Engine Controls - System/component Tests Buick LeSabre VII

INTRODUCTION

Before testing separate components or systems, perform all procedures listed in BASIC TESTING article in this section. Since many computer-controlled and monitored components will set a diagnostic trouble code if they malfunction, it is also recommended that self-diagnosis be performed. See appropriate TESTS W/CODES article in this section.

Note. Testing individual components does not isolate shorts or opens. Perform all voltage tests with a Digital Volt-Ohmmeter (DVOM) with a minimum 10-megohm input impedance, unless stated otherwise in test procedure. Use ohmmeter to isolate wiring harness shorts or opens. The following table provides the location of commonly used diagnostic information. These former "A" and "C" charts are now written in text and inserted into the appropriate location in the new Engine Performance workflow. To familiarize yourself with the Engine Performance workflow, see AA - HOW TO USE THE ENGINE PERFORMANCE SECTION article in this section.

GENERAL MOTORS A & C CHART REFERENCE

Scheme 85

1. Install Tech 1 scan tester. Disconnect boost control solenoid harness connector. Turn ignition on, with engine off. Connect test light between boost control solenoid harness connector terminal "A" and ground. (Scheme 85) Refer to appropriate wiring diagram in «WIRING DIAGRAMS»(/buick/lesabre/vii-1992-1999/remont/testing-diagnostics/#engine-controls-systemcomponent-tests) section. Test light should illuminate. If test light illuminates, go to step 3). If test light does not illuminate, go to next step.
2. Check 15-amp engine control fuse. If fuse is blown, check for a shorted circuit between fuse and boost control solenoid. If fuse is okay, check for an open circuit between fuse and boost control solenoid. (Scheme 85) Repair as necessary.
3. Connect test light between boost control solenoid harness connector terminals "A" and "B". (Scheme 85) Test light should not illuminate. If test light did not illuminate, go to next step. If test light illuminated, go to step 5).
4. Turn ignition off. Disconnect PCM Blue connector. Turn ignition on. If test light illuminated, check for shorted circuit between PCM terminal BE10 and boost control solenoid terminal "B". (Scheme 85) If test light did not illuminate, replace PCM.
5. Using Tech 1 scan tester, select boost control output test under miscellaneous tests. Turn on boost control solenoid using Tech 1 scan tester. Test light should illuminate when boost control solenoid is turned on. If test light did not illuminate, go to next step. If test light illuminated, go to step 7).
6. Connect a test light to battery positive. Using test light, backprobe PCM terminal BE10. Turn on boost control solenoid using Tech 1 scan tester. If test light illuminated, check for open in circuit between PCM terminal BE10 and boost control solenoid terminal "B". (Scheme 85) If test light did not illuminate, check for poor connection at PCM or for a faulty PCM.
7. Reconnect boost control solenoid harness connector. Disconnect boost signal hose between boost control solenoid and by-pass valve actuator. Connect vacuum gauge and read boost signal from solenoid. With transmission in Park, start and idle engine. If vacuum is not present, check circuit for poor connections to solenoid or for faulty solenoid. If vacuum was present, go to next step.
8. Using Tech 1 scan tester, turn off boost control solenoid. Observe vacuum gauge. Vacuum reading should be approximately 15 in. Hg. If vacuum reading is as specified, go to next step. If vacuum reading is not as specified, check for restriction in boost source to boost control solenoid. If restriction is not found, replace boost control solenoid.
9. Check for restriction in boost signal hose between boost control solenoid and by-pass valve actuator. Repair as necessary. If restriction is not found, boost control solenoid is functioning normally.

Ground Circuits

1. Using an ohmmeter, check for continuity to ground on control unit ground terminals. Use appropriate wiring diagram in «WIRING DIAGRAMS»(/buick/lesabre/vii-1992-1999/remont/testing-diagnostics/#engine-controls-systemcomponent-tests) section to determine PCM ground terminals. Resistance to ground should be zero ohms. If reading is other than zero ohms, repair open to circuit ground.
2. Using a DVOM, touch negative lead of voltmeter to a good ground. Touch positive lead of voltmeter to each ground terminal. With vehicle running, voltmeter should indicate less than one volt. If voltmeter reading is one volt or more, check for open, corroded or loose connection on ground lead.

Power Circuits

1. Using a voltmeter, check for battery voltage between control unit constant battery power terminals and ground. If battery voltage is not present, check control unit power supply fuse. If fuse is okay, check for open in power supply or control unit wiring.
2. Turn ignition switch to the ON position. Using a voltmeter, check for battery voltage between control unit ignition power terminals and ground. If battery voltage is not present, check power supply fuse(s). If fuse is okay, check for an open in wiring between fuse and control unit, or check for a defective ignition switch.
3. Connect voltmeter between ground and control unit start (crank) signal terminal. Turn ignition switch to the START position. Battery voltage should be present between control unit start terminal and ground ONLY when ignition switch is in the START position.
4. If voltage is not present, check fuse(s). If fuse is okay, check for an open in wiring between fuse and control unit, or check for a defective ignition switch.

ENGINE SENSORS & SWITCHES

Note. For additional sensor testing specifications, see SENSOR RANGE CHARTS article in this section.

A/C ON (A/C REQUEST) SWITCH TEST

1. Start engine and allow to idle. If a scan tester is available, scan A/C request parameter. Move A/C mode selector back and forth between ON and OFF positions. Scan status should change.
2. If scan tester is not available or scan status does not change, measure voltage between ground and PCM A/C request terminal. For wiring schematics, see mini-schematics under A/C CLUTCH (C-10) & ELECTRIC COOLING FAN (C-12) under «MISCELLANEOUS CONTROLS»(/buick/lesabre/vii-1992-1999/remont/testing-diagnostics/#engine-controls-systemcomponent-tests__miscellaneous-controls) .
3. With A/C mode selector in the ON position, battery voltage should be present. If battery voltage is not present, check for open between A/C mode select switch and PCM A/C request terminal, low A/C refrigerant level causing low pressure switch to open, bad A/C fuse or bad A/C mode select switch.

