Engine Controls - System/component Tests 3.8l Buick Riviera VIII

INTRODUCTION

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

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.

Note. 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 HOW TO USE THE ENGINE PERFORMANCE SECTION in this section.

A & C CHART REFERENCE TABLE

GENERAL MOTORS A & C CHART REFERENCE

Boost Control Solenoid (VIN 1)

1. Install Tech 1 scan tool. Disconnect boost control solenoid harness connector. Turn ignition on, with engine off. Connect test light between boost control solenoid harness connector terminal "A" (Pink wire) and ground. Refer to appropriate wiring diagram in WIRING DIAGRAMS article. Test light should illuminate. If test light illuminates, go to step 3). If test light does not illuminate, go to next step.
2. Check 20-amp oxygen sensor fuse, located in instrument panel fuse/relay block. 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. Repair as necessary.
3. Connect test light between boost control solenoid harness connector terminals "A" (Pink wire) and "B" (Gray wire). 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 connector. Turn ignition on. If test light illuminated, check for shorted circuit between PCM terminal C1-23 and boost control solenoid terminal "B". If test light did not illuminate, replace PCM.
5. Using Tech 1 scan tool, select boost control output test under miscellaneous tests. Turn on boost control solenoid using Tech 1 scan tool. 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 test light to battery positive. Using test light, backprobe PCM terminal C1-23 (Gray wire). Turn on boost control solenoid using Tech 1 scan tool. If test light illuminated, check for open in circuit between PCM terminal C1-23 and boost control solenoid terminal "B". 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 tool, turn off boost control solenoid. Observe vacuum gauge. Vacuum reading should be about 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 PCM ground terminals. Use appropriate wiring diagram in WIRING DIAGRAMS article 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 voltmeter lead to a good ground. Touch positive voltmeter lead to each ground terminal. With vehicle running, voltmeter should indicate less than one volt. If 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 PCM constant battery power terminals and ground. If battery voltage is not present, check PCM power supply fuse. If fuse is okay, check for open in power supply or PCM wiring.
2. Turn ignition switch to the ON position. Using a voltmeter, check for battery voltage between PCM 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 PCM, or check for a defective ignition switch.
3. Connect voltmeter between ground and PCM start (crank) signal terminal. Turn ignition switch to the START position. Battery voltage should be present between PCM 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 PCM, or check for a defective ignition switch.

ENGINE SENSORS & SWITCHES

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

A/C ON (A/C Request) Switch Test

1. Start engine and allow to idle. If a scan tool 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 tool is not available or scan status does not change, measure voltage between ground and PCM A/C request terminal. For wiring schematics, see appropriate WIRING DIAGRAMS article.
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. For wiring schematics, see appropriate WIRING DIAGRAMS article.

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 appropriate WIRING DIAGRAMS article.

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. See testing procedures in TESTS W/CODES article.

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. To diagnose crankshaft position sensor, the following procedures can be used

1. If a scan tool is available, scan RPM parameter while cranking engine. If RPM is indicated, crankshaft position sensor is operating properly.
2. If scan tool 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. On all engines, 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. 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 table.

ECT SENSOR RESISTANCE VALUES (1)

ENGINE OIL LEVEL SENSOR

1. Diagnose and clear any diagnostic trouble code first. If code(s) is not present, go to next step.
2. Ensure engine oil level is up to full mark on dipstick. Ensure "Low Oil" light circuit is not faulty. If circuit is okay, go to next step.
3. Disconnect engine oil level sensor connector. Turn ignition on. Using a test light connected to ground, probe ignition feed circuit (Pink wire) at sensor harness connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 10).
4. Connect test light between ignition feed and ground circuit at oil level sensor harness connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 10).
5. Using a voltmeter, check voltage between engine oil level input circuit and ground. Battery voltage should be present. If battery voltage is present, go to next step. If battery voltage is not present, go to step 8).
6. Turn ignition off. Reconnect oil level sensor connector. Disconnect PCM connector. Connect voltmeter between engine oil level input circuit (Brown wire) and battery positive. Observe voltage while turning ignition on. If battery voltage is present for at least 2 seconds, go to step 11). If battery voltage is not present, go to next step 8).
7. Turn ignition off. Disconnect PCM connector. Turn ignition on. Check engine oil level sensor input circuit (Brown wire) for an open or shorted circuit. If circuit is open or shorted, go to step 14). If circuit is okay, go to step 12).
8. Disconnect engine oil level sensor. Check engine oil level input circuit for short to power. If circuit is shorted, go to step 14). If circuit is not shorted, check for poor connection at PCM or oil level sensor connector, or damaged wiring harness.
9. Locate and repair open in ignition feed circuit to oil level sensor. After repairs, go to step 14).
10. Locate and repair open in ground circuit to oil level sensor. After repairs, go to step 14).
11. Replace engine oil level sensor and proceed to step 14).
12. Check for poor connections at PCM. Repair as necessary and proceed to step 14). If connections are okay, go to next step.
13. Replace PCM and proceed to next step.
14. Turn ignition on. Observe "Low Oil" level light. If "Low Oil" light stays on for more than 3 seconds after ignition is turned on, repeat step 2).

