Engine Controls - System/component Tests - v8 Buick Roadmaster VIII

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.

A & C CHART REFERENCES

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 - USING THIS SECTION article in this section.

A & C CHART REFERENCE

BODY CODE IDENTIFICATION

BODY CODE IDENTIFICATION

Ground Circuits

1. Using an ohmmeter, check for continuity to ground on control unit ground terminals. Use appropriate wiring diagram in WIRING DIAGRAMS article to determine ECM 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 ECM 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/roadmaster/viii-1991-1996/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-v8__miscellaneous-controls) .
3. With A/C mode selector in the ON position, 12 volts should be present. If 12 volts are not present, check for open between A/C mode select switch and ECM 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 appropriate 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 step 2). 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/roadmaster/viii-1991-1996/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-v8__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 (C(3)I SYSTEM)

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

CAMSHAFT SENSOR (CADILLAC EXCEPT BROUGHAM)

See HALL EFFECT CAMSHAFT SENSOR .

COOLANT TEMPERATURE SENSOR (CTS)

If a coolant sensor-related diagnostic trouble code is present, see appropriate 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 coolant temperature sensor connector. Measure resistance between sensor terminals. Resistance should be high when engine is cold and drop as engine warms. See CTS RESISTANCE VALUES table.

CTS RESISTANCE VALUES

CRANKSHAFT SENSOR

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

To diagnose 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. 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 OIL TEMPERATURE SENSOR (CORVETTE)

1. If engine oil temperature sensor circuit malfunctions, a related diagnostic trouble code will be set. However, if sensor is out of calibration, this will not set a code. To check calibration, use the following method.
2. Disconnect engine oil temperature sensor connector. Using an ohmmeter, measure resistance between sensor terminals. Resistance should be as specified. See «ENGINE OIL TEMPERATURE SENSOR RESISTANCE»(/buick/roadmaster/viii-1991-1996/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-v8) table. Also see Code 52 and Code 62 in appropriate TESTS W/CODES article in this section.

ENGINE OIL TEMPERATURE SENSOR RESISTANCE

HALL EFFECT CAMSHAFT SENSOR (CADILLAC EXCEPT BROUGHAM)

1. Turn ignition off. Disconnect 3-terminal connector at distributor. Turn ignition on and verify presence of 12 volts on Pink wire of 3-terminal connector. Turn ignition off. Reconnect 3-wire connector.
2. Disconnect 6-terminal, 5-wire connector at HEI distributor. Connect a DVOM to terminal "E" (positive) and terminal "D" (negative) on distributor side of connector. (Scheme 36)
3. Turn ignition on and note DVOM reading. Using ignition key, bump starter to rotate distributor. Note DVOM reading. Repeat procedure several times. Depending upon distributor/Hall Effect switch window position, DVOM should read either zero or 12 volts. Reading should NOT remain constant as engine is bumped.
4. Crank engine and note voltage reading. Depending on voltmeter, reading may fluctuate rapidly between zero and 12 volts or average about 6 volts. If voltmeter readings are correct, Hall Effect switch is okay. If voltmeter readings are not correct, replace Hall Effect switch.

Scheme 36

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 appropriate 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 table. After vehicle has sat overnight, MAT sensor and coolant sensor should have close to the same resistance reading.

IAT SENSOR RESISTANCE

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. Also see Code 43 in appropriate 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 ECM memory. If a code is present, see appropriate 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. If driveability problems exist, MAP sensor failure is suspected and no MAP code is present, disconnect MAP sensor connector. (Scheme 37) If driveability condition improves, replace MAP sensor.
2. With ignition on and engine off, check MAP sensor parameter using a scan tester connected to the ALDL connector. Voltage should be as specified. See «MAP SENSOR VOLTAGE RANGE»(/buick/roadmaster/viii-1991-1996/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-v8) 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 37

MAP SENSOR VOLTAGE RANGE

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 appropriate TESTS W/CODES article in this section.

OXYGEN SENSOR

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 ECM 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 ECM. 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 appropriate TESTS W/CODES 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 38) 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 ECM.

Scheme 38

POWER STEERING PRESSURE (PSP) SWITCH (C-1)

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 12 volts on switch harness from ECM. If 12 volts are not present, check for open or short to ground in harness between switch connector and ECM.