A/C PRESSURE SENSOR

A malfunction in A/C pressure sensor circuit will set a related diagnostic trouble code. For testing procedures, see TESTS W/CODES article in this section. For wiring schematics, see mini-schematics under A/C CLUTCH (C-10) & ELECTRIC COOLING FAN (C-12) under MISCELLANEOUS CONTROLS .

A/C PRESSURE SWITCH

1. Connect A/C pressure gauges to system and start engine. Note high and low pressure readings. If pressures are normal, go to next step. If pressures are less than normal, check system for leaks. Evacuate and recharge as necessary. If pressures are high, check for system overcharge, overheating or mechanical failure in refrigerant delivery system.
2. Disconnect high and low pressure switches. Install jumper across each switch harness connector to allow A/C system to function normally. Using an ohmmeter, check continuity between pressure switch terminals.
3. Continuity should be present on both high and low switches (if equipped). If continuity is not present, replace A/C pressure switch. For wiring schematics, see mini-schematics under A/C CLUTCH (C-10) & ELECTRIC COOLING FAN (C-12) under «MISCELLANEOUS CONTROLS»(/buick/lesabre/vii-1992-1999/remont/testing-diagnostics/#engine-controls-systemcomponent-tests__miscellaneous-controls) .

BRAKE SWITCH

Disconnect brake switch harness connector. Using an ohmmeter, check continuity between brake switch terminals. Continuity should be present. Depress brake pedal to activate brake switch. Continuity should not be present.

CAMSHAFT POSITION SENSOR

A malfunction in the camshaft position sensor circuit will set a related diagnostic trouble code. For testing procedures, see TESTS W/CODES article in this section.

CRANKSHAFT POSITION SENSOR

A malfunction in the crankshaft position sensor circuit will set a related diagnostic trouble code. For testing procedures, see TESTS W/CODES article in this section. To diagnose position crankshaft sensor, the following procedures can be used

1. If a scan tester is available, scan RPM parameter while cranking engine. If RPM is indicated, crankshaft position sensor is operating properly.
2. If scan tester is not available, disconnect crankshaft position sensor harness connector. Set ohmmeter to 2-k/ohm position, and measure resistance across sensor terminals. Resistance should be 800-1200 ohms.
3. Set voltmeter on the 2-volt AC scale. Crank engine and measure output voltage across sensor terminals. Voltmeter reading should be .8-1.4 volts. If resistance reading is not as specified or sensor does not produce the specified output voltage reading, repair faulty wiring or faulty crankshaft position sensor.

ENGINE COOLANT TEMPERATURE (ECT) SENSOR

If a coolant sensor-related diagnostic trouble code is present, see TESTS W/CODES article in this section. An out-of-calibration sensor may not set a diagnostic trouble code. Use following procedure to test sensor calibration. Disconnect ECT sensor connector. Measure resistance between sensor terminals. Resistance should be high when engine is cold and drop as engine warms. See ECT SENSOR RESISTANCE VALUES .

ECT SENSOR RESISTANCE VALUES (1)

INTAKE AIR TEMPERATURE (IAT) SENSOR

IAT sensor may also be referred to as a Manifold Air Temperature (MAT) sensor. If a IAT sensor related code is present, see TESTS W/CODES article in this section. An out-of-calibration sensor may not set a diagnostic trouble code. Use following procedure to test calibration. Disconnect IAT sensor harness connector. Connect ohmmeter between sensor terminals. Sensor resistance should be as specified. See IAT SENSOR RESISTANCE VALUES . After vehicle has sat overnight, MAT sensor and coolant sensor should have close to the same resistance reading.

IAT SENSOR RESISTANCE VALUES (1)

KNOCK SENSOR (KS)

Disconnect knock sensor harness connector. Using an ohmmeter, measure knock sensor resistance between sensor terminal and engine block. Resistance should be 3300-4500 ohms. Connect DVOM between sensor terminal and ground. Set voltmeter to 2-volt AC scale. Start and idle engine. Tap on engine block near sensor. A signal should be indicated on voltmeter. If no signal is indicated, replace knock sensor. Also, see TIMING CONTROL SYSTEMS under IGNITION SYSTEM. If a code is present, see TESTS W/CODES article in this section.

MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR (C-1)

1. A malfunction in the MAP sensor circuit should set a related diagnostic trouble code in PCM memory. If a code is present, see «TESTS W/CODES»(/buick/lesabre/vii-1992-1999/remont/testing-diagnostics/#engine-controls-tests-wcodes) article in this section. An out-of-calibration sensor may not set a diagnostic trouble code. Use following procedure to test sensor calibration. If driveability problems exist, MAP sensor failure is suspected and no MAP code is present, disconnect MAP sensor connector. (Scheme 86) If driveability condition improves, replace MAP sensor.
2. With ignition on and engine off, check MAP sensor parameter using a scan tester connected to Data Link Connector (DLC). Voltage should be as specified. See «MAP SENSOR VOLTAGE RANGE»(/buick/lesabre/vii-1992-1999/remont/testing-diagnostics/#engine-controls-systemcomponent-tests). If MAP sensor voltage is as specified, go to step 3). If voltage is not as specified, check for 5-volt reference supplied to sensor. Check harness integrity. If no problems are evident, replace MAP sensor.
3. Using a hand-held vacuum pump, apply 10 in. Hg to MAP sensor, and note voltage change. Voltage should drop about 1.2-2.3 volts less than as specified in table. If voltage is not as specified or voltage reading does not immediately follow vacuum change, MAP sensor is faulty.

Scheme 86

MAP SENSOR VOLTAGE RANGE

MASS AIRFLOW (MAF) SENSOR

A malfunction in the MAF sensor circuit will set a related diagnostic trouble code. For testing procedures, see Code P0101 in the TESTS W/CODES article in this section. If driveability problems exist, MAF sensor failure is suspected and no Code P0101 is present, disconnect MAF sensor connector. If driveability improves, replace MAF sensor.

MANIFOLD AIR TEMPERATURE (MAT) SENSOR

MAT sensor may also be referred to as an Intake Air Temperature (IAT) sensor. See INTAKE AIR TEMPERATURE (IAT) SENSOR . A malfunction in the MAT sensor will set a related diagnostic trouble code. For testing procedures, see TESTS W/CODES article in this section.