FUEL TANK VAPOR PRESSURE SENSOR

Fuel tank vapor pressure sensor is located on fuel sending unit. Using DVOM, check resistance between sensor terminals. Resistance should be 90 ohms with fuel tank full or zero ohms with fuel tank empty.

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. 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 table. After vehicle has sat overnight, IAT 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 any trouble codes are present, see TESTS W/CODES article.

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

1. A malfunction in the MAP sensor circuit should set a related Diagnostic Trouble Code (DTC) in PCM memory. If a DTC is present, see TESTS W/CODES article. An out-of-calibration sensor may not set DTC. 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 28) If driveability condition improves, replace MAP sensor.
2. With ignition on and engine off, check MAP sensor parameter using a scan tool connected to Data Link Connector (DLC). Voltage should be as specified. See «MAP SENSOR VOLTAGE RANGE»(/buick/riviera/viii-1994-1999/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-38l) table. 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 28

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 DTC P0101 in TESTS W/CODES article. 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.

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 article.

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

1. Disconnect PNP switch harness connector. Connect ohmmeter between the PNP switch terminals. (Scheme 29) 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 29

POWER STEERING PRESSURE (PSP) SWITCH

1. If scan tool 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 tool 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 battery 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 30) 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 appropriate ADJUSTMENTS article.

A malfunction in the TP sensor circuit should set a related Diagnostic Trouble Code (DTC). For further information, see TESTS W/CODES article.

Scheme 30

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 TESTS W/CODES article for diagnosis.

Idle Air Control (IAC) Motor

See IDLE CONTROL SYSTEM (C-2) .

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 .

EGR Control Solenoid

See EMISSION SYSTEMS & SUB-SYSTEMS .

FUEL DELIVERY

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

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.

Fuel Pump Relay (A-5)

1. Disconnect fuel pump relay connector. Apply battery voltage and ground to fuel pump relay winding terminals. To identify fuel pump relay terminals, see appropriate wiring diagram in WIRING DIAGRAMS article.
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.

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 31) 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/riviera/viii-1994-1999/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-38l). (Scheme 35)& (Scheme 36).
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 31

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 table.

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 tool.
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/riviera/viii-1994-1999/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-38l) chart. If fuel pressure range is not as specified, see BASIC FUEL SYSTEM CHECKS in BASIC TESTING article.
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 article.
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 article.

FUEL PRESSURE RANGE CHART

Injector Leak Test

1. Turn engine off. Relieve fuel pressure. Access fuel injector harness connector. 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/riviera/viii-1994-1999/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-38l) table or INJECTOR BALANCE TEST (C2 - ALL MODELS).
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 .

1. Disconnect harness connector to motor. Check resistance across IAC coil terminals "A" and "B" (coil "B") and "C" and "D" (coil "A"). (Scheme 32) 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 noid light, or a scan tool capable of cycling PCM output devices (General Motors Tech 1).

Scheme 32

IGNITION SYSTEM

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

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 article.

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 tool is available, connect it to the DLC. Tap on engine next to knock sensor and note "knock" parameter. Knock should be indicated on scan tool.
3. If a scan tool 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/riviera/viii-1994-1999/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-38l__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 tool is available, connect it to the DLC. Tap on engine next to knock sensor and note "knock" parameter. Knock should be indicated on scan tool.
3. If scan tool 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/riviera/viii-1994-1999/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-38l__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 table.

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.

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.

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.

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 (DTC). 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 K - SENSOR RANGE CHARTS article.

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 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, replace instrument cluster.
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.

Converter Clutch Solenoid

Disconnect harness connector to Torque Converter Clutch (TCC) solenoid. Solenoid resistance should be 10-15 ohms. On all other models, measure resistance between appropriate TCC solenoid terminals. (Scheme 33) 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 33)

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 appropriate converter clutch harness terminals. Start engine and place transmission in Drive. Accelerate vehicle to 45 MPH and note test light.
3. If test light is off, 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.

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 33) Accelerate vehicle to 45 MPH and note test light. If test light does not illuminate, problem is a faulty PCM connector or PCM.

