Engine Controls - System/component Tests Oldsmobile Toronado Trofeo

INTRODUCTION

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

Note. Testing individual components does not isolate possible shorts or opens in the control harness of electronically controlled systems. Use an ohmmeter and appropriate wiring diagram in WIRING DIAGRAMS to isolate shorts or opens in harness. All voltage tests should be performed with a Digital Volt-Ohmmeter (DVOM) with a minimum 10-megohm input impedance, unless stated otherwise in testing procedures.

WASTEGATE/BOOST PRESSURE TEST

1. Inspect wastegate and actuator assembly for linkage damage. Check condition of hose from throttle body to wastegate solenoid and from wastegate solenoid to actuator. Remove hose.
2. Connect a hand-held Vacuum/Pressure Pump (J-23738) in series with component Gauge (J-28474) to actuator assembly hose.
3. With 4 psi (.28 kg/cm 2 ) pressure applied, actuator should move rod .015" (.38 mm). Replace actuator if not operating properly. Check new unit and crimp threads on rod to maintain proper calibration. Remove test equipment. Reconnect actuator-to-wastegate solenoid hose.

WASTEGATE ACTUATOR

1. Disconnect vacuum hose to wastegate actuator. Apply vacuum to actuator. If wastegate actuator moves, replace wastegate control valve solenoid.
2. If wastegate actuator does not move, check vacuum hose. Replace vacuum hose if defective. If vacuum hose is okay, disconnect actuator linkage at wastegate. Apply vacuum to actuator. If actuator moves, wastegate is sticking. If actuator does not move, replace actuator.

WASTEGATE SOLENOID

Disconnect wastegate solenoid connector and vacuum hose. Apply 12-volt power source to solenoid. Using a hand-held vacuum pump, apply vacuum to solenoid. A clicking noise should be heard from wastegate solenoid and vacuum should flow through valve. If these conditions are not met, solenoid is defective.

Scheme 36

Scheme 37

A/C ON SWITCH SYSTEM TEST

1. Turn ignition switch to RUN position. Move mode selector switch to OFF position. With A/C control assembly connector connected, measure voltage between mode selector switch Brown wire and ground. For wiring schematics, see mini-schematics in A/C CLUTCH under MISCELLANEOUS ECM CONTROLS in this article.
2. Battery voltage should be present. If battery voltage is present, mode selector switch is operating normally. If battery voltage is not present, check Brown wire from selector switch to fuse for an open circuit.
3. Check voltage between mode selector Brown/White wire and ground. Voltage should not be present. If voltage was present, replace mode selector switch.

A/C PRESSURE SENSOR (2.3L & 3.1L J BODY)

A malfunction in A/C pressure sensor circuit will set a related trouble code. For testing procedures, see appropriate TESTS W/CODES article in this section. For wiring schematics, see mini-schematics in A/C CLUTCH under MISCELLANEOUS ECM CONTROLS in this article.

A/C PRESSURE SWITCH

1. Connect A/C pressure gauges to system and start engine. Note 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 freon delivery system.
2. Using an ohmmeter, check continuity between pressure switch terminals. Continuity should be present on both high and low switches (if equipped with both). If continuity is not present, check switch terminal connectors. If terminal connectors are okay, replace A/C pressure switch. For wiring schematics, see mini-schematics in A/C CLUTCH under MISCELLANEOUS ECM CONTROLS in this article.

BRAKE SWITCH

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

CAMSHAFT SENSOR (3.8L VIN C)

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

COOLANT LEVEL SENSOR/COOLANT LEVEL LIGHT

1. Ensure radiator coolant level is full and Codes 14, 26 and 32 are not set. Correct as necessary. Turn ignition on and note coolant level light. It should be on as a bulb check. If not, go to step 2). Start engine and note coolant level light. It should be off. If light stays on and coolant level is not low, check for a short in the bulb ground circuit. If short is not present, connect a test light to battery voltage and touch ECM coolant level light driver terminal. If test light illuminates, go to step 4).
2. Disconnect ECM connector containing coolant level light driver terminal. Turn ignition on. Using a jumper wire, ground ECM coolant level light driver terminal. If light does not illuminate, check for an open in the coolant level light circuit, including a bad bulb. If light does illuminate, ECM driver is faulty.
3. Disconnect coolant level sensor harness connector (located on right side of radiator), coolant light should come on again. If it does, no problem is present. If light does NOT come on again, check for terminal "B" circuit of sensor shorted to ground.
4. Disconnect sensor wiring harness connector. Connect jumper wire between harness side terminal "B" to ground. If coolant light does not go out, go to step 5). If coolant light does go out, check circuit between wiring harness side terminals "A" and "C" to ECM. If circuit is okay, replace defective coolant level sensor.
5. Using a voltmeter, check for 5 volts at harness side terminals "B" and "C". (Scheme 38) If 5 volts is not available, check for open circuit, faulty ECM connection or faulty ECM. If both terminals read 5 volts, disconnect ECM connector. Check sensor terminal "B" and "C" circuits for short to voltage or each other. If circuits are okay, ECM is faulty.