OXYGEN SENSOR (O2S)

1. Start engine and warm to operating temperature. Disconnect oxygen sensor. Connect a DVOM between lead of oxygen sensor and ground. Place DVOM on the 2-volt scale. Voltmeter reading should increase to greater than .8 volt.
2. Using another DVOM on the 20-volt scale, connect voltmeter in series between the oxygen sensor wire from PCM and positive post of battery. Reading on voltmeter connected to oxygen sensor should decrease to a low voltage (less than .3 volt).
3. If a second DVOM is not available, install short jumper in oxygen sensor wire from PCM. Hold jumper in one hand and touch positive post of battery with other hand. This should cause oxygen sensor to produce less than .3 volt. For additional testing procedures, see «TESTS W/CODES»(/buick/lesabre/vii-1992-1999/remont/testing-diagnostics/#engine-controls-tests-wcodes) article in this section.

PARK/NEUTRAL POSITION (PNP) SWITCH (C-1)

1. Disconnect PNP switch harness connector. Connect ohmmeter between the PNP switch terminals. (Scheme 87) Continuity should be present only when gear shift selector is in Park or Neutral. If continuity is present, go to next step. If continuity is not present, check PNP switch adjustment or replace defective PNP switch.
2. With PNP switch connector disconnected, turn ignition on. Check for 12 volts on the Orange/Black wire of PNP switch harness. If 12 volts are not present, check for open or short to ground between switch harness connector and PCM.

Scheme 87

POWER STEERING PRESSURE (PSP) SWITCH

1. If scan tester is available, scan power steering pressure switch status. Note status with engine running and wheels in straight-ahead position. Turn steering wheel to full left or right position and again note status. If status changed, power steering pressure switch is okay. If status did not change or scan tester is not available, go to next step.
2. Turn ignition off. Disconnect PSP switch harness connector. Connect ohmmeter between PSP switch terminals. Start engine. With no-load on power steering, continuity should not be present. Turn steering wheel to full left or right position. Continuity should now be present. If readings are not as specified, replace PSP switch.
3. With PSP switch connector disconnected and ignition on, check for 1battery voltage on PSP switch harness from PCM. If battery voltage is not present, check for open or short to ground in harness between PSP switch connector and PCM.

THROTTLE POSITION (TP) SENSOR

Install jumper wires to enable connection of a DVOM in parallel between TP sensor harness connectors. Connect DVOM positive lead to Dark Blue TP sensor signal wire terminal. Connect negative lead to Black, Black/Orange or Purple sensor ground wire terminal. (Scheme 88) Turn ignition on, with engine off. Signal voltage should gradually change from less than one volt at closed throttle to about 5.0 volts at wide open throttle position. If reading is not as specified, adjust or replace TP sensor. See ADJUSTMENTS article in this section.

A malfunction in the TP sensor circuit should set a related diagnostic trouble code. For further information, see TESTS W/CODES article in this section.

Scheme 88

VEHICLE SPEED SENSOR (PM GENERATOR TYPE)

Disconnect vehicle speed sensor harness connector (located in transaxle). Place gear selector in Neutral. Raise vehicle drive wheels off the ground. Turn drive wheels by hand (greater than 3 MPH). Measure AC signal voltage between sensor terminals. Voltage reading should vary from 0.1-0.5 volt AC as the wheel is turned. If reading is not as specified, replace vehicle speed sensor.

VEHICLE SPEED SENSOR (LED TYPE)

A speed sensor or buffer malfunction should set a related diagnostic trouble code in PCM memory. If a code is set, refer to the TESTS W/CODES article for diagnosis in this section.

Idle Air Control (IAC) Motor & Idle Speed Control (ISC) Motor

See IDLE CONTROL SYSTEM .

A/C Clutch Relay

See MISCELLANEOUS CONTROLS .

Electric AIR Pump Relay

See EMISSION SYSTEMS & SUB-SYSTEMS .

Fuel Pump Relay

See FUEL SYSTEM .

SOLENOIDS

Note. All PCM-controlled solenoids should have at least 20 ohms of resistance when checked with positive ohmmeter lead connected to power supply terminal of solenoid and negative ohmmeter lead connected to ground terminal of solenoid. Some solenoids are equipped with internal diodes. On these solenoids, resistance values will differ if ohmmeter test leads are reversed.

AIR By-Pass Valve Solenoid

See EMISSION SYSTEMS & SUB-SYSTEMS .

Canister Purge Solenoid

See EMISSION SYSTEMS & SUB-SYSTEMS .

Cruise Control Vent Solenoid (4.0L)

A malfunction in the cruise control vent solenoid circuit will set a related diagnostic trouble code. For further information, see TESTS W/CODES article in this section.

EGR Control Solenoid

See EMISSION SYSTEMS & SUB-SYSTEMS .

FUEL DELIVERY

Note. For fuel system pressure testing, see BASIC TESTING article in this section.

Fuel Pressure Regulator

1. Install fuel pressure gauge to fuel rail fuel pressure test fitting. Remove vacuum hose from fuel pressure regulator. Turn ignition on and note fuel pressure on gauge.
2. Start engine. Check for manifold vacuum at pressure regulator vacuum hose. If vacuum is not present, repair as necessary. Reconnect vacuum hose to pressure regulator and note fuel pressure on gauge. Compare first and second reading.
3. Fuel pressure reading should be 4-7 psi (.28-.49 kg/cm 2 ) less with vacuum hose installed. Fuel pressure should decrease as vacuum increases. If results are not as specified, replace fuel pressure regulator.

Note. For further fuel pump circuit diagnosis, refer to appropriate FUEL SYSTEM test under NO-START DIAGNOSIS (A-3) in BASIC TESTING article in this section.