Converter Clutch Schematic. Scheme 33

Warning Light Diagnosis

1. Perform On-Board Diagnostics (OBD) System check. See BASIC TESTING article. After performing OBD system check, go to next step.
2. Check instrument cluster. See INSTRUMENT PANEL article in the ACCESSORIES/SAFETY EQUIPMENT section. If instrument panel is okay, go to next step.
3. Turn ignition off. Disconnect PCM connector. Turn ignition on. Using a DVOM, check voltage between affected PCM output circuit at PCM harness connector terminal and ground. See appropriate WIRING DIAGRAMS article. Battery voltage should be present. If battery voltage is present, go to next step. If battery voltage was not present, go to step 7).
4. Set DVOM to 10-amp scale. Check current between affected PCM output circuit and ground. Monitor reading for about 2 minutes. DVOM should read .05-1.50 amps. If reading is as specified, go to step 12). If reading is not as specified, go to next step.
5. Disconnect instrument panel cluster, but leave PCM connector disconnected. Using DVOM, check voltage between affected PCM output circuit and ground. DVOM should read zero volts. If voltage reading is as specified, go to step 15). If voltage reading is not as specified, go to next step.
6. Locate and repair short to voltage in affected PCM output circuit. After repairs, go to step 17).
7. Check ignition feed fuse for instrument panel cluster indicator lights. If fuse is blown, go to next step. If fuse is okay, go to step 9)
8. Locate and repair short to ground in ignition feed circuit for instrument panel cluster indicator lights. Replace fuse and go to step 17).
9. Disconnect instrument cluster connector. Turn ignition on. Check voltage between ignition feed circuit for instrument panel cluster indicator lights and ground. Battery voltage should be present. If battery voltage is present, go to next step. If battery voltage was not present, go to step 14).
10. Check affected PCM output circuit for an open or shorted circuit to ground. If circuit is open or shorted, go to step 17). If circuit was okay, go to next step.
11. Check affected PCM output circuit and ignition feed circuit for poor connection at instrument panel cluster and at PCM. If problem is present, repair as necessary and then go to step 17). If problem was not found, go to step 15).
12. Turn ignition off. Reconnect PCM harness connector. Disconnect instrument cluster connector. Turn ignition on. Connect a test light between affected PCM output circuit and ignition feed circuit at instrument panel harness connector. Using a scan tool, perform "Outputs Test" function to cycle affected warning light on and off. If test light flashes on and off, check for shorted component or circuit in the output driver circuit. Check for faulty instrument cluster. If test light does flash on and off, go to next step.
13. Check affected PCM output circuit for poor connection to PCM. Replace defective terminal and then go to step 17). If terminal is okay, go to step 16).
14. Repair open in ignition feed circuit to instrument panel cluster indicator lights. After repairs, go to step 17).
15. Replace instrument cluster and then go to step 17).
16. Replace PCM and then go to next step.
17. Using scan tool, operate affected warning light. If warning light does not operate properly, go to step 3).

A/C CLUTCH (C-10)

Note. For specific A/C clutch system diagnosis, see C-10 & C-12 DIAGNOSTIC TESTS .

1. Disconnect A/C clutch relay harness connector. See A/C COMPRESSOR CLUTCH RELAY LOCATION table. Using proper wiring diagram and an ohmmeter, check continuity between A/C clutch relay winding terminals. See appropriate WIRING DIAGRAMS article. 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.

A/C COMPRESSOR CLUTCH RELAY LOCATION

ELECTRIC COOLING FAN (C-12)

Note. For specific A/C clutch system diagnosis, see C-10 & C-12 DIAGNOSTIC TESTS .

Cooling Fan System

1. Connect a test light to battery voltage. Probe test light to cooling fan control driver terminal of PCM. (Scheme 34) 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 ignition on and engine off will cause PCM to activate 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. See «COOLING FAN RELAY LOCATION»(/buick/riviera/viii-1994-1999/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-38l) table for specific vehicle relay location. Using an ohmmeter, check continuity of relay winding. See WIRING DIAGRAMS . 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.

COOLING FAN RELAY LOCATION

Cooling Fan Circuit Wiring Diagram. Scheme 34

C-10 & C-12 DIAGNOSTIC TESTS

Note. For a more specific system testing, refer to the following C-10 and C-12 diagnostic tests. If any test other than a C-10 or C-12 test is referenced, see TESTS W/CODES article.

Description

When A/C is selected a 12-volt signal is supplied to A/C request input of PCM. A/C compressor clutch relay is controlled through PCM. PCM monitors A/C refrigerant pressure. If A/C refrigerant pressure, and engine operating conditions are within a specific calibrated acceptable range, PCM will enable A/C compressor relay. This is done by providing a ground path for A/C relay coil within PCM. When A/C compressor relay is enabled, battery voltage is supplied to compressor clutch coil.