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 39) 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 appropriate TESTS W/CODES article in this section.

Scheme 39

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 ECM memory. If a code is set, refer to appropriate TESTS W/CODES article in this section for diagnosis.

SECONDARY AIR ELECTRIC AIR PUMP (5.7L "F" BODY)

Locate secondary AIR electric air pump under ABS hydraulic modulator, on left front of engine compartment. Disconnect 3-wire connector from electric air pump. Apply ground to terminal "C" (Black wire) of pump. Apply battery voltage with a fused jumper wire to terminal "A" (Red wire) of pump. Pump should run. If pump does not run, replace pump.

SECONDARY AIR ELECTRIC AIR PUMP (5.7L "Y" BODY)

Locate secondary AIR electric pump on left front side of engine compartment, mounted on frame. Disconnect 2-wire connector from electric air pump. Apply ground to Black wire terminal of air pump. Apply battery voltage with fused jumper wire to Black/Orange wire terminal of air pump. Pump should run. If pump does not run, replace pump.

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 .

AIR BY-PASS VALVE SOLENOID

Note. All ECM-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.

See EMISSION SYSTEMS & SUB-SYSTEMS.

CANISTER PURGE SOLENOID

Note. All ECM-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.

See EMISSION SYSTEMS & SUB-SYSTEMS.

EGR CONTROL SOLENOID

Note. All ECM-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.

See EMISSION SYSTEMS & SUB-SYSTEMS.

REVERSE LOCK-OUT SOLENOID (5.7L "F" BODY)

Note. All ECM-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.

See MISCELLANEOUS CONTROLS .

FUEL DELIVERY

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

Fuel Pressure Regulator (PFI)

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.

Fuel Pressure Regulator (TBI)

Fuel pressure regulator is mechanically controlled by internal spring pressure. Regulator is adjusted at factory and is not serviceable. If fuel pressure is too low, check fuel filter, fuel pump pressure and volume. If fuel pressure is too high, check for restricted fuel tank return line. If no faults are found and pressure is too high or too low, replace fuel pressure regulator.

Fuel Pump Relay (A-5)

1. Disconnect fuel pump relay connector. See «COMPONENT LOCATIONS»(/buick/roadmaster/viii-1991-1996/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-v8) at the end of this 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 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 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 40) Turn ignition off. Disconnect fuel pump relay connector. 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/roadmaster/viii-1991-1996/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-v8) at end of this article. (Scheme 70)- see scheme 44.
2. 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 40

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 PFI INJECTOR BALANCE TEST below.

PFI 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 PFI INJECTOR BALANCE TEST should not be repeated more than once without starting and running engine.

1. With ignition off, connect Fuel Pressure Gauge (J-34730-1) to pressure tap. Unplug harness connector at all injectors. Connect Injector Tester (J-34730-3) to one of the injectors.
2. Follow manufacturer's instructions when installing adapter harness. Ignition should be turned off at least 10 seconds to complete ECM shutdown cycle.
3. Turn ignition on. Fuel pump should run at least 2 seconds after ignition is turned on. Bleed air from gauge and hose to ensure accurate gauge reading. Repeat this procedure until all air is bled from system. Turn ignition off for at least 10 seconds.
4. Turn ignition on again to bring fuel pressure to maximum. Record initial pressure reading. Energize tester one time and note pressure drop at lowest point.
5. Disregard any slight pressure drop after low point is reached. Subtracting second pressure reading from initial reading indicates amount of injector pressure drop.
6. Repeat step 4) on each injector and compare pressure drop. Recheck injectors not within pressure drop range. Replace injector(s) failing second check.
7. If injectors are all okay, plug in harness connectors and review SYMPTOMS in TESTS W/O CODES article in this section.

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 41) 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 ECM output devices (General Motors Tech 1).

Scheme 41

IDLE SPEED CONTROL (ISC) MOTOR (CADILLAC EXCEPT BROUGHAM)

A malfunction in the ISC circuit will set a diagnostic trouble code. For testing procedures, see appropriate TESTS W/CODES article in this section. Also, see ISC minimum and maximum adjustment procedures in ADJUSTMENTS article in this section.