Fuel Pump Relay (A-5)

1. Disconnect fuel pump relay connector. See «COMPONENT LOCATIONS»(/buick/lesabre/vii-1992-1999/remont/testing-diagnostics/#engine-controls-systemcomponent-tests) at end of article to locate fuel pump relay. Apply battery voltage and ground to fuel pump relay winding terminals. To identify fuel pump relay terminals, see appropriate wiring diagram in «WIRING DIAGRAMS»(/buick/lesabre/vii-1992-1999/remont/testing-diagnostics/#engine-controls-systemcomponent-tests) section.
2. Using an ohmmeter, check for continuity between fuel pump relay power supply terminal and fuel pump drive terminal. Continuity should exist ONLY with relay energized. If relay does not test as indicated, replace relay.
3. To by-pass fuel pump relay (to test fuel pump and wiring when fuel pump is not energizing), see FUEL PUMP RELAY BY-PASS PROCEDURE below.

Fuel Pump Relay By-Pass Procedure

1. If fuel pump will not energize, relay may be by-passed to test fuel pump and related wiring. (Scheme 89) Turn ignition off. Disconnect fuel pump relay connector.
2. Using a fused jumper wire, apply battery voltage to fuel pump test connector (located in engine compartment). For fuel pump test connector location, see «COMPONENT LOCATIONS»(/buick/lesabre/vii-1992-1999/remont/testing-diagnostics/#engine-controls-systemcomponent-tests) at end of this article. (Scheme 105)- (Scheme 106).
3. If fuel pump runs and relay tests okay, check for faulty connections at relay. If fuel pump does not run, check for faulty wiring between relay and fuel pump or replace defective fuel pump.

Scheme 89

Oil Pressure Switch Fuel Pump Back-Up

With engine idling, disconnect fuel pump relay. Engine should continue to run through oil pressure switch back-up circuit. If engine stalls, check oil pressure switch and related wiring.

Fuel Injector(s)

Disconnect fuel injector harness connector. Measure resistance across injector terminals at each injector. Resistance should be as specified. See INJECTOR RESISTANCE SPECIFICATIONS .

INJECTOR RESISTANCE SPECIFICATIONS (1)

Note. If injectors are dirty, they should be cleaned using approved injector cleaning procedure before performing INJECTOR BALANCE TEST.

Injector Balance Test (C-2)

The injector balance test is used to pulse the injector for a precise amount of time, spraying a measured amount of fuel in the intake manifold. As each injector is pulsed, a drop in fuel rail pressure occurs. This pressure drop can be recorded and compared to other injectors. An injector with a pressure drop of 1.5 psi (.11 kg/cm 2 ) or more, greater than or less than other injectors, should be considered faulty.

Note. Allow engine to cool down to avoid irregular readings due to "hot soak" fuel boiling. To prevent flooding, the INJECTOR BALANCE TEST should not be repeated more than once without starting and running engine.

1. Ensure engine is at normal operating temperature. Connect Fuel Pressure Gauge (J-34730-1) to pressure test port. Energize fuel pump using fuel pump test connector or Tech 1 scan tester.
2. Bleed air from fuel gauge and hose to ensure accurate gauge reading. Repeat this procedure until all air is bled from system. Run fuel pump and note fuel pressure. Fuel pressure should be as specified. See «FUEL PRESSURE RANGE»(/buick/lesabre/vii-1992-1999/remont/testing-diagnostics/#engine-controls-systemcomponent-tests) . If fuel pressure range is not as specified, see BASIC FUEL SYSTEM CHECKS in «BASIC TESTING»(/buick/lesabre/vii-1992-1999/remont/testing-diagnostics/#engine-controls-basic-testing) article in this section.
3. Turn fuel pump off. When fuel pump stops, pressure may slightly drop then should hold steady. If fuel pressure does not hold steady, refer to BASIC FUEL SYSTEM CHECKS in «BASIC TESTING»(/buick/lesabre/vii-1992-1999/remont/testing-diagnostics/#engine-controls-basic-testing) article in this section.
4. Install Fuel Injector Tester (J-39021) to an injector. Set amperage supply selector switch to "Balance Test, 0.5-2.5 amp." position. Cycle fuel pump on and off to pressurize fuel system. Record stabilized fuel pressure.
5. Depress "Push To Start Test" button on fuel injector tester to energize injector. Note fuel pressure the instant fuel gauge needle stops. Record fuel pressure reading. Perform the same test to all injectors.
6. To obtain pressure drop values, subtract second pressure reading from first pressure reading on each injector. Add all pressure drop values and divide by number of injectors to obtain an average pressure drop.
7. Retest an injector that appears faulty. Replace any injector with a 1.5 psi (.11 kg/cm 2 ) difference, either greater than or less than the average pressure drop. If injectors are all okay, remove test equipment, plug in disconnected harness connectors and review SYMPTOMS in «TESTS W/O CODES»(/buick/lesabre/vii-1992-1999/remont/testing-diagnostics/#engine-controls-tests-wo-codes) article in this section.

FUEL PRESSURE RANGE CHART

Fuel Injector Leak Test

1. Turn engine off. Relieve fuel pressure. Access fuel injectors. Connect Fuel Injector Tester (J-39021) to vehicle battery and to a fuel injector. If coolant temperature is 50-95°F (10-35°C), go to next step. If coolant temperature is not 50-95°F (10-35°C), go to step 5).
2. Set fuel injector tester's amperage supply selector switch to "Coil Test 0.5 amp" position. Connect a Digital Volt-Ohmmeter (DVOM) to fuel injector tester. Set DVOM to tenths scale (0.0).
3. Ensure engine coolant temperature is 50-95°F (10-35°C). Press "Push To Start" tester button. Observe DVOM. Voltage reading may climb during test. Record lowest voltage displayed immediately after activation.
4. Perform voltage reading on all injectors. If voltage reading is erratic or falls out of specified range, perform injector balance test or replace faulty injector. See «INJECTOR TEST VOLTAGE RANGE»(/buick/lesabre/vii-1992-1999/remont/testing-diagnostics/#engine-controls-systemcomponent-tests) or INJECTOR BALANCE TEST (C2).
5. Press "Push To Start" button on fuel injector tester. Observe DVOM. Voltage reading may climb during test. Record lowest voltage displayed immediately after activation. Perform voltage reading at least twice on all injectors.
6. If voltage reading is erratic or is greater than 9.5 volts, replace affected fuel injector. If voltage reading is not erratic or not greater than 9.5 volts, go to next step.
7. From recorded voltages (except readings greater than 9.5 volts), identify highest voltage reading and subtract from the other recorded voltages. If subtracted value is greater than 0.6 volts, replace affected fuel injector. If subtracted value is less than 0.6 volts, perform injector balance test. See INJECTOR BALANCE TEST (C2).