PCM will enable A/C compressor clutch whenever engine is running and A/C has been requested, unless throttle is greater than 90 percent, A/C head pressure is greater than 414 psi (29.1 kg/cm 2 ) or 4.27 volts, or less than 34 psi (2.3 kg/cm 2 ), or .35 volt as determined by A/C refrigerant pressure sensor, ignition voltage less than 10.5 volts, engine speed greater than 4500 RPM for 5 seconds, engine coolant temperature greater than 257°F (125°C), and intake air temperature less than 41°F (5°C).

Compressor Clutch Control Circuit Diagnosis

1. Perform On-Board Diagnostics (OBD) System check. See BASIC TESTING article. After performing OBD system check, go to next step.
2. Check if any PCM or Heating, Ventilation or A/C (HVAC) Diagnostic Trouble Codes (DTCs) have been present. If any DTCs are present, diagnose that code first. See TESTS W/CODES article. If no DTCs are present, go to next step.
3. Ensure intake air temperature is greater than 60°F (15°C). Ensure engine coolant temperature is less than 246°F (119°C). Turn A/C off. Start and idle engine. Observe A/C compressor. If A/C compressor clutch is engaged, go to step 21). If A/C compressor clutch is not engaged, go to next step.
4. Run engine at 1000-1500 RPM. Select DEFROST or MAX mode on A/C control head. Observe A/C compressor. If A/C compressor clutch is engaged, system is operating correctly. Problem may be intermittent. If A/C compressor clutch is not engaged, go to next step.
5. With DEFROST or MAX mode still selected, observe A/C REQUEST display on scan tool. If A/C REQUEST displays YES, go to step 9). If A/C REQUEST does not display YES, go to next step.
6. Turn ignition off. Disconnect PCM. Turn ignition on. With DEFROST or MAX mode still selected, measure voltage on A/C request circuit at PCM harness connector (Dark Green/White wire). If battery voltage is present, go to step 8). If battery voltage is not present, go to next step.
7. Check A/C request circuit (Dark Green/White wire) for an open, short to ground, or poor connection at A/C control head. If a problem was found, diagnose A/C control. If a problem is not found, go to step 37).
8. Check A/C request circuit (Dark Green/White wire) for a poor connection at PCM. If a repair was made, go to step 37). If a repair was not made, go to step 35).
9. Observe A/C refrigerant pressure sensor display on scan tool. If indicated pressure is .35-4.27 volts, go to step 12). If indicated pressure is not .35-4.27 volts, go to next step.
10. Connect Manifold Gauge Set (J 39183-C). Observe high side refrigerant pressure on gauge. If high side refrigerant pressure is within 34-414 psi (2.3-29 kg/cm 2 ), go to next step. If high side refrigerant pressure is not within 34-414 psi (2.3-29 kg/cm 2 ), charge A/C system.
11. Turn ignition off. Disconnect PCM and A/C refrigerant pressure sensor. Measure resistance of following circuits between PCM and A/C refrigerant pressure sensor: Refrigerant pressure sensor signal circuit (Red/Black wire). 5-volt reference "B" circuit (Gray wire). Sensor ground circuit (Black wire). If any resistance is higher than 5 ohms, locate and repair cause of high resistance in circuit as necessary, then go to step 37). If any resistance is not higher than 5 ohms, go to step 18).
12. Disconnect A/C relay electrical connector. Probe ignition feed circuits (Orange and Dark Green wires) at A/C relay harness connector with a test light to ground. If test light illuminates, go to next step. If test light does not illuminate, go to step 31).
13. Connect a fused jumper between ignition feed circuit and A/C compressor clutch control circuit (Dark Green wire) at A/C relay connector. If A/C compressor clutch engages, go to step 14). If A/C compressor clutch does not engage, go to step 15).
14. Check for poor connections at A/C relay. If a repair was made, go to step 37). If a repair was not made, go to step 32).
15. Disconnect A/C compressor clutch electrical connector (leave ignition feed circuit and A/C compressor clutch control circuit jumpered at A/C relay connector). Connect a test light between A/C compressor clutch control circuit (Dark Green wire) and compressor ground circuit (Black wire). If test light illuminates, go to next step. If test light does not illuminate, go to step 17).