IDLE SWITCH (CADILLAC EXCEPT BROUGHAM)

1. The ISC motor is equipped with an internal idle switch (also called a throttle or nose switch) which informs the ECM when it should be controlling idle.
2. Disconnect ISC connector. Connect an ohmmeter across Pink and Black/White wire terminals ("A" and "B") of ISC motor connector. (Scheme 42) With throttle closed, continuity should exist. With throttle open enough to relieve tension from the ISC plunger, continuity should not exist.

Scheme 42

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. On all vehicles, ground "test" terminal "B" of ALDL connector. (Scheme 43) A noticeable change in engine speed should occur. If no change occurs, see DIAGNOSTIC CIRCUIT CHECK in 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 ECM will set a related diagnostic trouble code. A false detonation signal will not cause ECM to set a code.
2. If a scan tester is available, connect it to the ALDL connector. 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-ECM 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/roadmaster/viii-1991-1996/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-v8__engine-sensors-switches) .

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

1. An open or short circuit on the KS wire to the ECM will cause a loss of the 12-volt KS controller signal. This will cause the ECM to fully retard ignition timing.
2. If a scan tester is available, connect it to the ALDL connector. 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 a DVOM to the ECM 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 ECM 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/roadmaster/viii-1991-1996/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-v8__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.

Electric AIR Control By-Pass Valve (5.0L & 5.7L VIN 7)

With engine at idle, check for at least 10 in. Hg to valve. Run engine at part throttle (less than 2000 RPM). Air should go into exhaust ports until system goes into closed loop, then divert the air to atmosphere. If this does not occur, check terminal harness connector to valve, check for short to ground in air solenoid harness or replace defective valve. Regardless of open or closed loop operation, air should always divert to atmosphere on heavy deceleration.

Electric AIR Pump Relay (5.7L "F" Body)

1. Start engine. With engine operating in open loop, electric air pump should run and air should be coming out of electric air pump exhaust port.
2. If electric air pump is operating, allow engine to idle for at least 3 minutes. With vehicle in closed loop (or about 3 minutes after start), ECM should de-energize electric air pump relay and electric air pump should stop. If this does not occur, go to step 3). If air pump operates as described, relay is functioning properly.
3. Remove air pump relay from underhood electrical center. Air pump should stop. If air pump stops, go to step 4). If air pump does not stop, check circuit to air pump for a short to battery voltage.
4. Connect ohmmeter between relay terminals E1 (Brown wire) and E4 (Red wire). Connect ground to relay terminal E2 (Brown wire). Apply battery voltage to relay terminal E5 (Brown wire). Continuity should exist between terminals E1 and E4 of relay ONLY with relay energized. If relay does not test as indicated, replace relay.

Electric AIR Pump Relay (5.7L "Y" Body)

Connect ohmmeter between relay terminals "A" (Black/Orange wire) and "E" (Red wire). Apply battery voltage to relay terminals "D" (Pink/Black wire) and "F" (Brown wire). Continuity should exist between terminals "A" and "E" of relay ONLY with relay energized. If relay does not test as indicated, replace relay.

AIR By-Pass Valve Solenoid (5.7L "Y" Body)

1. When engine is cold or during cold starts, ECM completes the ground circuit, energizing the by-pass solenoid and AIR pump. Air is directed to exhaust ports whenever engine is started.
2. When system goes into closed loop, ECM opens the ground circuit, de-energizing the by-pass solenoid and AIR pump. Air is then directed away from exhaust ports until air pump stops running.
3. To verify by-pass solenoid circuit or faulty by-pass solenoid, turn ignition off. Disconnect air by-pass solenoid connector. Turn ignition on. Using a test light connected to ground, probe air by-pass solenoid harness terminal "A" (Pink/Blue wire). If test light illuminates, go to next step. If test light does not illuminate, check for open ignition feed circuit.
4. Connect test light between air by-pass solenoid harness connector terminals "A" and "B". If test light illuminates, check for grounded air by-pass solenoid driver circuit No. 429 (Black/Pink wire) or a faulty ECM. If test light does not illuminate, go to next step.
5. Using Tech 1 scan tester, activate AIR system. With test light still connected to by-pass solenoid harness connector terminals "A" and "B", observe test light. If test light illuminated, check for faulty by-pass solenoid connection or a faulty air by-pass solenoid. If test light did not illuminate, check for faulty ECM connection, an open or shorted air by-pass solenoid driver circuit, or a faulty ECM.

