5 percent alcohol in the fuel. The actual amount of alcohol may be somewhat more because this procedure does not extract all of the alcohol from the fuel.

Particulate Contaminants In Fuel Testing Procedure

The fuel sample should be drawn from the bottom of the tank so that any water present in the tank will be detected. The sample should be bright and clear. If the sample appears cloudy, or contaminated with water, as indicated by a water layer at the bottom of the sample, use the following procedure to diagnose the fuel.

1. Using an approved fuel container, draw about 0.5 liter of fuel.
2. Place the cylinder on a level surface for about 5 minutes to allow settling of the particulate contamination.

Particulate contamination will show up in various shapes and colors. Sand will typically be identified by White or Light Brown crystals. Rubber will appear as Black and irregular particles. If particles are found, clean the entire fuel system thoroughly. See FUEL SYSTEM CLEANING .

Fuel quality can affect vehicle performance. Gasoline and gasoline blends that are contaminated or contain excessive amounts of alcohol can affect vehicle driveability, fuel economy, fuel system components, and emissions. Excessive alcohol in the fuel may cause fuel system corrosion, deterioration of rubber components, and subsequent fuel filter restriction. Some types of alcohol are more detrimental to fuel system components than others. Ethanol is commonly used in gasoline, but in concentrations of no more than 10 percent. Some fuels, such as E85, contain a very high percent of ethanol. Fuel with more than 10 percent ethanol may cause driveability conditions in vehicles such as hesitation, lack of power, stalling, or no start. If excessive alcohol in the fuel is suspected, then use the following procedure to test the fuel quality.

Note. Numbers in parenthesis in the following steps correspond to numbered components in referenced figures.

1. Turn ON the Fuel Composition Tester (J 44175), or equivalent.
2. Verify the fuel composition tester is operational by measuring the AC frequency output using a DVOM. A frequency without a fuel sample in the test cell indicates that the tester is working correctly.
3. Install Fuel Pressure Gauge (J 34730-1A).
4. Close the fuel pressure gauge bleed valve.
5. Place the bleed hose (1) of the fuel pressure gauge into the 100 ml beaker (2). (Scheme 88)
6. Command the fuel pump relay ON using a scan tool.
7. Slowly open the bleed valve on the fuel pressure gauge, until an adequate fuel sample is obtained.
8. If water appears in the fuel sample, clean the fuel system and replace the fuel in the vehicle. See «FUEL SYSTEM CLEANING»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l__fuel-system-cleaning).
9. Pour the fuel sample from the beaker (1) into the fuel composition tester, until the level of the fuel is at the top of each fuel test port (2). (Scheme 89)
10. Observe the diagnostic LEDs on the fuel composition tester. If the Red fuel diagnostic LED is illuminated, a fuel contamination condition exists. See «FUEL SYSTEM CLEANING»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l__fuel-system-cleaning).
11. Measure the output frequency of the fuel composition tester.
12. Subtract 50 from the reading on the DVOM to obtain the percentage of alcohol in the fuel sample. See examples in «FUEL COMPOSITION TEST EXAMPLES»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) table.
13. If the fuel sample contains more than 10 percent ethanol, replace the fuel in the vehicle.
14. Check for particulates in fuel. See «PARTICULATE CONTAMINANTS IN FUEL TESTING PROCEDURE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l__particulate-contaminants-in-fuel-testing-procedure).

FUEL COMPOSITION TEST EXAMPLES

Scheme 88

Scheme 89

The scan tool is first used to energize the fuel pump relay. The fuel injector tester is then used to pulse each injector for a precise amount of time, allowing a measured amount of fuel into the manifold. This causes a drop in system fuel pressure that can be recorded and used to compare each injector. See FUEL INJECTOR BALANCE TEST EXAMPLE (TYPICAL) table.

FUEL INJECTOR BALANCE TEST EXAMPLE (TYPICAL)

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

1. 3 - Engine Coolant Temperature (ECT) must be below the operating temperature to avoid irregular fuel pressure readings due to hot soak fuel boiling.
2. 6 - If the pressure drop value for each fuel injector is within 1.5 psi (10 kPa) of the average pressure drop value, the fuel injectors are flowing properly.

1. Perform Diagnostic System Check - Engine Controls. See «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. After performing diagnostic system check - engine controls, go to next step.
2. Did you perform the Fuel Injector Coil Test? If yes, go to next step. If no, go to «FUEL INJECTOR COIL TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l).
3. Observe the ECT parameter on the scan tool. Does the scan tool indicate that the ECT parameter is less than 201°F (94°C)? If yes, go to next step. If no, allow engine to cool below 201°F (94°C), then go to next step.
4. Turn ignition switch to OFF position. Turn OFF all accessories. Install Fuel Pressure Gauge (J 34730-A), or equivalent. Turn ignition switch to RUN position, engine OFF. Command the fuel pump ON using a scan tool. The fuel pump may need to be commanded ON a few times to obtain the highest possible fuel pressure. DO NOT start the engine. Observe the fuel pressure gauge, with the fuel pump commanded ON. Is the fuel pressure 52-59 psi (358-407 kPa)? If yes, go to next step. If no, 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.
5. Monitor the fuel pressure gauge for one minute. Does the fuel pressure decrease by more than 5 psi (34 kPa)? If yes, 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. If no, go to next step.
6. Connect the Fuel Injector Coil/Balancer Tester (J 39021), Injector Selector Switch Box (J 39021-210), and Fuel Injector Harness Adapter (J 39021-410), or equivalents, to the fuel injector multi-way connector. Set the amperage supply selector switch on the fuel injector tester to the balance test 0.5-2.5 AMP position. Command the fuel pump relay ON and then OFF using a scan tool. Record the fuel pressure indicated by the Fuel Pressure Gauge (J 34730-1A), or equivalent, after the fuel pressure stabilizes. This is the first pressure reading. (Scheme 90) Record the fuel pressure value immediately after the fuel injector stops pulsing. The fuel pressure may rise after the fuel injector stops pulsing. Do not record the higher fuel pressure value. Energize the fuel injector by depressing the PUSH TO START TEST button on the fuel injector tester. Record the fuel pressure indicated by the fuel pressure gauge. This is the second fuel pressure reading. Repeat procedure for each fuel injector. Subtract the second pressure reading from the first pressure reading for one fuel injector. The result is the pressure drop value. Obtain a pressure drop value for each fuel injector. Add all of the individual pressure drop values. This is the total pressure drop. Divide the total pressure drop by the number of fuel injectors. This is the average pressure drop. Does any fuel injector have a pressure drop value that is more than the average pressure drop or less than the average pressure drop by 1.5 psi (10 kPa)? If yes, go to next step. If no, diagnose by symptom. See «SYMPTOMS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__symptoms) in TROUBLE SHOOTING - NO CODES - 3.1L CENTURY, GRAND PRIX & MALIBU article.
7. Clean the fuel injector. See «FUEL INJECTOR CLEANING»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l__fuel-injector-cleaning). After repair, go to next step.
8. Operate the system to verify the repair. Did you correct the condition? If yes, system is okay at this time. If no, diagnose by symptom. See «SYMPTOMS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__symptoms) in TROUBLE SHOOTING - NO CODES - 3.1L CENTURY, GRAND PRIX & MALIBU article.