16. Check for poor connections at A/C compressor clutch. If a repair was made, go to step 37). If a repair was not made, go to step 33).
17. Check for an open or short to ground in A/C compressor clutch control circuit (Dark Green wire). If a repair was made, go to step 37). If a repair was not made, go to step 34).
18. Leave PCM and A/C refrigerant pressure sensor disconnected at PCM. Turn ignition on. Measure voltage between A/C refrigerant pressure signal circuit (Red/Black wire) and ground. If voltage is about zero volts, go to next step. If voltage is not about zero volts, go to step 20).
19. Check the following: 5-volt reference "B" circuit (Gray wire) for a poor connection at PCM. 5-volt reference "B" circuit (Gray wire) for a poor connection at refrigerant pressure sensor. Refrigerant pressure signal circuit (Red/Black wire) for a poor connection at PCM. Refrigerant pressure signal circuit (Red/Black wire) for a poor connection at refrigerant pressure sensor. Sensor ground circuit (Black wire) for a poor connection at refrigerant pressure sensor. If a problem is found, repair as necessary and go to step 37). If a problem was not found, go to step 36).
20. Locate and repair short to voltage in A/C refrigerant pressure signal circuit (Red/Black wire). Go to step 37).
21. Turn ignition on. Turn A/C off. Observe A/C REQUEST on scan tool. If A/C REQUEST displays YES, go to next step. If A/C REQUEST does not display YES, go to step 24).
22. Turn ignition off. Disconnect PCM. Turn ignition on, A/C off. Measure voltage between A/C request circuit (Dark Green/White wire) at PCM harness connector and ground. If voltage measures near battery voltage, go to next step. If voltage does not measure near battery voltage, go to step 35).
23. Turn ignition off. Disconnect A/C control head/programmer. Turn ignition on. Check A/C request circuit (Dark Green/White wire) for a short to voltage. If a problem was found and a repair was made, go to step 37). If a problem was not found, diagnose A/C controls.
24. Disconnect A/C relay. Start vehicle and observe A/C compressor. If A/C compressor clutch is engaged, go to step 29). If A/C compressor clutch is not engaged, go to next step.
25. Probe A/C compressor clutch control circuit (Dark Green wire) at A/C relay harness connector with a test light to ground. If test light illuminates, go to step 27). If test light does not illuminate, go to next step.
26. Replace A/C relay. Go to step 37).
27. Turn ignition off. Disconnect PCM. Probe A/C relay driver circuit (Dark Green/White wire) at PCM connector with a test light connected to battery voltage. If test light illuminates, go to next step. If test light does not illuminate, go to step 35).
28. Repair short to ground in A/C compressor clutch relay driver circuit (Dark Green/White wire). Go to step 37).
29. Turn ignition off. Disconnect A/C compressor clutch electrical connector. Start engine and observe A/C compressor. If A/C compressor clutch is engaged, go to step 33). If A/C compressor clutch is not engaged, go to next step.
30. Locate and repair short to voltage in A/C compressor clutch control circuit (Dark Green wire). Go to step 37).
31. Repair open or short to ground in ignition feed circuit (Pink wire) to A/C compressor relay. Go to step 37).
32. Replace A/C compressor relay. Go to step 37).
33. Repair A/C compressor clutch. Go to step 37).
34. Locate and repair open in A/C compressor clutch ground circuit (Black wire). Go to step 37).
35. Replace PCM. Go to step 37).
36. Replace A/C refrigerant pressure sensor. Go to step 37).
37. Ensure intake air temperature is greater than 60°F (15°C). Ensure engine coolant temperature is less than 246°F (119°C). With A/C off, start and idle engine. Observe A/C compressor. If clutch is engaged, go to step 21). If clutch is not engaged, go to next step.
38. Run engine at 1000-1500 RPM. Select DEFROST or MAX mode on control head. Observe A/C compressor. If A/C compressor clutch is engaged, system is okay. If A/C compressor clutch is not engaged, go to step 5).