Scheme 38

COOLANT TEMPERATURE SENSOR (CTS)

If a coolant sensor related code is present, see appropriate TESTS W/CODES article. An out-of-calibration sensor may not set a 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 up. See CTS RESISTANCE VALUES table.

CTS RESISTANCE VALUES

CRANKSHAFT POSITION SENSOR (2.3L IDI)

Disconnect crankshaft sensor connector, located above oil filter. Set ohmmeter to 2K position, measure resistance across sensor terminals. Resistance should be between 500-900 ohms. Set voltmeter on the 2-volt AC scale. Crank engine and measure voltage across sensor terminals. Voltmeter reading should be .1 volt or greater. If resistance reading is not as specified or sensor does not produce a voltage reading, replace faulty crank sensor. Also, check if sensor is still magnetized. Replace as necessary.

CRANKSHAFT POSITION SENSOR (DIS)

Disconnect crankshaft sensor harness connector. Set ohmmeter to 2K position, measure resistance across sensor terminals. Resistance should be 900-1200 ohms. Set voltmeter on the 2-volt AC scale. Crank engine and measure voltage across sensor terminals. See the Voltmeter reading should be .1 volt or greater. If resistance reading is not as specified or sensor does not produce a voltage reading, repair faulty wiring or crank sensor.

Note. The following table contains information updated as per Technical Service Bulletin Numbers 89-6E-28 (Buick) and 90-168-6E (Chevrolet).

NORMAL CRANK SENSOR VOLTAGE OUTPUT RANGE (3.1L VIN "T")

DUAL CRANK (COMBINATION) SENSOR (3.3L C(3)I SYSTEM)

This test should only be performed if vehicle will not start, injectors will not pulse and spark plugs will not fire. This simulates a dual crank sensor signal. If spark and injector pulse occur, dual crank sensor or sensor connections are bad.

1. Turn ignition off. Disconnect No. 6 spark plug wire from coil tower. Install Spark Tester (ST-125) to coil tower. Install spark plug wire to spark tester.
2. Connect injector test light to any injector connector. Connect jumper wire across dual crank sensor connector terminals "A" and "B". (Scheme 39)and (Scheme 40). Turn ignition on, engine off (DO NOT crank engine).
3. Using a test light connected to ground, momentarily touch dual crank sensor terminal "A". Note injector test light and spark tester. Test light should blink and spark should be present at spark tester. NOTE: Repeatedly grounding terminal "A" at dual crank sensor or terminals "C" and "B" at C(3)I module may cause engine to flooded.
4. If spark was present and test light came on, check for poor connection at dual crank sensor terminal. If connections are okay, replace faulty dual crank sensor. If spark and test light did not come on, check for poor connection at C(3)I module or replace faulty C(3)I module.

Scheme 39

Scheme 40

EGR POSITION SENSOR

See EMISSION SYSTEMS & SUB-SYSTEMS in this article.

ENGINE OIL TEMPERATURE SENSOR (5.7L VIN 8)

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 table. Also see CODE 52 and CODE 62 in 3.1L, 5.0L & 5.7L TROUBLE CODE CHARTS.

ENGINE OIL TEMPERATURE SENSOR RESISTANCE

KNOCK SENSOR

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 voltmeter 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 in this article and appropriate TESTS W/CODES article.

CAMSHAFT SENSOR/HALL EFFECT SWITCH (CADILLAC EXCEPT BROUGHAM)

1. Turn ignition off. Disconnect 6-terminal, 5-wire connector at HEI distributor. Connect a DVOM to terminal "E" (pos.) and terminal "D" (neg.) on distributor side of connector. (Scheme 41)
2. Turn ignition on and note DVOM reading. Using ignition key, bump starter to rotate distributor. Note DVOM reading. Repeat procedure several times. DVOM should read either zero or 12 volts. Voltmeter should NOT read a steady voltage.
3. Crank engine and note voltage reading. Depending on voltmeter, reading may fluctuate between zero and 12 volts or average about 6 volts. If voltmeter readings are correct, Hall Effect switch is okay.
4. If voltmeter readings are not correct, turn ignition off and remove distributor. Reconnect 3-terminal connector and connect voltmeter to 6-terminal, 5-wire connector as previously described. Turn ignition on and rotate distributor by hand. Replace Hall Effect switch if voltage remains either high or low.

Scheme 41

MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR

A malfunction in the MAP sensor circuit should set a related code in ECM memory. If a code is present, see appropriate TESTS W/CODES article. An out-of-calibration sensor may not set a 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. If driveability condition improves, replace MAP sensor.

1. With ignition on and engine off, check MAP sensor parameter using a "Scan" tester connected to the ALDL connector. Voltage should be as specified in MAP SENSOR VOLTAGE RANGE table. If MAP sensor voltage is as specified, go to step 2). 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.
2. Using a hand-held vacuum pump, apply 10 in. Hg to MAP sensor and note voltage change. Voltage should drop to about 1.2-2.3 volts or 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 42

MAP SENSOR VOLTAGE RANGE

MANIFOLD AIR TEMPERATURE (MAT) SENSOR

If a MAT sensor related code is present, see appropriate TESTS W/CODES article. An out-of-calibration sensor may not set a trouble code. Use following procedure to test calibration. Disconnect MAT sensor harness connector. Connect ohmmeter between sensor terminals. Sensor resistance should be as specified. See MAT SENSOR RESISTANCE table. With vehicle sitting overnight, MAT sensor and coolant sensor should have close to the same resistance reading.