Scheme 90

The scan tool first energizes the fuel pump and then the fuel injectors for a precise amount of time allowing a measured amount of fuel into the manifold. This causes a drop in system fuel pressure that can be recorded and used to compare each injector.

The number below refers to the step number in the diagnostic procedures.

1. 3 -The Engine Coolant Temperature (ECT) must be below the operating temperature to avoid irregular fuel pressure readings due to hot soak fuel boiling.

1. Perform Diagnostic System Check - Engine Controls. See «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. After performing diagnostic system check - engine controls, go to next step.
2. Did you perform the Fuel Injector Coil Test? If yes, go to next step. If no, go to «FUEL INJECTOR COIL TEST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) .
3. Observe the ECT sensor parameter using a scan tool. Does the scan tool indicate that the ECT parameter is less than 201°F (94°C)? If yes, go to next step. If no, allow engine to cool below 201°F (94°C), then go to next step.
4. Turn ignition switch to OFF position. Turn OFF all accessories. Install Fuel Pressure Gauge (J 34730-A), or equivalent. Turn ignition switch to RUN position, engine OFF. Command the fuel pump ON, using a scan tool. The fuel pump may need to be commanded ON a few times to obtain the highest possible fuel pressure. DO NOT start the engine. Observe the fuel pressure gauge, with the fuel pump commanded ON. Is the fuel pressure 52-59 psi (358-407 kPa)? If yes, go to next step. If no, 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.
5. Monitor the fuel pressure gauge for one minute. Does the fuel pressure decrease by more than 5 psi (34 kPa)? If yes, 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. If no, go to next step.
6. Using a scan tool, select the FUEL INJECTOR BALANCE TEST function, within the SPECIAL FUNCTIONS menu. Select a fuel injector to be tested. Press ENTER to prime the fuel system. Record the fuel pressure indicated by the fuel pressure gauge after the fuel pressure stabilizes. This is the first pressure reading. Record the fuel pressure value immediately after the fuel injector stops pulsing. The fuel pressure may rise after the fuel injector stops pulsing. Do not record the higher fuel pressure value. Energize the fuel injector by depressing the PULSE INJECTOR button on the scan tool. This energizes the fuel injector and decreases the fuel pressure. Record the fuel pressure indicated by the fuel pressure gauge after the fuel injector has stopped pulsing. This is the second pressure reading. Press ENTER again to bring you back to the SELECT INJECTOR screen. Repeat for each fuel injector. Subtract the second pressure reading from the first pressure reading for one fuel injector. The result is the pressure drop value. Obtain a pressure drop value for each fuel injector. Add all of the individual pressure drop values. This is the total pressure drop. Divide the total pressure drop by the number of fuel injectors. This is the average pressure drop. Does any fuel injector have a pressure drop value that is either higher than the average pressure drop or lower than the average pressure drop by more than 1.5 psi (10 kPa)? If yes, go to next step. If no, diagnose by symptom. See «SYMPTOMS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__symptoms) in TROUBLE SHOOTING - NO CODES - 3.1L CENTURY, GRAND PRIX & MALIBU article.
7. Clean the fuel injector. See «FUEL INJECTOR CLEANING»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l__fuel-injector-cleaning) . After repair, go to next step.
8. Operate the vehicle to verify the repair. Did you correct the condition? If yes, system is okay at this time. If no, diagnose by symptom. See «SYMPTOMS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__symptoms) in TROUBLE SHOOTING - NO CODES - 3.1L CENTURY, GRAND PRIX & MALIBU article.

The Powertrain Control Module (PCM) enables the appropriate fuel injector on the intake stroke for each cylinder. A voltage is supplied directly to the fuel injectors. The PCM controls each fuel injector by grounding the control circuit via a solid state device called a driver. A fuel injector coil winding resistance that is too high, or low, will affect engine driveability. A fuel injector control circuit DTC may not set, but a misfire may be apparent. The fuel injector coil windings are affected by temperature. The resistance of the fuel injector coil windings will increase as the temperature of the fuel injector increases.

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

1. 3 - This step tests each fuel injector resistance within a specific temperature range. If any of the fuel injectors display a resistance outside of the specified value, replace the fuel injector.
2. 4 - This step determines if all of the fuel injectors are within 3 ohms of each other. If the highest resistance value is within 3 ohms of the lowest resistance value, then all of the fuel injector coil windings are okay.
3. 5 - This step determines which fuel injector is faulty. After subtracting the highest and lowest resistance values from the average value, replace the fuel injector that has the greatest resistance difference from the average.