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, and digital 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 ECM-controlled solenoid, verify vacuum is available to solenoid at 2000 RPM and check solenoid using appropriate procedure. See appropriate EGR CONTROL SOLENOID procedure below.

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.

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 ECM-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.

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.

FUEL EVAPORATION CONTROL (C-3)

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

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.

Damper Door - Wax Pellet Actuator Check (TBI)

1. Remove air cleaner assembly from vehicle. Allow air cleaner assembly to cool to less than 40°F (4°C). Damper door should be closed to outside (cold) air.
2. Reinstall air cleaner assembly. Start engine and observe damper door. As air cleaner assembly warms up, wax pellet should expand, closing off hot air delivery and opening cold air delivery.
3. If door does not respond as indicated, ensure door is not binding and calibrated damper spring is installed properly.

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 the correct coolant temperature without setting a diagnostic trouble code (Code 14 or 15). This could result in turning on the hot light without having an overheating condition. It could also result in engine overheating without turning on the hot light. 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 ECM provides a ground for the circuit. If circuit grounds between light and ECM, 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 ECM hot light driver terminal with a test light to battery voltage. Turn ignition on. If test light does not illuminate, ECM terminal connection is bad or ECM is faulty. If test light illuminates, turn ignition off. Disconnect ECM connectors. Jumper ECM hot light driver harness terminal to ground. Turn ignition on. If hot light does not illuminate, check for open circuit between hot light and ECM. If all circuits are intact 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 ECM connector. Probe ECM hot light driver harness terminal with a test light to battery voltage. If test light is off, replace ECM. If test light is on, repair short to ground in hot light driver circuit. If no short is present, replace instrument cluster.

Converter Clutch Solenoid

Disconnect harness connector to Torque Converter Clutch (TCC) solenoid. Measure resistance between TCC solenoid terminals "A" and "D". Solenoid resistance should be greater than 20 ohms. (Scheme 44)- (Scheme 49).

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 44)- (Scheme 49).

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 ECM. If harness is okay, see CONVERTER LOCK-UP SIGNAL FROM ECM below.

Converter Lock-Up Signal From ECM

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 the ALDL connector. (Scheme 44)- (Scheme 49). Accelerate vehicle to 45 MPH and note test light. If test light does not illuminate, problem is a faulty ECM connector or ECM.

Note. In the following schematics, Assembly Line Data Link (ALDL) connector is also referred to by manufacturer as Data Link Connector (DLC).

Scheme 43

Scheme 44

Scheme 45

Scheme 46

Scheme 47

Scheme 48

1-4 Shift System Check (Man. Trans. Corvette)

1. With engine off, depress clutch and place transmission in 1st gear. Shift transmission into 2nd or 3rd gear. If transmission cannot be shifted into 2nd or 3rd gear, check for short to voltage on circuit between 1-4 shift relay and 1-4 shift solenoid, defective 1-4 shift solenoid or internal mechanical transmission problem. (Scheme 50)
2. Turn ignition on with engine not running. Ground ALDL test terminal "B". (Scheme 43) Attempt to shift transmission into 2nd or 3rd gear. If transmission cannot be shifted into 2nd or 3rd gear, system is functioning correctly.
3. If transmission can be shifted into 2nd and 3rd gear, turn ignition off. Disconnect 1-4 shift relay connector. Turn ignition on and check for voltage from ground to harness terminals "D" and "E". If voltage is not present on both harness terminals, check for blown fuses or open circuit to terminal which did not illuminate test light.
4. If test light illuminated when touched to both terminals, ground ALDL test terminal "B" and connect test light from battery voltage to terminal "F" of 1-4 shift relay harness connector.
5. If test light does not illuminate, check for open in circuit No. 108 between relay and ECM, poor ECM terminal contact or defective ECM. If test light does illuminate, perform 1-4 SHIFT RELAY test procedures below.