Power for fan motors comes from a fusible link at battery junction block. Relays are energized when current flows from FANS/ACTUATOR fuse through relay coils to ground through PCM. PCM Output Driver Module (ODM) "B" output No. 1 is grounded for low speed fan operation. PCM ODM "B" outputs No. 1 and 2 are grounded for high speed operation.

During low speed fan operation PCM supplies a ground path for low speed relay No. 1 through ODM "B" output No. 1. This closes low speed relay contacts and current flows from battery junction block through relay and to primary cooling fan. Only ground path for primary cooling fan is through series/parallel relay, and secondary fan motor. Result is a series circuit with both fans running at low speed.

During high speed fan operation, PCM supplies a ground path for low speed fan relay through ODM "B" output No. 1. PCM also supplies a ground path for high speed relay No. 3 and series/parallel relay No. 2 through ODM "B" output No. 2. This closes all 3 fan relays. At high speed, primary and secondary cooling fans are both supplied current from battery junction block and each fan has its own ground path.

Cooling Fan Circuit Diagnosis

1. Perform On-Board Diagnostics (OBD) System check. See BASIC TESTING article. After performing OBD system check, go to next step.
2. Check if any Diagnostic Trouble Codes (DTCs) are present. If DTCs are present, see TESTS W/CODES article. If no DTCs are present, go to next step.
3. Ensure engine coolant temperature is less than 212°F (100°C). Turn A/C off. Start and run engine. If cooling fan operate, go to step 24). If cooling fans do not operate, go to next step.
4. Using scan tool OUTPUT TESTS, command fan No. 1 on. If both fans run at low speed, go to next step. If both fans do not run at low speed, go to step 8).
5. Using scan tool OUTPUT TESTS, command fan No. 2 on. If both fans run at high speed, go to next step. If both fans do not run at high speed, go to step 53).
6. Ensure ambient temperature is greater than 60°F (15°C). Exit scan tool OUTPUT TESTS. Start and run engine. Turn A/C on. If fans come on, system is operating correctly. Problem may be intermittent. If fans do not come on, go to next step.
7. Using scan tool, view A/C REQUEST. If scan tool displays YES, go to step 75). If scan tool does not display YES, diagnose A/C clutch control circuit.
8. Disconnect low speed cooling fan relay No. 1 electrical connector. Using a test light connected to ground, probe harness connector terminal No. 30 (Red wire). If test light illuminates, go to step 10). If test light does not illuminate, go to next step.
9. Repair open circuit in battery feed circuit to low speed cooling fan relay No 1, terminal No. 30 (Red wire). Go to step 77).
10. Turn ignition on. Using a test light connected to ground, probe low speed cooling fan relay harness connector terminal No. 85 (Brown wire). If test light illuminates, go to step 12). If test light does not illuminate, go to step 11).
11. Locate and repair open in feed circuit to low speed cooling fan relay terminal No. 85 (Brown wire). Go to step 77).
12. Disconnect both cooling fans. Jumper terminals "A" (White or Black wire) and "B" (Light Blue or Black wire) together at both cooling fan connectors. Connect a test light between low speed cooling fan relay harness connector terminals No. 30 (Red wire) and No. 87 (Light Blue wire). If test light illuminates, go to next step. If test light does not illuminate, go to step 19).
13. Connect a test light between low speed cooling fan relay harness connector terminals No. 86 (Dark Green wire) and No. 85 (Brown wire). Turn ignition on. Using scan tool OUTPUT TESTS, activate fan No. 1. If test light illuminates, go to next step. If test light does not illuminate, go to step 17).
14. Turn ignition off. Remove jumper wires from cooling fan connectors and reconnect fans. Install a fused jumper wire between low speed cooling fan relay harness connector terminals No. 30 (Red wire) and No. 87 (Light Blue wire). Turn ignition on. If fans come on, go to next step. If fans do not come on, go to step 16).
15. Check for poor connections at low speed cooling fan relay. If a repair was made, go to step 77). If a repair was not made, go to step 29).
16. Check for poor connection at primary or secondary fan motors. If a repair was made, go to step 77). If a repair was not made, go to step 19).
17. Turn ignition off. Disconnect PCM Blue connector. Install a fused jumper between low speed cooling fan relay harness connector terminals No. 85 (Brown wire) and No. 86 (Dark Green wire). Turn ignition on. Probe PCM connector terminal C1-32 (Dark Green wire) with a test light to ground. If test light illuminates, go to step 69). If test light does not illuminate, go to next step.
18. Repair open in fan No. 1 (low speed) driver circuit (Dark Green wire) between PCM and low speed cooling fan relay. Go to step 77).
19. Turn ignition off. Remove jumpers from cooling fan connectors and reconnect fans. Install a fused jumper wire between low speed cooling fan relay harness connector terminals No. 30 (Red wire) and No. 87 (Light Blue wire). Remove series/parallel cooling fan relay No. 2 from underhood electrical center. Connect a test light to ground and probe series/parallel cooling fan relay No. 2 harness connector terminal No. 30 (White wire) in underhood electrical center. If test light illuminates, go to next step. If test light does not illuminate, go to step 23).