1. Perform Diagnostic System Check - Engine Controls. See «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. After performing diagnostic system check - engine controls, go to next step.
2. Using scan tool, check Engine Coolant Temperature (ECT) sensor value. Is the ECT sensor value 50-90°F (10-32°C)? If yes, go to next step. If no, go to step 4.
3. Disconnect fuel injector harness connector. Using a DVOM, measure the resistance of each fuel injector between the ignition feed circuit and the fuel injector control circuit, at the multi-way harness connector. (Scheme 91) Do any of the fuel injectors display a resistance outside 11-14 ohms? If yes, go to next step. If no, go to «DIAGNOSTIC AIDS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l__diagnostic-aids).
4. Disconnect the fuel injector multi-way harness connector. Using a DVOM, measure the resistance of each fuel injector between the ignition feed circuit and the fuel injector control circuit, at the multi-way harness connector. (Scheme 91) Record each fuel injector value. Subtract the lowest resistance value from the highest resistance value. Is the difference equal to, or less than 3 ohms? If yes, go to «FUEL INJECTOR BALANCE TEST WITH SPECIAL TOOL»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) or «FUEL INJECTOR BALANCE TEST WITH TECH 2»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l). If no, go to next step.
5. Add all fuel injector resistance values to obtain a total resistance value. Divide the total resistance value by the number of fuel injectors, to obtain an average resistance value. Subtract the lowest and the highest individual fuel injector resistance values from the average resistance value. Replace the fuel injector that displays the greatest resistance difference, above or below the average. After repair, go to step 7.
6. Replace the fuel injector or fuel injectors that are out of the 11-14 ohms range. After repair, go to next step.
7. Operate system to verify repair. Did you correct the condition? If yes, system is okay at this time. If no, go to step 2.

Scheme 91

Diagnostic Aids

1. Monitoring misfire current counters, or misfire graph, may help isolate fuel injector causing condition.
2. Operating vehicle over a wide temperature range may help isolate fuel injector causing condition.
3. Perform fuel injector coil test within conditions of customers concern. A fuel injector condition may only be apparent at a certain temperature, or under certain conditions.
4. If fuel injector coil test does not isolate condition perform fuel injector balance test. See «FUEL INJECTOR BALANCE TEST WITH SPECIAL TOOL»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) or «FUEL INJECTOR BALANCE TEST WITH TECH 2»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) .

The Powertrain Control Module (PCM) enables the appropriate fuel injector on the intake stroke for each cylinder. A voltage is supplied directly to the fuel injectors. The PCM controls each fuel injector by grounding the control circuit via a solid state device called a driver.

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

1. 4 - This step tests for a short to ground on the fuel injector ignition 1 voltage supply circuit.
2. 5 - This step tests for a short to a PCM ground on the fuel injector ignition 1 voltage supply circuit.
3. 6 - This step tests for an open between the multi-way harness connector and the fuel injectors.
4. 7 - This step tests for an open or high resistance between the multi-way harness connector and the fuel injectors.

1. Perform Diagnostic System Check - Engine Controls. See «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. After performing diagnostic system check - engine controls, go to next step.
2. Are any fuel injector DTCs set? If yes, go to «DTC P0201-P0206: INJECTOR CONTROL CIRCUIT»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__dtc-p0201-p0206-injector-control-circuit) under DIAGNOSTIC TESTS in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article. If no, go to next step.
3. Check the fuel injector fuse. Is the fuel injector fuse open? If yes, go to next step. If no, go to step 6.
4. Turn ignition switch to OFF position. Disconnect the fuel injector multi-way harness connector. Probe the fuel injector ignition 1 voltage circuit, fuse side, using a test light connected to battery voltage. (Scheme 91) Does the test light illuminate? If yes, go to step 9. If no, go to next step.
5. Turn ignition switch to RUN position, engine OFF. Does the test light illuminate? If yes, go to step 13. If no, go to step 8.
6. Turn ignition switch to OFF position. Disconnect the fuel injector multi-way harness connector. Turn ignition switch to RUN position, engine OFF. Probe the fuel injector ignition 1 voltage circuit, fuse side, using a test light connected to a good ground. (Scheme 91) Does the test light illuminate? If yes, go to next step. If no, go to step 10.
7. Check for continuity between the ignition 1 voltage circuit terminal and a fuel injector terminal, at the multi-way harness connector, fuel injector side. Does the DVOM display a resistance above 5 ohms? If yes, go to step 11. If no, go to step 12.
8. Test the fuel injector ignition 1 voltage circuit, between the multi-way harness connector and the fuel injectors for a short to ground. Did you find and correct the condition? If yes, go to step 14. If no, go to «DIAGNOSTIC AIDS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l).
9. Repair the short to ground in the fuel injector ignition 1 voltage circuit. After repair, go to step 14.
10. Repair the open in the ignition 1 voltage circuit between the Underhood Bussed Electrical Center (UBEC) and the multi-way harness connector. After repair, go to step 14.
11. Repair the fuel injector ignition 1 voltage circuit for an open/high resistance, between the multi-way harness connector and the splice. After repair, go to step 14.
12. Repair the poor connection at the multi-way harness connector. After repair, go to step 14.
13. Repair the short to a PCM ground in the fuel injector ignition 1 voltage circuit. After repair, go to next step.
14. 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. Monitoring the fuel injector circuit status using a scan tool, while moving the fuel injector harness, may help isolate an intermittent condition.
2. Performing the Fuel Injector Coil test may help isolate an intermittent condition.
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 - NO CODES - 3.1L CENTURY, GRAND PRIX & MALIBU article.

Manufacturer does not provide testing procedures for many individual systems and components. For fuel pump relay diagnosis, see FUEL SYSTEM DIAGNOSIS under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 3.1L CENTURY, GRAND PRIX & MALIBU article.

FUEL INJECTOR CLEANING

Note. During this procedure you will need a total of 32.4 oz. (960 ml) of cleaning solution. That is 2 tanks of solution for the fuel injector cleaner. Other brands of tools may have a different capacity and would therefore require more or less tanks to complete the procedure. You must use all 32.4 oz. (960 ml) of solution to ensure complete injector cleaning.