SHIFT LIGHT CIRCUIT IDENTIFICATION

Scheme 49

1-4 Shift Light (Man. Trans. Corvette)

1. This testing procedure assumes that a problem exists with the 1-4 shift light. Use this procedure only if the light will not illuminate or illuminates all of the time.
2. Turn ignition on, with engine off. Note shift light. If shift light comes on, go to next step. If shift light does not come on, go to step 4).
3. Turn ignition off. Disconnect ECM connector "A". Turn ignition on. Note shift light. If shift light comes on, repair short to ground in circuit No. 776 (White wire). (Scheme 50) If shift light is off, replace ECM.
4. Ground ALDL test terminals "A" and "B". (Scheme 43) Note shift light. If shift light comes on, shift light circuit is okay, and no further testing is required. If shift light does not come on, go to next step.
5. Turn ignition off. Disconnect ECM connector "A". Turn ignition on. Jumper circuit No. 776 (White wire) to ground. (Scheme 50) Note shift light. If shift light does not come on, check for open in circuits No. 439 (Pink/Black wire) and No. 776 (White wire) or for faulty shift light bulb. If shift light comes on, check for faulty ECM connection or faulty ECM.

1-4 Shift Relay (Man. Trans. Corvette)

1. Turn ignition off. Disconnect 1-4 shift relay connector. Check for continuity between terminals "D" and "F" of relay. (Scheme 51) If continuity does not exist, replace relay. If continuity does exist, check for continuity between relay terminals "C" and "A". Continuity should also exist when relay is not energized. If continuity does not exist, replace relay.
2. Energize relay by applying battery voltage to terminal "D" of relay and grounding terminal "F". Check continuity between terminals "A" and "E". (Scheme 51) Continuity should exist while relay is energized. Replace relay if it does not test as described.

Scheme 50

1. Ensure diagnostic trouble Code 24 is not present. If Code 24 is present, diagnose Code 24 first. See appropriate TESTS W/CODES article in this section.
2. Turn ignition off. Raise and support vehicle. Disconnect reverse lock-out solenoid harness connector. Turn ignition on. Using a test light connected to ground, probe reverse lock-out solenoid terminal "B" (Brown wire). If test light illuminates, go to next step. If test light does not illuminate, check for an open circuit to terminal "B". see scheme 17
3. Connect test light to battery positive terminal. Probe reverse lock-out solenoid terminal "A" (Light Green wire). see scheme 17 If test light illuminates, check for faulty solenoid connection or faulty reverse lock-out solenoid. If test light does not illuminate, check for an open circuit to terminal "A", a faulty ECM connection or a faulty ECM.

Scheme 51

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

Note. For additional information on electric cooling fans, see appropriate ENGINE COOLING FANS article in the 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. See appropriate mini-schematic in «DIAGNOSTIC CHARTS»(/buick/roadmaster/viii-1991-1996/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-v8__diagnostic-charts) . 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 ECM. See appropriate mini-schematic in «DIAGNOSTIC CHARTS»(/buick/roadmaster/viii-1991-1996/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-v8__diagnostic-charts) . Disconnect coolant temperature sensor. This should set a code, causing ECM 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 ALDL with the ignition on and engine off will cause the ECM 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 ECM connector or ECM. Clear diagnostic trouble code(s) from ECM memory after testing.
3. If cooling fan functions normally during testing but fails to operate under normal conditions, check ECM 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. See appropriate mini-schematic in «DIAGNOSTIC CHARTS»(/buick/roadmaster/viii-1991-1996/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-v8__diagnostic-charts) . 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 appropriate TESTS W/CODES article in this section.

DIAGNOSTIC CHARTS

Note. In the following diagnostic tests, schematics, illustrations and flow charts are courtesy of General Motors Corp.

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

CHART C-10 - A/C CLUTCH CONTROL CKT (1 OF 2) (5.0L (VIN E) & 5.7L (VIN 7) "B" BODY)

The A/C clutch control relay is ECM controlled to delay A/C clutch engagement about .4 second after A/C is turned on. This allows ECM time to adjust engine RPM before A/C clutch engages. The ECM also disengages the A/C clutch during WOT operation.