INJECTOR TEST VOLTAGE RANGE

Oxygen Sensor

See ENGINE SENSORS & SWITCHES .

IDLE AIR CONTROL (IAC) MOTOR

1. Disconnect harness connector to motor. Check resistance across IAC coil terminals "A" and "B" (coil "B") and "C" and "D" (coil "A"). (Scheme 90) Resistance should be 40-80 ohms. If resistance is as specified, go to next step. If resistance is not as specified, replace IAC motor.
2. Check resistance between IAC terminals "B" to "C" and "A" to "D". Resistance should be infinite. If resistance is not as specified, replace IAC motor.

Note. Additional testing of Idle Air Control (IAC) motor requires an IAC motor actuator and node light, or a scan tester capable of cycling PCM output devices (General Motors Tech 1).

Scheme 90

IGNITION SYSTEM

Note. For basic ignition system checks, see BASIC TESTING article in this section.

Ignition Control (IC) Timing Advance System

1. A malfunction in the IC circuit (formerly referred to as the EST circuit) should set a related diagnostic trouble code. Start engine and warm to operating temperature. On vehicles equipped with a manual transmission, increase engine speed to about 2000 RPM. On vehicle equipped with an automatic transmission, slightly increase idle speed.
2. Ground DLC "test" terminal "B" (not applicable to all models). A noticeable change in engine speed should occur. If no change occurs, see DIAGNOSTIC CIRCUIT CHECK in «BASIC TESTING»(/buick/lesabre/vii-1992-1999/remont/testing-diagnostics/#engine-controls-basic-testing) article in this section.

Knock Sensor (KS) System Without KS Controller (C-5)

1. An open or short circuit on the KS wire to the PCM will set a related diagnostic trouble code. A false detonation signal will not cause PCM to set a code.
2. If a scan tester is available, connect it to the DLC. Tap on engine next to knock sensor and note "knock" parameter. Knock should be indicated on scan tester.
3. If a scan tester is not available, connect tachometer to engine. Start engine and hold RPM above idle. Using a metal object, tap on engine close to knock sensor. A noticeable decrease in engine RPM should occur. If no RPM decrease occurred, check knock sensor-to-PCM circuit.
4. On vehicles equipped with automatic transmission, it may be necessary to place transmission in Drive for timing change to occur. Also, see KNOCK SENSOR (KS) under «ENGINE SENSORS & SWITCHES»(/buick/lesabre/vii-1992-1999/remont/testing-diagnostics/#engine-controls-systemcomponent-tests__engine-sensors-switches) .

Knock Sensor (KS) System With KS Controller (C-5)

1. An open or short circuit on KS wire to PCM will cause a loss of 12-volt KS controller signal. This will cause PCM to fully retard ignition timing.
2. If scan tester is available, connect it to the DLC. Tap on engine next to knock sensor and note "knock" parameter. Knock should be indicated on scan tester.
3. If scan tester is not available, connect a DVOM to PCM ESC signal terminal. With engine idling, 12 volts should be present at this terminal. Using a metal object, tap on engine close to knock sensor. Voltage signal at PCM terminal should drop to zero volts, and return when knock signal ceases.
4. If signal does not respond as described, check knock sensor signal to KS controller. On vehicles equipped with automatic transmission, it may be necessary to place transmission in Drive for timing change to occur. Also, see KNOCK SENSOR (KS) under «ENGINE SENSORS & SWITCHES»(/buick/lesabre/vii-1992-1999/remont/testing-diagnostics/#engine-controls-systemcomponent-tests__engine-sensors-switches) .

AIR Pump (Belt-Driven)

Accelerate engine to approximately 1500 RPM and observe airflow from hoses. If airflow increases as engine is accelerated, pump is working properly. If airflow does not increase, check hoses, pump belt tension, leaky valves or defective air injection pump.

Check Valve

Detach check valve and blow through valve in direction of check valve flow (to cylinder head). Attempt to suck air back. Replace valve if airflow is allowed against the direction of flow.

EXHAUST GAS RECIRCULATION (C-7)

There are 3 types of EGR systems used: pulse width modulated backpressure (positive and negative) EGR with a control solenoid, pulse width modulated backpressure (positive and negative) EGR without a control solenoid, digital and linear EGR. See EGR SYSTEM IDENTIFICATION .

EGR SYSTEM IDENTIFICATION

System Test (Vacuum Operated)

Start and run engine to normal operating temperature. With engine at idle, push up on underside of EGR diaphragm. RPM should drop as EGR valve is opened. If RPM does not drop, remove EGR valve and check for blocked EGR passages. If RPM drops as diaphragm is lifted and EGR vacuum supply is regulated by an PCM-controlled solenoid, verify vacuum is available to solenoid at 2000 RPM and check solenoid using appropriate procedure. See appropriate EGR CONTROL SOLENOID procedure.

EGR Control Solenoid (Normally Closed)

1. Disconnect EGR solenoid electrical harness connector and vacuum hoses. Connect a hand-held vacuum pump to solenoid vacuum source port. Connect vacuum gauge to solenoid EGR port. Pump up vacuum pump. Vacuum should not be present at port to EGR valve.
2. Activate EGR solenoid with a 12-volt power supply. Vacuum should now be present or registered at vacuum gauge. If vacuum is not present, check EGR solenoid resistance. Solenoid should have at least 20 ohms of resistance.

EGR Control Solenoid (Normally Open)

1. Disconnect solenoid harness connector. Install vacuum pump to vacuum source side of solenoid. Apply vacuum to solenoid. Vacuum should pass through when solenoid connector is disconnected.
2. Apply battery voltage and ground to solenoid terminals. With solenoid energized, apply vacuum to solenoid. Vacuum should not pass through solenoid. If results are not as specified, check EGR solenoid resistance. Solenoid should have at least 20 ohms of resistance.