Cleaning Procedure

1. Obtain Fuel Injector Cleaner (J 38500-A), or equivalent. Ensure shut-off valve at bottom of the canister is closed. (Scheme 92)
2. For US dealers, empty 2 pre-measured GM Top-Engine Cleaner containers, 0.812 oz. (24 ml) each (GM P/N 12346535), into the fuel injector cleaner.
3. For Canadian dealers, measure and dispense 1.62 oz. (48 ml) of Top-Engine Cleaner (Canadian P/N 992872), into the fuel injector cleaner.
4. If you are using any other brand of tank you will need a total of 3.24 oz. (96 ml) of Top-Engine Cleaner mixed with 29.16 oz. (864 ml) of regular unleaded gasoline.
5. Fill the injector cleaning tank with regular unleaded gasoline. Be sure to follow all additional instructions provided with the tool.
6. Electrically disable the vehicle fuel pump by removing the fuel pump relay and disconnecting the oil pressure switch harness connector, if equipped.
7. Disconnect the fuel feed and return lines at the fuel rail. Plug the fuel feed and return lines coming off the fuel rail using Fuel Line Shut-Off Adapter (J 37287), or 3/8 Fuel Line Shut-Off Adapter (J 42964-1), and 5/16 Fuel Line Shut-Off Adapter (J 42964-2), or 3/8 Fuel Line Shut-Off Adapter (J 42873-1) and 5/16 Fuel Line Shut-Off Adapter (J 42873-2) as appropriate for the fuel system.
8. Connect the fuel injector cleaner to the vehicle's fuel rail.
9. Pressurize the fuel injector cleaner to 74 psi (510 kPa).
10. Start and idle the engine until it stalls, due to lack of fuel. This should take about 15-20 minutes.
11. Disconnect fuel injector cleaner from the fuel rail.
12. Reconnect the vehicle's fuel pump relay and oil pressure switch harness connector, if equipped.
13. Remove Fuel Line Shut-Off Adapters and reconnect the vehicles fuel feed and return lines.
14. Start and idle the vehicle for an additional 2 minutes to ensure residual injector cleaner is flushed from the fuel rail and fuel lines.
15. Repeat steps 1-5 of the appropriate Injector Balance Test and record the fuel pressure drop from each injector. See «FUEL INJECTOR BALANCE TEST WITH SPECIAL TOOL»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) or «FUEL INJECTOR BALANCE TEST WITH TECH 2»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l).
16. Subtract the lowest fuel pressure drop from the highest fuel pressure drop. If the value is 2 psi (15 kPa) or less, no additional action is required. If the value is greater than 2 psi (15 kPa), replace the injector with the lowest fuel pressure drop.
17. Add one ounce of Port Fuel Injector Cleaner, (GM P/N 12345104, Canadian P/N 10953467), to the vehicles fuel tank for each gallon of gasoline estimated to be in the fuel tank. Instruct the customer to add the reminder of the bottle of Port Fuel Injector Cleaner to the vehicle fuel tank at the next fill-up.
18. Advise the customer to change brands of fuel and to add GM Port Fuel Injector Cleaner every 3000 miles. GM Port Fuel Injector Cleaner contains the same additives that the fuel companies are removing from the fuel to reduce costs. Regular use of GM Port Fuel Injector Cleaner should keep the customer from having to repeat the injector cleaning procedure.
19. Road test the vehicle to verify that the customer concern has been corrected.

Scheme 92

FUEL SYSTEM CLEANING

Note. Cap the fittings and plug the holes when servicing the fuel system to prevent dirt and other contaminants from entering the open pipes and passages. Always maintain cleanliness when servicing fuel system components.

1. Remove the fuel tank. See appropriate REMOVAL & INSTALLATION article.
2. Check the fuel strainer. Replace a contaminated strainer and inspect the fuel pump.
3. Check the fuel pump inlet for dirt and debris. If dirt and debris are found, the fuel pump needs to be replaced.
4. Flush fuel tank with hot water.
5. Pour the water out of the fuel sender assembly opening in the fuel tank. Rock the fuel tank to ensure that the removal of the water from the fuel tank is complete.
6. Allow tank to dry completely before reassembly.
7. Disconnect the fuel pipes at the fuel rail.
8. Clean the fuel pipes by applying air pressure in the opposite direction of the fuel flow.
9. Connect the fuel pipes at the fuel rail.
10. Replace the fuel filter.
11. Install the fuel sender assembly.
12. Install the fuel tank.

IDLE CONTROL SYSTEMS

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

Note. Perform powertrain diagnostic system check prior to testing, and after completing any repair. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article.

The engine idle speed is controlled by the Idle Air Control (IAC) valve. The IAC valve is on the throttle body. The IAC valve pintle moves in and out of an idle air passage bore to control air flow around the throttle plate. The valve consists of a movable pintle, driven by a gear attached to a 2 phase bi-polar permanent magnet electric motor called a stepper motor. The stepper motor is capable of highly accurate rotation, or of movement, called steps. The stepper motor has 2 separate windings that are called coils. Each coil is fed by 2 circuits from the Powertrain Control Module (PCM). When the PCM changes polarity of a coil, the stepper motor moves one step. The PCM uses a predetermined number of counts to determine the IAC pintle position. Observe IAC valve counts using a scan tool. The IAC valve counts will increment up or down as the PCM attempts to change the IAC valve pintle position. An IAC Reset will occur when the ignition key is turned OFF. First, the PCM will seat the IAC valve pintle in the idle air passage bore. Second, the PCM will retract the pintle a predetermined number of counts to allow for efficient engine start-up. If the engine idle speed is out of range for a calibrated period of time, an idle speed Diagnostic Trouble Code (DTC) may set.

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

1. 5 - This test determines the ability of the PCM and IAC valve circuits to control the IAC valve.
2. 7 - This test determines the ability of the PCM to provide the IAC valve circuits with a ground. On a normal operating system, the test light should not flash while the IAC counts are incrementing.