When A/C selector switch is turned on, ignition voltage is applied to the pressure cycling switch. If A/C charge is sufficient, pressure switch will close to complete the circuit to the ECM and A/C clutch relay. When an A/C request signal is received by ECM, ECM will ground relay circuit No. 459 long enough to adjust idle RPM. Once idle RPM has been adjusted, ECM will remove ground from circuit No. 459, allowing voltage to be applied to A/C compressor clutch.

Note. Test numbers refer to test numbers on diagnostic charts. Tests indicating C-60 apply to manual A/C systems, and tests indicating C-68 apply to automatic A/C systems.

1. Checks to see if ECM is controlling A/C clutch relay.
2. Checks if clutch relay feed circuits are shorted to voltage.
3. Confirms 12 volt supply to A/C clutch relay.
4. Perform thorough A/C system diagnosis before replacing any A/C control components.

Diagnostic Aids

If climate control Code 09 is present, perform A/C system diagnosis. ECM will disengage A/C clutch whenever a power steering load or WOT operation is detected.

Chart C-10 Schematic (5.0L VIN E & 5.7L VIN 7 - "B" Body) A/C Clutch Control Circuit Diagnosis. Scheme 52

Chart C-10 Flow Chart (1 Of 2)(5.0L VIN E & 5.7L VIN 7 - "B" Body) A/C Clutch Control Circuit Diagnosis. Scheme 53

CHART C-10 - A/C CLUTCH CONTROL CKT (2 OF 2)(5.0L (VIN E) & 5.7L (VIN 7) "B" BODY)

Note. Test numbers refer to test numbers on diagnostic charts. Tests indicating C-60 apply to manual A/C systems, and tests indicating C-68 apply to automatic A/C systems.

1. Confirms 12 volt supply to A/C control relay. The A/C control relay is located in convenience center.
2. Jumpering harness connector will determine if the high pressure cut-off switch is open.

Chart C-10 Flow Chart (2 Of 2)(5.0L VIN E & 5.7L VIN 7 - "B" Body) A/C Clutch Control Circuit Diagnosis. Scheme 54

CHART C-10 - A/C CLUTCH CONTROL CKT (5.7L (VIN 7) "D" BODY)

When A/C selector switch is turned on, ignition voltage is applied to the pressure cycling switch. If A/C charge is sufficient, the pressure switch will close to complete the circuit to the ECM and A/C clutch relay. When A/C request signal is received by ECM, ECM will ground relay circuit No. 459 long enough to adjust idle RPM. Once idle RPM has been adjusted, ECM will remove ground from circuit No. 459, allowing voltage to be applied to the A/C compressor clutch. The ECM will also disable A/C clutch relay during WOT position.

Note. Test numbers refer to test numbers on diagnostic charts.

1. Checks for open A/C fuse.
2. Checks if ECM is controlling A/C clutch control relay.
3. Checks for grounded circuit No. 459 to ECM.

Chart C-10 Schematic (5.7L VIN 7 - "D" Body) A/C Clutch Control Circuit Diagnosis. Scheme 55

Chart C-10 Flow Chart (5.7L VIN 7 - "D" Body) A/C Clutch Control Circuit Diagnosis. Scheme 56

CHART C-12 - COOLING FAN CKT (5.7L (VIN P) "F" BODY)

This system uses 2 cooling fans. Cooling fans are controlled by ECM based on various inputs. Battery voltage is supplied to primary fan relay terminals D1 and F4 of secondary fan relay. Ignition voltage is supplied to terminal D5 of primary cooling fan relay and terminal F2 of secondary fan relay.

Grounding circuit No. 335 (relay terminal D2) energizes primary cooling fan relay, supplying battery voltage to primary cooling fan motor. Grounding circuit No. 473 (relay terminal F5) energizes secondary cooling fan relay, supplying voltage to secondary cooling fan motor.

ECM enables cooling fans when related diagnostic trouble code(s) are set.

Note. Test numbers refer to test numbers on diagnostic charts.