Linear EGR Valve

A malfunction in the EGR circuit will set a related diagnostic trouble code, see TESTS W/CODES article in this section.

Negative Backpressure EGR Valve

With engine off, disconnect vacuum hose to EGR valve. Connect vacuum pump to EGR and apply 10 in. Hg. EGR diaphragm should move up and stay up for 20 seconds. If valve does not operate as indicated, replace EGR valve.

Positive Backpressure EGR Valve

1. Place transmission in Park or Neutral. Set parking brake and block drive wheels. Connect tachometer. With engine running at normal operating temperature, run engine at 2000 RPM.
2. Disconnect vacuum hose from EGR valve and plug hose. EGR valve diaphragm should move down and engine RPM should increase. NOTE: On some engines with PCM-controlled solenoid, EGR vacuum is locked out in Park/Neutral and solenoid must be by-passed with vacuum supply hose.
3. Reconnect vacuum hose. EGR diaphragm should move up and engine RPM should decrease. A slight vibration of diaphragm plate may be noticed in backpressure EGR valves.
4. If engine RPM did not change and EGR diaphragm moved, the EGR valve is functioning properly. If engine RPM did not change and diaphragm did not move, remove EGR valve and apply 10 in. Hg to EGR vacuum signal port. EGR valve should not open.
5. If EGR valve opens, replace EGR valve. With vacuum still applied, direct a stream of air (15 psi maximum) into valve seat. EGR valve should open completely.
6. If air is not available, connect a short piece of hose over EGR valve seat. Connect vacuum pump to signal port. With thumb plugging intake port of EGR valve, operate vacuum pump while alternately blowing through hose and pausing.
7. With vacuum present at signal port, EGR valve should open while pressure is applied and should close when no vacuum is present.

FUEL EVAPORATION CONTROL (C-3)

Note. One of 2 types of solenoid is used: normally open or normally closed. See CANISTER PURGE SOLENOID IDENTIFICATION .

CANISTER PURGE SOLENOID IDENTIFICATION

Canister Purge Solenoid (Normally Closed)

1. Disconnect canister purge solenoid harness connector and vacuum hose. Apply 10 in. Hg to ported intake manifold vacuum side of solenoid valve. If vacuum holds, go to next step. If vacuum does not hold, replace canister purge solenoid.
2. Using a 12-volt power source, energize canister purge solenoid. Vacuum should release. If vacuum does not release, replace canister purge solenoid. Solenoid resistance should be at least 20 ohms.

Canister Purge Solenoid (Normally Open)

1. Disconnect canister purge solenoid harness connector and vacuum hose. Apply vacuum to ported intake manifold vacuum side of solenoid valve. If vacuum holds, go to next step. If vacuum does not hold, replace canister purge solenoid.
2. Using a 12-volt power source, energize canister purge solenoid. Vacuum should release. If vacuum does not release, replace canister purge solenoid. Solenoid resistance should be at least 20 ohms.

Fuel Tank Pressure Control Valve

Apply approximately 15 in. Hg to fuel tank pressure control valve. The diaphragm should hold vacuum for at least 20 seconds. If fuel tank pressure control valve does not hold vacuum, replace tank pressure control valve.

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

Checking PCV Valve Function

1. Remove PCV valve from rocker cover. Run engine at idle. Place thumb over open end of valve to check for vacuum. If there is no vacuum at valve, check for obstruction in manifold port, hoses or PCV valve. Repair or replace as necessary.
2. Turn engine off. Remove PCV valve. Shake valve and listen for rattle of check valve inside. 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 if necessary.
4. An engine must be sealed for the PCV system to function as designed. If leakage, sludging or dilution of oil is noted and the 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.

HOT LIGHT OR COOLANT TEMPERATURE LIGHT

Note. These checks assume vehicle is not overheating. Verify proper operation of cooling system prior to diagnosing hot light. The coolant temperature sensor, in rare cases, may fail to indicate correct coolant temperature without setting a diagnostic trouble code (Code 14 or 15). This could result in hot light turning on without having an overheating condition. It could also result in engine overheating without hot light turning on. Check coolant sensor temperature-to-resistance values in SENSOR RANGE CHARTS article in this section.

Hot light is powered by the 10-amp INDIC or GAGES fuse. Light will turn on when PCM provides a ground for the circuit. If circuit grounds between light and PCM, light will illuminate any time the ignition is turned on.

1. Turn ignition on with engine off (bulb test position). If hot light illuminates, go to step 3). If hot light does not illuminate, check the following and proceed to next step: 10-amp INDIC or GAGES fuse. Faulty instrument cluster bulb. Open circuit between fuse and hot light.
2. Backprobe PCM hot light driver terminal with a test light to battery voltage. Turn ignition on. If test light does not illuminate, PCM terminal connection is bad or PCM is faulty. If test light illuminates, turn ignition off. Disconnect PCM connectors. Jumper PCM hot light driver harness terminal to ground. Turn ignition on. If hot light does not illuminate, check for open circuit between hot light and PCM. If all circuits are okay and power is available to light, instrument cluster must be replaced.
3. Start engine. If hot light goes off, no problem is evident. If hot light is on, turn ignition off. Disconnect PCM connector. Probe PCM hot light driver harness terminal with a test light to battery voltage. If test light does not illuminate, replace PCM. If test light illuminates, repair short to ground in hot light driver circuit. If circuit is okay, replace instrument cluster.

TRANSMISSION (C-8)

Note. Computerized transmission controls are also covered in greater detail in appropriate TRANSMISSION SERVICING & REPAIR manual.

Converter Clutch Solenoid

Disconnect harness connector to Torque Converter Clutch (TCC) solenoid. Measure resistance between TCC solenoid terminals "A" and "D". (Scheme 91) Solenoid resistance should be greater than 20 ohms.