1. Perform Diagnostic System Check - Engine Controls. See «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.
2. Set parking brake and block drive wheels. Start engine. Turn all accessories OFF. Using scan tool RPM CONTROL function, slowly increment engine speed to 1700 RPM, then to 600 RPM. Then to 1700 RPM. Exit RPM CONTROL function. Did the engine speed stabilize within 100 RPM less than the commanded engine speed or within 150 RPM above the Commanded RPM? If yes, see «DIAGNOSTIC AIDS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) . If no, go to next step.
3. Turn ignition switch to OFF position. Disconnect IAC valve harness connector. Connect IAC Motor Driver (J 37027-1A), or equivalent, to the IAC valve. Start the engine. Using IAC system motor driver, command IAC valve in until about 600 RPM is reached and then command IAC valve out until about 1700 RPM is reached. Return engine RPM to desired idle as indicated on scan tool data list. Did the engine speed steadily decrease to near 600 RPM and steadily increase to near 1700 RPM when the IAC valve was commanded in and out? If yes, go to step 5 . If no, go to next step.
4. Did you observe an excessively high idle condition that could not be controlled using the IAC motor driver during the last test? If yes, go to step 11 . If no, go to step 12 .
5. Connect a test light between one of the IAC valve control circuits and a good ground. Start the engine. Observe the IAC Counts parameter using a scan tool. Command high RPM using the IAC motor driver until the IAC Counts parameter starts to increment. Command low RPM using the IAC motor driver until the IAC Counts parameter starts to increment. Return the engine speed to the Desired idle speed parameter. Repeat procedure for the other 3 IAC valve control circuits. Did the test light remain ON, never flashing, while the IAC Counts were incrementing for any of the IAC valve control circuits? If yes, go to step 10 . If no, go to next step.
6. Did the test light remain OFF, never flashing, while the IAC counts where incrementing at any of the IAC valve control circuits during the above test? If yes, go to step 9 . If no, go to next step.
7. Connect a test light between the IAC coil "A" low control circuit and the IAC coil "A" high control circuit. Observe the IAC Counts parameter using a scan tool and the test light. Command high RPM using the IAC motor driver until the IAC Counts parameter starts to increment. Command low RPM using the IAC motor driver until the IAC Counts parameter starts to increment. Return the Engine Speed parameter to the desired idle speed parameter. Repeat procedure with the test light connected between the IAC coil "B" low control circuit and the IAC coil "B" high control circuit. Did the test light stay illuminated, never flashing, while the IAC Counts were incrementing? If yes, go to next step. If no, go to step 17 .
8. Check for poor connection at IAC valve harness connector. Did you find and correct the condition? If yes, go to step 18 . If no, go to step 13 .
9. Turn ignition switch to OFF position. Disconnect PCM harness connectors. Using a DVOM, test the circuit where the test light remained off for the following: An open circuit. A short to ground. A short to another IAC valve control circuit. Did you find and correct the condition? If yes, go to step 18 . If no, go to step 13 .
10. Turn ignition switch to RUN position. Using a DVOM, test the circuit where the test light remained illuminated for the following: A short to voltage. A short to another IAC valve control circuit. Did you find and correct the condition? If yes, go to step 18 . If no, go to step 13 .
11. Visually and physically inspect for the following: Throttle body damage and tampering. Skewed TP sensor signal. Throttle lever screw tampering (if equipped). Vacuum leaks. Faulty, incorrectly installed PCV valve and hose (if equipped). Throttle shaft binding. Throttle linkage or cruise control linkage binding (if equipped). Remove IAC valve. Check for the following: Clogged IAC valve passage. Excessive deposits on throttle plate. Excessive deposits in throttle bore. Excessive deposits on IAC valve pintle. Did you find and correct the condition? If yes, go to step 18 . If no, go to step 15 .
12. Visually and physically check for the following: Throttle body damage and tampering. Throttle lever screw tampering (if equipped). Excessive deposits on throttle plate. Restricted air intake system. Check for possible collapsed or clogged air intake duct, before and after the air filter element, a restricted air filter element or restriction at the throttle body intake screen, if equipped. Excessive deposits in throttle bore. Remove IAC valve and inspect for excessive deposits on IAC valve pintle and in IAC valve passage. Repair as necessary. Did you find and correct the condition? If yes, go to step 18 . If no, go to step 15 .
13. Check for poor PCM harness connections. Did you find and correct the condition? If yes, go to step 18 . If no, go to next step.
14. Disconnect the PCM harness connectors. Using a DVOM, test all IAC valve circuits for high resistance. Did you find and correct the condition? If yes, go to step 18 . If no, go to step 17 .
15. Check for poor IAC valve harness connection. Did you find and correct the condition? If yes, go to step 18 . If no, go to next step.
16. Replace IAC valve. After repair, go to step 18 .
17. Replace PCM. See POWERTRAIN CONTROL MODULE under COMPUTERIZED ENGINE CONTROLS in appropriate REMOVAL & INSTALLATION article. Program PCM using correct vehicle software and 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. After repair, go to next step.
18. Reconnect any disconnected components. Use the scan tool to clear any DTCs that may have set. Turn ignition switch to OFF position for 30 seconds. Operate the vehicle within conditions to verify the repair. Did you verify the repair? If yes, go to next step. If no, go to step 2 .
19. Using a scan tool, observe the stored information in Capture Info. Does the scan tool display any DTCs that you have not diagnosed? If yes, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-self-diagnostics-31l-engine__diagnostic-trouble-code-definitions) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article. If no, system is okay at this time.

Check for the following conditions

1. High resistance in an IAC valve control circuit.
2. The correct Positive Crankcase Ventilation (PCV) valve, properly installed and proper operation of the PCV valve.
3. Proper operation and installation of all air intake components.
4. Proper installation and operation of the Mass Airflow (MAF) sensor, if equipped.
5. A tampered with or damaged throttle stop screw.
6. A tampered with or damaged throttle plate, throttle shaft, throttle linkage, or cruise control linkage, if equipped.
7. A skewed high Throttle Position (TP) sensor.
8. Excessive deposits in the IAC valve passage or on the IAC valve pintle.
9. Excessive deposits in IAC valve passage or on IAC valve pintle.
10. Excessive deposits in the throttle bore or on the throttle plate.
11. Vacuum leaks
12. A high or unstable idle condition could be caused by a non-IAC system problem that cannot be overcome by the IAC valve.
13. High or unstable idle condition caused by a non-IAC system problem that cannot be overcome by IAC valve.
14. If the problem is determined to be intermittent, see «INTERMITTENTS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-troubleshooting-no-codes-31l__intermittents) in TROUBLE SHOOTING - NO CODES - 3.1L CENTURY, GRAND PRIX & MALIBU article.