1. With diagnostic test terminal grounded, cooling fan control driver(s) will close, energizing cooling fan control relay(s).
2. Cooling fans should come on anytime A/C system is operating.
3. Comparing Tech 1 scan tester pressure and manifold gauge set pressure will determine if A/C refrigerant pressure sensor is out of calibration. An out of calibration A/C refrigerant pressure sensor can cause cooling fans to operate at wrong times.

If an overheating condition is suspected, verify if it is due to an actual boilover. If gauge or light indicates an overheat condition and boilover is not evident, inspect gauge circuit for malfunction.

If vehicle is overheating and gauge or light indicates so but cooling fan is not coming on, check coolant sensor temperature using a Tech 1 scan tester. Sensor may have shifted out of calibration and should be replaced. If engine is overheating and cooling fan is on, check cooling system.

Chart C-12 Schematic (5.7L VIN P - "F" Body) Cooling Fan Circuit Diagnosis. Scheme 57

Chart C-12 Flow Chart (1 Of 2)(5.7L VIN P - "F" Body) Cooling Fan Circuit Diagnosis. Scheme 58

Chart C-12 Flow Chart (2 Of 2)(5.7L VIN P - "F" Body) Cooling Fan Circuit Diagnosis. Scheme 59

CHART C-10 - A/C CLUTCH CONTROL CKT (1 OF 3)(5.7L (VIN P) "F" BODY)

The A/C clutch control relay is ECM controlled to delay A/C clutch engagement after A/C is turned on. This allows ECM to adjust engine RPM before A/C clutch engages.

ECM engages A/C clutch anytime A/C has been requested unless any of following conditions exist

1. High coolant temperature.
2. Low evaporator temperature.
3. Low battery voltage.
4. High engine RPM.
5. High A/C system pressure.
6. Low A/C system pressure.

Whenever A/C control assembly is placed in A/C mode, a 12-volt signal is sent to ECM. When ECM receives this signal, it will ground circuit No. 459, energizing A/C relay. An A/C refrigerant pressure sensor is used to monitor A/C pressure. If A/C pressure is greater than 414 psi (29.1 kg/cm 2 ) or lower than 38 psi (2.7 kg/cm 2 ), A/C clutch will not engage.

Code 66 will set if refrigerant pressure sensor signal wire becomes open, shorted to ground, or shorted to voltage. Code 67 will set if A/C clutch engages and no pressure change is detected.

ECM also monitors A/C evaporator temperature to cycle A/C clutch. If A/C evaporator temperature is out of range (high or low), ECM will disable A/C clutch relay. Code 71 will set if A/C evaporator temperature sensor circuits become open, shorted to ground, or shorted to voltage.

When ECM detects an A/C request, ECM will ground A/C clutch control relay driver circuit, closing relay contacts and allowing current to flow through relay to A/C compressor clutch. Cooling fans will also be turned on, unless vehicle speed is too high.

Note. Test numbers refer to test numbers on diagnostic charts.

1. Checks ECM's ability to control A/C clutch control relay.
2. Checks for grounded circuit No. 459 to ECM.
3. Before replacing control head, perform thorough A/C system diagnosis.

Before using CHART C-10, ensure ECM does not have any related diagnostic trouble code(s) stored. ECM will not activate A/C clutch with a stored diagnostic trouble code.

Chart C-10 Schematic (5.7L VIN P - "F" Body) A/C Clutch Control Circuit Diagnosis. Scheme 60

Chart C-10 Flow Chart (1 Of 3)(5.7L VIN P - "F" Body) A/C Clutch Control Circuit Diagnosis. Scheme 61

Chart C-10 Flow Chart (2 Of 3)(5.7L VIN P - "F" Body) A/C Clutch Control Circuit Diagnosis. Scheme 62

CHART C-10 - A/C CLUTCH CONTROL CKT (3 OF 3)(5.7L (VIN P) "F" BODY)

Note. Test numbers refer to test numbers on diagnostic charts.

1. If 5-volt reference signal is not present at A/C evaporator temperature sensor, A/C evaporator temperature would be at a fixed value. This would cause the A/C clutch to be engaged at all times when A/C is requested.