Note. Some solenoids have an internal pressure switch in series with the solenoid winding and will not show continuity until that pressure switch is applied by transmission hydraulic pressure. (Scheme 91)

Converter Lock-Up Signal At Transmission

1. Warm engine to operating temperature. Raise vehicle and support drive wheels. Support suspension where necessary to prevent damage to drive axles.
2. Disconnect converter clutch connector at transmission. Connect a test light across terminals "A" and "D" of converter clutch harness. Start engine and place transmission in Drive. Accelerate vehicle to 45 MPH and note test light.
3. If test light is not on, check solenoid power supply wire of harness for open or short to ground. Check ground circuit for open between harness connector and PCM. If harness is okay, see CONVERTER LOCK-UP SIGNAL FROM PCM below.

Converter Lock-Up Signal From PCM

1. Warm engine to operating temperature. Raise vehicle and support drive wheels. Support suspension where necessary to prevent damage to drive axles.
2. Connect a test light to battery voltage. Touch TCC control driver terminal with test light. On some vehicles, this is terminal "F" of Data Link Connector (DLC). (Scheme 91) Accelerate vehicle to 45 MPH and note test light. If test light does not illuminate, problem is a faulty PCM connector or PCM.

Scheme 91

A/C CLUTCH (C-10) & ELECTRIC COOLING FAN (C-12)

Note. For additional information on electric cooling fans, see ENGINE COOLING FAN article in ENGINE COOLING section.

1. Disconnect A/C clutch relay harness connector. Using proper mini-schematic and an ohmmeter, check continuity between A/C clutch relay winding terminals. (Scheme 92)- (Scheme 104). Continuity should exist. Check continuity between clutch drive circuit terminals of relay. Continuity should not exist.
2. Using jumper wires, apply ground and battery voltage to relay winding of relay. Continuity should now exist between clutch drive circuit terminals of relay. Replace A/C clutch relay if readings are not as specified.

Cooling Fan System & Quad-Driver Check

1. Connect a test light to battery voltage. Touch test light probe to the cooling fan control driver terminal of the PCM. (Scheme 92)- (Scheme 104). Disconnect coolant temperature sensor. This should set a code, causing PCM to engage cooling fan through relay. On some models, it may be necessary to jumper the coolant temperature sensor harness connectors. On some models, grounding the DLC with the ignition on and engine off will cause the PCM to activate the cooling fan control driver (ground circuit).
2. If test light illuminates and cooling fan does not come on, check cooling fan relay, power circuits, cooling fan motor, and relay and fan motor ground circuits. If test light does not illuminate, problem is a faulty PCM connector or PCM. Clear diagnostic trouble code(s) from PCM memory after testing.
3. If cooling fan functions normally during testing but fails to operate under normal conditions, check PCM monitored inputs which affect cooling fan operation. These include the following: coolant temperature sensor, A/C request signal from A/C control switch and A/C pressure sensor, or pressure/temperature switch signals (if equipped).

Cooling Fan Relay

1. Disconnect cooling fan relay harness connector. Using an ohmmeter, check continuity of relay winding. (Scheme 92)- (Scheme 104). Continuity should exist. Check continuity across power delivery terminals of relay. With relay not energized, no continuity should exist.
2. With ohmmeter still attached to power delivery terminals of relay, apply battery voltage and ground to energize relay winding. Continuity should now be present between cooling fan relay power delivery terminals. Replace cooling fan relay if readings are not as specified.

Cooling Fan Motor

Disconnect cooling fan motor harness connector. Apply battery voltage to one of the fan motor terminals and jumper the other terminal to ground. Fan motor should activate. If fan motor does not activate, replace faulty fan motor.

Note. For a more specific system testing, refer to the following C-10 or C-12 diagnostic charts. If any chart other than a C-10 or C-12 chart is referenced, see TESTS W/CODES article in this section.

Note. In following charts, the terms ECM and PCM can be used interchangeably.

CHART C-12A, COOLING FAN CIRCUIT DIAGNOSIS (1 OF 4)

Right cooling fan (fan No. 1) is a low speed fan. Left cooling fan (fan No. 2) is a low and high speed fan. Power for fan motor goes through a 40-amp fusible link to terminal No. 87 of fan relays. Fan relays are energized when a ground circuit is completed through Powertrain Control Module (PCM) quad-driver No. 4. PCM energizes right cooling fan (fan No. 1) relay through PCM terminal WD11 when Engine Coolant Temperature (ECT) sensor indicates 212°F (100°C) or when A/C is requested. PCM energizes left cooling fan (fan No. 2) relay if A/C refrigerant pressure reaches 210 psi (14.8 kg/cm 2 ) or ECT sensor indicates 226°F (108°C).

Note. Test numbers refer to numbers on diagnostic charts.

1. Selecting Tech 1 miscellaneous tests, FAN 1, causes PCM to ground circuit No. 335. Right cooling fan (fan No. 1) should run.
2. Selecting Tech 1 miscellaneous tests, FAN 2, allows control of circuit No. 473. Left cooling fan (fan No. 2) should run.
3. When jumpering A/C head pressure switch harness connector, PCM should operate left cooling fan (fan No. 2) on high speed.

Diagnostic Aids

An intermittent may be caused by a poor connection, rubbed-through wire insulation or a wire broken inside the wire insulation. Check PCM harness connector for backed-out terminals. Connect a DVOM between affected terminal and ground. Wiggle related wires and connectors while watching DVOM for a voltage reading change. Ensure ECT sensor is not mis-scaled. See Diagnostic Trouble Code (DTC) P0118 chart in TESTS W/CODES article in this section. Ensure engine cooling system functions properly.

Scheme 92

Scheme 93

CHART C-12B, COOLING FAN ON AT ALL TIMES (2 OF 4)

Note. Test numbers refer to numbers on diagnostic charts.

1. Checks if circuit No. 335 is shorted to ground, which would keep relay closed at all times.
2. Checks if circuit No. 473 is shorted to ground. If test light comes on, wire is shorted to ground. Continuing with chart diagnosis will isolate short.
3. If test light is off after disconnecting PCM, ensure circuit No. 335 is not shorted to battery voltage. If circuit is not shorted to battery voltage, PCM is shorted internally.
4. If test light is off after disconnecting PCM, ensure circuit No. 473 is not shorted to battery voltage. If circuit is not shorted to battery voltage, PCM is shorted internally.