IGNITION SYSTEMS

Note. For basic ignition system checks, see appropriate BASIC DIAGNOSTIC PROCEDURES article.

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

See CAMSHAFT POSITION SENSOR under SENSORS & SWITCHES.

See CRANKSHAFT POSITION SENSOR under SENSORS & SWITCHES.

ELECTRONIC IGNITION SYSTEM DIAGNOSIS

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

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 PCM receives the second 3X signal and the PCM applies 5 volts to the IC timing signal circuit.

1. Perform Diagnostic System Check - Engine Controls. See «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.
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 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 DVOM. Is the resistance 800-1200 ohms? If yes, go to next step. If no, go to step 28 .
4. Disconnect the CKP sensor "A" harness connector located on the front of the engine near A/C compressor. Observe the 3X crank sensor parameter using a scan tool. Crank the engine. Does the scan tool indicate a 3X crank sensor signal is present? If yes, go to next step. If no, go to step 11 .
5. Connect CKP sensor "A". Check 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 ignition coils secondary resistance. Is the resistance 5-8 k/ohms? If yes, go to step 25 . If no, go to next step.
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 and inspect the 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-system-testing-engine-component-tests-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 yes, 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 circuit. 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 1 signal circuit of the CKP sensor "B" 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 1 signal circuit of the CKP sensor "B" 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 1 signal circuit and the low reference circuit of the CKP sensor "B" using the DVOM 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 the following conditions: An open. 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 the following conditions: Physical damage. Loose or improper installation. Did you find and correct the condition? If yes, 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. Replace the fuse if necessary. 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 switch 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 normal, 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 a no start condition, a start and stall condition or erratic performance.
4. An improperly installed crankshaft could cause excess crankshaft end play.

IGNITION RELAY

For ignition relay diagnosis, see IGNITION RELAY DIAGNOSIS under RELAYS & SOLENOIDS.

EMISSION SYSTEMS & SUB-SYSTEMS

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

Electric AIR Pump

Note. For AIR pump testing, perform related DTC testing procedure. See DIAGNOSTIC TROUBLE CODE DEFINITIONS in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article.

EXHAUST GAS RECIRCULATION

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

Note. For EGR system diagnosis, see INSPECTION/MAINTENANCE - EXHAUST GAS RECIRCULATION SYSTEM SET PROCEDURE in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article.

EXHAUST SYSTEM CHECK

Visual/Physical Inspection

1. Check for aftermarket or non-OEM devices such as, but not including; tailpipe extensions, headers, and exhaust cutouts. This could affect the operation and proper performance of the exhaust system.
2. Verify the exact operating conditions under which the concern exists. Note factors such as engine RPM, engine temperature, engine load, and frequency of concern.
3. Check the easily accessible or visible system components for obvious damage or conditions which could cause any symptom.

Intermittent

Test the vehicle under the same conditions that the customer reported to verify the system is operating as designed.

Symptom List

1. For loss of power, poor acceleration, poor fuel economy, excessive smoke-diesel symptoms, see «RESTRICTED EXHAUST»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l__restricted-exhaust) .
2. For exhaust hissing or popping, see «EXHAUST LEAKAGE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l__exhaust-leakage) .
3. For rattling, buzz, groan or hum or loud exhaust, see «EXHAUST NOISE»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) .

RESTRICTED EXHAUST

Note. For dual exhaust systems a quick check of exhaust flow will help determine which side of the exhaust system is restricted. The side that has less exhaust flow is the side that will be suspect, and diagnosis should begin there.

Note. For Malibu, see TEST DESCRIPTION - MALIBU .

Test Description - Century & Grand Prix

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

1. 4 - The exhaust system has very low back pressure under normal conditions. If the exhaust system is restricted, a significant increase in the exhaust pressure is noticed on the Exhaust Back Pressure Gauge (J 35314-A). Removing the HO2S sensor may set a DTC. When finishing this diagnostic procedure, ensure to clear all codes.
2. 5 - This step will isolate the catalytic converter from the remainder of the exhaust system.
3. 8 - Confirming that the condition has been fixed is essential. If the symptom still exists and the vehicle has a dual exhaust system, proceed to step 2 and repeat diagnostic procedure on the opposite exhaust pipe.
4. 9 - Confirming that the condition has been fixed is essential. If the symptom still exists, proceed to step 2 and repeat the diagnostic procedure.

Diagnostic Procedure - Century & Grand Prix

1. Verify the customers complaint and proceed to next step.
2. Did you review the exhaust symptoms diagnostic information and perform the necessary inspections? If yes, go to next step. If no, go to «EXHAUST SYSTEM CHECK»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l__exhaust-system-check) .
3. Is the system equipped with dual exhaust? If yes, go to «DIAGNOSTIC AIDS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) . If no, go to next step.
4. Remove the pre-catalyst HO2S sensor. Install the Exhaust Back Pressure Gauge (J 35314-A), or equivalent, in place of the HO2S sensor. Start and run the engine. Increase and monitor the engine speed at 2500 RPM. Observe the exhaust system back pressure reading on the gauge. Does the reading exceed 1.25 psi (9 kPa)? If yes, go to next step. If no, go to step 8 .
5. Turn the engine off and place the ignition in the lock position. Remove the exhaust backpressure gauge. Install the pre-catalyst HO2S sensor. Remove the post-catalyst HO2S sensor. Install the exhaust backpressure gauge in place of the post HO2S sensor. Start and run the engine. Increase and monitor the engine speed at 2500 RPM. Observe the exhaust system back pressure reading on the gauge. Does the reading exceed 1.25 psi (9 kPa)? If yes, go to next step. If no, go to step 7 .
6. Check the exhaust system for damage in the exhaust pipe, debris in the exhaust pipe muffler or resonator internal failure or 2-layer exhaust pipe separation. Repair as necessary. After repair, go to step 8 .
7. Replace the catalytic converter. After repair, go to next step.
8. Remove the exhaust backpressure gauge. Install the post-catalyst HO2S sensor. Clear any DTCs using the scan tool. Road test the vehicle to verify the repair. After repair, go to next step.
9. Remove the exhaust backpressure gauge. Install the pre-catalyst HO2S sensor. Clear any DTCs using the scan tool. Road test the vehicle to verify the repair. Did you correct the condition? If yes, system is okay at this time. If no, go to step 2 .