Chart C-10 Flow Chart (3 Of 3)(5.7L VIN P - "F" Body) A/C Clutch Control Circuit Diagnosis. Scheme 63

CHART C-12 - COOLING FAN CKT (5.7L (VIN P) "Y" BODY)

ECM controls cooling fans based on various inputs. Battery voltage is supplied to fan relays on terminal "E" and ignition voltage to terminal "D". Grounding circuit No. 335 (relay terminal "F") will energize primary cooling fan relay (fan No. 1) and supply battery voltage to primary cooling fan motor. Grounding circuit No. 473 (relay terminal "F") will energize secondary cooling fan relay (fan No. 2) and supply battery voltage to secondary cooling fan motor.

If any ECM codes are set or ECM is operating in fuel back-up mode, ECM will turn on both fans.

Note. Test numbers refer to test numbers on diagnostic charts.

1. With diagnostic test terminal grounded, cooling fan control driver(s) will close, which should energize fan control relays.
2. Cooling fans should come on anytime A/C system is operating.
3. Comparing Tech 1 scan tester pressure and manifold gauge set pressure will determine if A/C pressure sensor is out of range. An out-of-range A/C pressure sensor can cause cooling fans to operate at wrong times.

If an overheating condition is suspected, verify if it is due to an actual boilover. If gauge or light indicates an overheat condition and boilover is not evident, inspect gauge circuit for malfunction.

If vehicle is overheating and gauge or light indicates so but cooling fans are not coming on, check coolant sensor temperature using Tech 1 scan tester. Sensor may have shifted out of calibration and should be replaced. If engine is overheating and cooling fans are on, check cooling system.

Chart C-12 Schematic (5.7L VIN P - "Y" Body) Cooling Fan Circuit Diagnosis. Scheme 64

Chart C-12 Flow Chart (1 Of 2)(5.7L VIN P - "Y" Body) Cooling Fan Circuit Diagnosis. Scheme 65

Chart C-12 Flow Chart (2 Of 2)(5.7L VIN P - "Y" Body) Cooling Fan Circuit Diagnosis. Scheme 66

CHART C-10 - A/C CLUTCH CONTROL CKT (5.7L (VIN P) "Y" BODY)

A/C clutch relay is ECM controlled to delay A/C clutch engagement after A/C is turned on. This allows ECM to adjust engine RPM before A/C clutch engages. ECM will engage A/C clutch anytime A/C has been requested unless any of following conditions exist

1. High coolant temperature.
2. Wide Open Throttle (WOT).
3. High oil temperature.
4. High A/C system pressure.
5. High engine RPM.

ECM can determine A/C request by sending a voltage signal to A/C control head. When A/C control switch is closed, A/C request voltage signal is grounded. This is shown on Tech 1 scan tester as A/C request YES.

When a request for A/C has been detected by ECM, ECM grounds A/C clutch control relay drive circuit, closing relay contacts and energizing compressor clutch portion of circuit. If system is properly charged, circuit will be complete to A/C compressor clutch. When A/C request has been detected by ECM, cooling fans will be turned on unless vehicle speed is too high.

Note. Test numbers refer to test numbers on diagnostic charts.

1. Checks ECM's ability to control A/C clutch relay.
2. Checks for grounded circuit No. 459 to ECM.
3. Before replacing A/C control components, ensure a basic A/C system problem is not present.

ECM will not activate A/C clutch if ECM diagnostic trouble codes are stored. If necessary, see appropriate TESTS W/CODES article in this section.

Chart C-10 Schematic (5.7L VIN P - "Y" Body) A/C Clutch Control Circuit Diagnosis. Scheme 67

Chart C-10 Flow Chart (1 Of 2)(5.7L VIN P - "Y" Body) A/C Clutch Control Circuit Diagnosis. Scheme 68

Chart C-10 Flow Chart (2 Of 2)(5.7L VIN P - "Y" Body) A/C Clutch Control Circuit Diagnosis. Scheme 69

Scheme 70

Scheme 71

Scheme 72

Scheme 73

Scheme 74

See also:
• MISCELLANEOUS CONTROLS
• HALL EFFECT CAMSHAFT SENSOR
• CTS RESISTANCE VALUES
• INTAKE AIR TEMPERATURE (IAT) SENSOR
• ENGINE SENSORS & SWITCHES
• DIAGNOSTIC CHARTS