Scheme 94

CHART C-12C, COOLING FAN NO LOW SPEED FAN (3 OF 4)

Note. Test numbers refer to numbers on diagnostic charts.

1. Checks for battery voltage at relay harness connector terminals No. 30 and 85.
2. Jumpering relay terminals No. 30 and 87 by-passes relay, which should cause fans to run if fan motors and wiring are okay.
3. Select Tech 1 miscellaneous tests, FAN 1. Turn fans on. PCM should ground circuit No. 335. At this point, test light should be on if PCM is good and circuit No. 335 is not open.
4. Checks for battery voltage and ground to fan motor. Test light on at this point indicates a faulty fan motor connection or motor.

Scheme 95

CHART C-12D, COOLING FAN NO HIGH SPEED FAN (4 OF 4)

Note. Test numbers refer to numbers on diagnostic charts.

1. Battery voltage should be present at left fan relay (fan No. 2) terminals No. 30 and 85 with ignition on.
2. Jumpering relay terminals No. 30 and 87 by-passes left fan relay (fan No. 2). If fan runs, fan relay is faulty.
3. Checks circuit No. 473 back to PCM. If circuit No. 473 is okay, left fan relay (fan No. 2) is faulty.

Scheme 96

CHART C-10A, A/C COMPRESSOR CLUTCH CIRCUIT DIAGNOSIS (1 OF 3) MANUAL A/C-HEATER

Powertrain Control Module (PCM) delays A/C compressor clutch engagement momentarily after A/C is turned on. This delay allows Idle Air Control (IAC) motor to adjust engine RPM before A/C compressor clutch engages. PCM also disengages A/C compressor clutch during Wide Open Throttle (WOT). A/C compressor clutch is energized when PCM grounds circuit No. 459. PCM may engage A/C compressor clutch during engine cranking.

Note. Test numbers refer to numbers on diagnostic chart.

1. A/C compressor clutch should not be engaged with engine running if an A/C mode is not selected at control head.
2. A/C compressor clutch should apply if conditions under NOTICE at top of chart are met.
3. Checks for an A/C request signal from control head to pressure cycling switch.

Scheme 97

Scheme 98

CHART C-10A, A/C COMPRESSOR CLUTCH CIRCUIT DIAGNOSIS (2 OF 3) MANUAL A/C-HEATER

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks for ignition voltage on circuit No. 639 and PCM control of ground circuit No. 459 to A/C compressor clutch relay coil.
2. Checks for ignition voltage on circuit No. 639 to A/C compressor clutch relay contacts.
3. Determines whether A/C compressor clutch relay, compressor clutch coil or circuitry is faulty.

Scheme 99

CHART C-10A, A/C COMPRESSOR CLUTCH CIRCUIT DIAGNOSIS (3 OF 3) MANUAL A/C-HEATER

Note. Test numbers refer to numbers on diagnostic chart.

1. Determines if PCM is turning A/C compressor clutch relay on due to a false A/C request signal.
2. Determines whether problem is in A/C control head and circuits No. 604 and 762 to pressure cycling switch, or circuit No. 204 and PCM.
3. Checks for circuit No. 59 shorted to battery voltage or a faulty A/C compressor clutch.
4. Determines if A/C compressor clutch relay is faulty or A/C compressor clutch relay control circuit No. 459 is grounded at all times.

Scheme 100

CHART C-10B, A/C COMPRESSOR CLUTCH CIRCUIT DIAGNOSIS (1 OF 3) AUTOMATIC A/C-HEATER

Powertrain Control Module (PCM) delays A/C compressor clutch engagement momentarily after A/C is turned on. This delay allows Idle Air Control (IAC) motor to adjust engine RPM before A/C compressor clutch engages. PCM also disengages A/C compressor clutch during Wide Open Throttle (WOT). A/C compressor clutch is energized when PCM grounds circuit No. 459. PCM may engage A/C compressor clutch during engine cranking.

Note. Test numbers refer to numbers on diagnostic chart.

1. Determines whether or not PCM recognizes the A/C request signal.
2. Checks for an open high pressure cut-out switch.
3. Ensures that A/C-heater control programmer is supplying the A/C request signal.

Scheme 101

Scheme 102

CHART C-10B, A/C COMPRESSOR CLUTCH CIRCUIT DIAGNOSIS (2 OF 3) AUTOMATIC A/C-HEATER

Note. Test numbers refer to numbers on diagnostic chart.

1. Determines whether A/C relay can be controlled by PCM.
2. Checks for ignition voltage to A/C relay contacts.
3. Determines whether problem is caused by A/C relay, relay connections, compressor clutch or compressor clutch circuit is at fault.

Scheme 103

CHART C-10B, A/C COMPRESSOR CLUTCH CIRCUIT DIAGNOSIS (3 OF 3) AUTOMATIC A/C-HEATER

Note. Test numbers refer to numbers on diagnostic chart.

1. Determines if PCM is turning A/C compressor clutch relay on due to a false A/C request signal.
2. Isolates problem to A/C control head and circuits No. 66 and 604 to pressure cycling switch, or circuit No. 204 and PCM.
3. Checks for circuit No. 59 shorted to battery voltage or a faulty A/C compressor clutch.
4. Determines if A/C compressor clutch relay is faulty or A/C compressor clutch relay control circuit No. 459 is grounded all the time.

Scheme 104

Scheme 105

Scheme 106

3.8L (VIN K, L & 1) PCM Wiring Diagram (1 Of 3). Scheme 107

3.8L (VIN K, L & 1) PCM Wiring Diagram (2 Of 3). Scheme 108

3.8L (VIN K, L & 1) PCM Wiring Diagram (3 Of 3). Scheme 109

See also:
• BASIC TESTING
• TESTS W/CODES
• SENSOR RANGE CHARTS
• ADJUSTMENTS
• TESTS W/O CODES
• ENGINE COOLING FAN
• WIRING DIAGRAMS
• MISCELLANEOUS CONTROLS
• INTAKE AIR TEMPERATURE (IAT) SENSOR
• ENGINE SENSORS & SWITCHES