Test Description - Malibu

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

1. 4 - The exhaust system has very low back pressure under normal conditions. If the exhaust system is restricted, a significant increase in the exhaust backpressure is noticed on the exhaust backpressure gauge.
2. 5 - This step will isolate the catalytic converter from the remainder of the exhaust system.
3. 8 - Confirming that the condition has been fixed is essential. If the symptom still exists and the vehicle has a dual exhaust system, proceed to step 2 and repeat diagnostic procedure on the opposite exhaust pipe.

Diagnostic Procedure - Malibu

1. Verify the customers complaint and proceed to next step.
2. Did you review the exhaust symptoms diagnostic information and perform the necessary inspections? If yes, go to next step. If no, go to «EXHAUST SYSTEM CHECK»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l__exhaust-system-check) .
3. Is the system equipped with dual exhaust? If yes, go to «DIAGNOSTIC AIDS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) . If no, go to next step.
4. Remove the AIR check valve or the HO2S that is in front of and closest to the catalytic converter. Install the Exhaust Back Pressure Gauge (J 35314-A), or equivalent, in place of the AIR check valve or HO2S sensor. Start the engine. Observe the exhaust system back pressure reading on the gauge. Does the reading exceed 2 psi (14 kPa)? If yes, go to next step. If no, go to step 8 .
5. Turn ignition switch to LOCK position. Re-install the AIR check valve/HO2S sensor. Remove the post-catalytst HO2S sensor. Install the exhaust backpressure gauge in place of the post HO2S sensor. Start the engine. Increase and monitor the engine speed at 2000 RPM. Observe the exhaust system backpressure reading on the gauge. Does the reading exceed 2 psi (14 kPa)? If yes, go to next step. If no, go to step 7 .
6. Check the exhaust system for damage in the exhaust pipe, debris in the exhaust pipe muffler or resonator internal failure or 2-layer exhaust pipe separation. Repair as necessary. After repair, go to step 8 .
7. Replace the catalytic converter. After repair, go to next step.
8. Remove the exhaust backpressure gauge and reinstall the AIR check valve or the HO2S sensor. Clear any DTCs using the scan tool. Road test the vehicle to verify the repair. Did you correct the condition? If yes, system is okay at this time. If no, go to step 2 .

For dual exhaust systems, a quick check of exhaust flow will help determine which side of the exhaust system is restricted. The side that has less exhaust flow is the side that will be suspect, and diagnosis should begin there.

EXHAUST LEAKAGE

Definition

An exhaust leak may show stains at the area of the leak. The leak may be felt by holding a hand close to the suspected areas or using a smoke pencil. The leak may make a popping or hissing noise. For possible cause and diagnosis, see EXHAUST LEAKAGE DIAGNOSIS table.

EXHAUST LEAKAGE DIAGNOSIS

An audible or physical noise may occur due to a faulty component or damaged components causing a loose or misaligned exhaust system resulting in a rattle or vibration noise. For possible cause and diagnosis, see EXHAUST NOISE DIAGNOSIS table.

EXHAUST NOISE DIAGNOSIS

FUEL EVAPORATIVE SYSTEM

Note. Ensure all vacuum line and EVAP system components are not damaged or missing before proceeding with this test.

EVAP Control System Diagnosis

Manufacturer does not provide testing procedures for many individual systems and components. For EVAP control system diagnosis, see INSPECTION/MAINTENANCE - EVAPORATIVE EMISSION SYSTEM SET PROCEDURE in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article.

Inspection Procedure

Note. Proceed with the following procedure ONLY if referenced by a EVAP diagnostic or repair procedure.

1. Turn ignition switch to OFF position.
2. Remove the EVAP canister purge valve.
3. Lightly tap the EVAP canister purge valve on a hard surface.
4. Check for carbon particles exiting either of the vacuum ports. If no carbon particles were detected, but a blockage was detected during a diagnostic procedure, install the original EVAP canister purge valve and continue with the cleaning procedure. If carbon particles are found during the inspection procedure, replace the EVAP canister purge valve and continue with the cleaning procedure. If a diagnostic procedure directed you to replace the EVAP canister purge valve and no carbon particles were detected, replace the EVAP canister purge valve and return to diagnostic procedure.

1. Raise and support the vehicle.
2. Remove the EVAP canister.
3. Turn OFF the main valve on the EVAP Pressure/Purge Diagnostic Station.
4. Disconnect the hose from the diagnostic station pressure regulator.
5. Using a section of vacuum hose, connect one end onto the diagnostic station pressure regulator.
6. Connect the other end of the vacuum hose to the canister side of the purge pipe.
7. Turn ON the main nitrogen cylinder valve and continue to discharge nitrogen for 15 seconds.
8. If the nitrogen does not dislodge the carbon particles, replace the purge pipe.
9. Return the EVAP pressure/purge diagnostic station to the original condition of the station.
10. Install a new EVAP canister.
11. Lower the vehicle.
12. Install a new EVAP canister purge valve.
13. Return to the diagnostic procedure that sent you here.

The fuel tank leak test is used to locate any fuel or fuel vapor escaping the fuel tank area. Fuel vapors escaping above the fuel level will be detected when the Evaporative (EVAP) emission diagnostics complete one test cycle. The Malfunction Indicator Lamp (MIL) will illuminate after the EVAP diagnostics complete 2 test cycles.

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

1. 3 - This test is to locate fuel leakage in the fuel lines.
2. 4 - This tests for fuel leaks below the fuel tank fuel level.
3. 5 - This test is to locate fuel vapors escaping above the fuel level in the fuel tank.