20. Connect test light between series/parallel relay No. 2 harness connector terminals No. 87A (Purple wire) and No. 30 (White wire) in underhood electrical center. If test light illuminates, go to step 22). If test light does not illuminate, go to next step.
21. Check for an open in Purple wire between series/parallel cooling fan relay No. terminal 87A in underhood electrical center and secondary fan terminal "B" (Light Blue wire). If a repair was made, go to step 77). If a repair was not made, go to step 52).
22. Check for poor connection at series/parallel cooling fan relay No. 2. If a repair was made, go to step 77). If a repair was not made, go to step 67).
23. Check for an open circuit in Light Blue wire between low speed cooling fan relay terminal No. 87 and underhood electrical and primary fan terminal "A". If a repair was made, go to step 77). If a repair was not made, go to step 51).
24. Using scan tool, view A/C REQUEST. If scan tool displays YES, perform A/C clutch circuit diagnosis. If scan tool does not display YES, go to next step.
25. If cooling fans are operating at low speed, go to step 26). If cooling fans are not operating at low speed, go to step 32).
26. Disconnect low speed cooling fan relay electrical connector. If fans are on, go to step 27). If fans are not on, go to step 28).
27. Repair short to voltage in Light Blue wire. Go to step 77).
28. Using a test light connected to voltage, probe low speed cooling fan relay harness connector terminal No. 86 (Dark Green wire). If test light illuminates, go to step 30). If test light does not illuminate, go to next step.
29. Replace low speed cooling fan relay. Go to step 77).
30. Turn ignition off. Disconnect PCM Blue connector. Using a test light connected to voltage, probe low speed cooling fan relay harness connector terminal No. 86 (Dark Green wire). If test light illuminates, go to next step. If test light does not illuminate, go to step 75).
31. Locate and repair short to ground in fan No. 1 (low speed) driver circuit (Dark Green wire). Go to step 77).
32. Using scan tool OUTPUT TESTS function, command fan No. 1 on. If both fans run at high speed, go to next step. If both fans do not run at high speed, go to step 44).
33. Using scan tool, view A/C refrigerant pressure signal circuit. If scan tool indicates less than 1.2 volt, go to next step. If scan tool indicates 1.2 volt or more, go to step 36).
34. Turn ignition off. Disconnect PCM. Turn ignition on and observe cooling fan operation. If both fans operate at high speed, go to next step. If both fans do not operate at high speed, go to step 75).
35. Locate and repair short circuit to ground in Dark Green and Dark Blue wires. Go to step 77).
36. Turn ignition off. Disconnect A/C refrigerant pressure sensor. Turn ignition on. Using scan tool, view A/C PRESSURE. If scan tool displays about zero volts, go to step 38). If scan tool does not display about zero volts, go to next step.
37. Probe A/C refrigerant pressure signal circuit with a voltmeter connected to A/C refrigerant pressure sensor ground. If scan tool displays about zero volts, go to step 69). If scan tool does not display about zero volts, go to step 43).
38. Probe A/C refrigerant pressure sensor ground with a test light to voltage. If test light illuminates, go to next step. If test light does not illuminate, go to step 41).
39. Probe A/C refrigerant pressure sensor 5-volt reference with a voltmeter connected to A/C refrigerant pressure sensor ground. If scan tool displays about 5 volts, go to next step. If scan tool does not display about 5 volts, go to step 42).
40. Replace A/C refrigerant pressure sensor. Go to step 77).
41. Locate and repair open or short to ground in A/C refrigerant pressure sensor ground circuit. Go to step 77).
42. Locate and repair open or short to ground in A/C refrigerant pressure sensor 5-volt reference circuit. Go to step 77).
43. Locate and repair short to voltage in A/C refrigerant pressure signal circuit. Go to step 77).
44. If secondary fan motor is running at high speed go to step 46). If secondary fan is not running at high speed, go to next step.
45. Replace secondary fan motor. Go to step 77).
46. Turn ignition off. Remove high speed cooling fan relay No. 3 from underhood electrical center. Turn ignition on. Using scan tool output controls function, command fan No. 1 on. Observe fan function. If secondary fan is running at high speed, go to next step. If secondary fan is not running at high speed, go to step 72).
47. Disconnect low speed cooling fan relay No. 1. If secondary fan is running at high speed, go to next step. If secondary fan is not running at high speed, go to step 71).
48. Remove series/parallel cooling fan relay No. 2 from underhood electrical center. If secondary fan is running at high speed, go to next step. If secondary fan is not running at high speed, go to step 50).
49. Locate and repair short to voltage in Purple wire. Go to step 77).
50. Locate and repair short to voltage in Red wire. Go to step 77).