1. Perform Diagnostic System Check - Engine Controls. See «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.
2. Raise and support the vehicle. Check the fuel tank and fuel pipes for damage or external leaks. Did you find fuel leaking from the fuel tank? If yes, go to step 7 . If no, go to next step.
3. Turn ignition switch to RUN position, engine OFF. Using a scan tool, command the fuel pump ON. Check for fuel leaking from the fuel pipes. Did fuel leak from the fuel pipes? If yes, go to step 8 . If no, go to next step.
4. Install the Fuel Tank Cap Adapter (J 41415-40). Connect the EVAP Pressure/Purge Diagnostic Station (J 41413) to the fuel tank cap adapter. Using a scan tool, seal the EVAP system. DO NOT exceed 15 in. H2O. Using the EVAP pressure/purge diagnostic station, pressurize the fuel tank. Did fuel leak from the fuel tank? If yes, go to step 7 . If no, go to next step.
5. Using the EVAP pressure/purge diagnostic station, maintain pressure in the fuel tank. The fuel tank may need to be partially lowered. Using the Ultrasonic Leak Detector (J 41416), test for leaks above the fuel level in the following locations. The fuel tank, fill limiter vent valve, pressure relief valve and rollover valves. The fuel sender housing and fuel sender seal. The Fuel Tank Pressure (FTP) sensor seal. The EVAP vapor pipes. The fuel fill pipe and hose. Did you locate a fuel leak? If yes, go to next step. If no, see «DIAGNOSTIC AIDS»(/buick/century/vi-1997-2005/remont/testing-diagnostics/#engine-controls-system-testing-engine-component-tests-31l) .
6. Repair the system as necessary.
7. Replace the fuel tank.
8. Replace the leaking fuel pipe.

1. Operate the vehicle under the condition of the customers concern. Under high temperature conditions fuel vapors may increase to the point of EVAP canister vapor saturation. Fuel vapors would then be released into the atmosphere. Once the engine is running and EVAP purge is enabled, all fuel vapor release would be eliminated.
2. Test for fuel leaking in the fuel tank and the fuel feed and return pipes.
3. Test for fuel vapor leaks in the fuel tank, fill limiter vent valve and rollover valves, the fuel fill pipe, hose and fuel fill cap, the fuel sender housing and seal, the Fuel Tank Pressure (FTP) sensor seal and the EVAP vapor pipe.
4. Movement of the EVAP pipes or fuel pipes may help find an intermittent condition.

Required Service

The PCV system may require service for obstructions if any of the following conditions exist

1. Rough idle.
2. Stalling or slow idle speed.
3. Oil leaks.
4. Oil in air cleaner.
5. Sludge in engine.

A leaking PCV valve or hose could cause

1. Rough idle.
2. Stalling.
3. High idle speed.

If engine idles rough, check for clogged PCV valve, or plugged or broken hoses BEFORE adjusting idle. Check PCV valve application to ensure correct valve is fitted. Replace PCV valve if required.

Checking PCV Valve Function

1. Disconnect PCV valve vacuum hose from cylinder head cover. Run engine at idle. Place thumb over open end of PCV valve vacuum hose to check for vacuum. If vacuum does not exist, check for obstruction in source vacuum supply. If source vacuum supply is okay, replace PCV valve.
2. Turn ignition switch to OFF position. Remove PCV valve. Shake valve and listen for rattle of check valve inside PCV valve. If a clear rattle is not heard, replace PCV valve.
3. Visually inspect valve for varnish or deposits which may make PCV valve operation sticky or restricted, or cause incomplete seating of valve. Replace as necessary.
4. Engine must be sealed for PCV system to function as designed. If leakage, sludging or dilution of oil is noted and PCV system is functioning properly, check engine for cause and repair as required to ensure PCV system will continue to function properly.
5. An engine operating without any crankcase ventilation can be damaged, so it is important to replace PCV valve and air cleaner breather (if equipped) at regular intervals (at least every 30,000 miles). Check all hoses and clamps for failure or deterioration.

MISCELLANEOUS CONTROLS

Note. Although some of the controlled devices listed here are not technically engine performance components, they can affect driveability if they malfunction.

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

A/C COMPRESSOR CLUTCH CONTROLS

Note. For A/C compressor clutch circuit testing, see appropriate MANUAL or AUTOMATIC A/C-HEATER SYSTEMS article in AIR CONDITIONING & HEATING.

ELECTRIC COOLING FAN

Note. For electric cooling fan circuit testing, see appropriate ELECTRIC COOLING FANS article in ENGINE COOLING.

TRANSAXLE

Note. For transaxle electronic controls testing, see appropriate DIAGNOSIS article in AUTOMATIC TRANSMISSIONS.

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.

See also:
• DIAGNOSTIC STARTING POINT - ENGINE CONTROLS
• BASIC DIAGNOSTIC PROCEDURES - 3.1L CENTURY, GRAND PRIX & MALIBU
• TROUBLE SHOOTING - NO CODES - 3.1L CENTURY, GRAND PRIX & MALIBU
• COMPONENT LOCATIONS
• DIAGNOSTIC TROUBLE CODE DEFINITIONS
• FUEL SYSTEM DIAGNOSIS
• NO-START DIAGNOSIS
• FUEL PUMP ELECTRICAL CIRCUIT DIAGNOSIS
• SYMPTOMS
• DTC P0201-P0206: INJECTOR CONTROL CIRCUIT
• INTERMITTENTS
• COMPONENT LOCATIONS
• WIRING DIAGRAMS
• IDLE CONTROL SYSTEMS
• ELECTRONIC IGNITION SYSTEM DIAGNOSIS
• FUEL SYSTEM CLEANING
• PARTICULATE CONTAMINANTS IN FUEL TESTING PROCEDURE
• FUEL INJECTOR CLEANING
• DIAGNOSTIC AIDS
• CAMSHAFT POSITION SENSOR
• CRANKSHAFT POSITION SENSOR
• IGNITION RELAY DIAGNOSIS
• RESTRICTED EXHAUST
• EXHAUST LEAKAGE
• TEST DESCRIPTION - MALIBU
• EXHAUST SYSTEM CHECK