51. Locate and repair open in White or Red wire between series/parallel cooling fan relay No. 2 terminal No. 30 in underhood electrical center and primary fan terminal "B". Go to step 77).
52. Locate and repair open in Black ground wire between secondary fan terminal "A" and ground. Go to next step.
53. Go to step 77).
54. Remove high speed cooling fan relay No. 3 from underhood electrical center. Install test light between high speed cooling fan relay terminal No. 86 (Dark Blue wire) and voltage. Turn ignition on. Using scan tool, command relay No. 2 on. If test light illuminates, go to step 57). If test light does not illuminate, go to next step.
55. Remove series/parallel cooling fan relay No. 2 from underhood electrical center. Install test light between series/parallel cooling fan relay No. 2 terminal No. 86 (Dark Blue wire) and voltage. Turn ignition on. Using a scan tool, command relay No. 2 on. If test light illuminates, go to step 76). If test light does not illuminate, go to next step.
56. Turn ignition off. Disconnect PCM. Turn ignition on. Check Dark Blue wire for an open or short to voltage between series/parallel cooling fan relay and PCM. If a repair was made, go to step 77). If a repair was not made, go to step 75).
57. Turn ignition off. Reinstall high speed cooling fan relay No. 3. Disconnect both fan electrical connectors. Turn ignition on. Using scan tool, command relay No. 2 on. Probe terminal "B" (Purple wire) at secondary fan connector with a test light to ground. If test light illuminates, go to next step. If test light does not illuminate, go to step 60).
58. Turn ignition off. Reinstall series/parallel cooling fan relay No. 2. Disconnect both fan electrical connectors. Turn ignition on. Using scan tool, command relay No. 2 on. Probe terminal "A" (Red wire) at primary fan connector with a test light to voltage. If test light illuminates, go to next step. If test light does not illuminate, go to step 67).
59. Replace affected fan motor. Go to step 77).
60. Remove high speed cooling fan relay No. 3. Turn ignition on. Using a test light connected to ground, probe high speed cooling fan relay terminal No. 85 (Brown wire). If test light illuminates, go to step 62). If test light does not illuminate, go to next step.
61. Locate and repair open in ignition feed circuit to high speed cooling fan relay. Go to step 77).
62. Using a test light connected to ground, probe high speed cooling fan relay terminal No. 87 (Red wire). If test light illuminates, go to step 64). If test light does not illuminate, go to next step.
63. Locate and repair open in battery feed circuit to high speed cooling fan relay. Go to step 77).
64. Check wiring for an open circuit between secondary fan terminal "B" (Light Blue wire) and high speed cooling fan relay terminal No. 30 (Purple wire). If a repair was made, go to step 77). If a repair was not made, go to next step.
65. Check for poor terminal connections at high speed cooling fan relay. If a repair was made, go to step 77). If a repair was not made, go to next step.
66. Replace high speed cooling fan relay. Go to step 77).
67. Remove series/parallel cooling fan relay No. 2. Turn ignition on. Using a test light connected to ground, probe series/parallel relay No. 2, terminal No. 85 (Brown wire). If test light illuminates, go to step 69). If test light does not illuminate, go to next step.
68. Locate and repair open in ignition feed circuit to series/parallel cooling fan relay No. 2. Go to step 77).
69. Using a test light connected to ground, probe series/parallel cooling fan relay No. 2, terminal No. 87 (Black wire). If test light illuminates, go to step 71). If test light does not illuminate, go to next step.
70. Locate and repair open in battery feed circuit to series/parallel cooling fan relay No. 2. Go to step 77).
71. Using a test light to voltage, probe series/parallel cooling fan relay No. 2, terminal No. 87 (Black wire). If test light illuminates, go to next step. If test light does not illuminate, go to step 73).
72. Locate and repair open in Black wire between primary fan terminal "A" and series/parallel cooling fan relay terminal No. 87. Go to step 77).
73. Check for poor terminal connections at series/parallel cooling fan relay No. 2. If a repair was made, go to step 77). If a repair was not made, go to next step.
74. Replace series/parallel cooling fan relay No. 2. Go to step 77).
75. Replace PCM. Go to step 77).
76. Repair open in Dark Blue wire between series/parallel cooling fan relay No. 2 and high speed cooling fan relay No. 3. Go to step 77).
77. Ensure coolant temperature is less than 212°F (100°C). Turn A/C off. Start and run engine. If cooling fans are running, go to step 24). If cooling fans are not running, go to next step.
78. Using scan tool OUTPUT TESTS function, activate fan relay No. 1. If both fans run at low speed, go to next step. If both fans do not run at low speed, go to step 8).
79. Using scan tool OUTPUT TESTS function, activate fan relay No. 2. If both fans runs at high speed, system is operating normally at this time. If both fans do not run at high speed, go to step 54).

Scheme 35

Scheme 36

See also:
• K - SENSOR RANGE CHARTS
• ENGINE SENSORS & SWITCHES
• FUEL SYSTEM
• IGNITION SYSTEM
• MISCELLANEOUS CONTROLS
• C-10 & C-12 DIAGNOSTIC TESTS