MAT SENSOR RESISTANCE

MASS AIRFLOW SENSOR

A malfunction in the MAF sensor circuit will result in the setting of a related trouble code. For testing procedures, see appropriate code(s) in appropriate TESTS W/CODES article.

OXYGEN SENSOR (O2)

1. Start engine and warm to operating temperature. Disconnect oxygen sensor. Connect a DVOM between Purple lead of oxygen sensor and ground. Place meter 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 Purple wire from the ECM and the 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 Purple wire from the ECM. Hold jumper in one hand and touch positive post of battery with other hand to cause oxygen sensor to produce less than .3 volts. For additional testing procedures, see appropriate TESTS W/CODES article.

P/N SWITCH

Disconnect P/N switch (located on transmission) harness connector. Connect ohmmeter between the P/N switch terminals. (Scheme 43) Continuity should be present only when gear shift selector is in Park or Neutral. If continuity is not present, check P/N switch adjustment or replace defective P/N switch.

Scheme 43

POWER STEERING PRESSURE SWITCH (PSPS)

Disconnect P/S pressure switch harness connector. Connect ohmmeter between P/S pressure switch terminals. Start engine. With no-load on power steering, continuity should not be present. Turn steering wheel to full stop, continuity should now be present. If readings are not as specified, replace defective P/S pressure switch.

PRESSURE/BARO SENSOR CARBURETED 5.0L (VIN Y)

1. Connect jumper harness between sensor and sensor harness to enable checking voltage with DVOM with circuit intact. With ignition on, engine off, check voltage between pressure sensor terminals "A" and "B". (Scheme 44) Voltage should be as specified. See PRESSURE SENSOR VOLTAGE RANGE table. If okay, go to next step. If voltage is not as specified, check vacuum hose. If vacuum hose is okay, replace pressure sensor.
2. Using a hand-held vacuum pump, apply 10 in. Hg to pressure sensor and note voltage change. Voltage should drop to about 1.2-2.3 volts or less from specified sensor voltage range on table. If voltage is not as specified or if voltage reading does not immediately follow vacuum change, pressure sensor is faulty.

Note. "Scan" tester will not read same voltage as voltmeter since ECM inverts voltage signal internally.

Scheme 44

PRESSURE SENSOR VOLTAGE RANGE

THROTTLE POSITION SENSOR (TPS)

Install jumper wires to enable connection of a DVOM in parallel between TPS harness connectors. Connect DVOM positive lead to Blue wire terminal. Connect negative lead to Black wire terminal. (Scheme 45) Turn ignition on, 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 TPS. See the appropriate ADJUSTMENTS article.

A malfunction in the TPS circuit should set a related trouble code. For further information, see appropriate TESTS W/CODES article. Also see TPS adjustment procedure in the appropriate ADJUSTMENTS article in this section.

Scheme 45

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

A/C RELAYS

See MISCELLANEOUS ECM CONTROLS in this article.

FUEL PUMP RELAY

1. Disconnect fuel pump relay. See SYSTEM & COMPONENT TESTING article. Apply battery voltage and ground to fuel pump relay winding terminals. To identify fuel pump relay terminals, see appropriate wiring diagram in WIRING DIAGRAMS.
2. Using an ohmmeter, check continuity between fuel pump relay power and fuel pump relay drive terminals. Continuity should exist. If continuity does not exist, fuel pump relay is defective.
3. To by-pass fuel pump relay on-vehicle (fuel pump not operating), turn ignition off. Disconnect fuel pump relay connector. Using a fused jumper wire, connect fuel pump test connector to positive side of battery. Fuel pump should run.
4. If fuel pump runs, check for faulty connections to relay or replace defective relay. To locate fuel pump test connector, see the SYSTEM & COMPONENT TESTING article in this section.

Scheme 46

SOLENOIDS

Note. All ECM controlled solenoids should have at least 20 ohms of resistance.

CANISTER PURGE SOLENOID

See Canister Purge Solenoid tests in the Fuel Evaporation Control Section..

MIXTURE CONTROL SOLENOID

See FUEL SYSTEM in this article and CODE 23 in 5.0L CARBURETED TROUBLE CODES in appropriate TESTS W/CODES article.

ILC/RVB/EGR SOLENOID

1. Disconnect solenoid harness connector. Install vacuum pump to manifold vacuum 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. Solenoid should energize. With solenoid energized, apply vacuum to solenoid. Vacuum should not pass through solenoid. If results are not as specified, replace defective solenoid.

See AIR INDUCTION SYSTEMS in this article.

IDLE AIR CONTROL (IAC) MOTOR

See IDLE CONTROL SYSTEM in this article.

IDLE SPEED CONTROL (ISC) MOTOR

See IDLE CONTROL SYSTEM in this article.

FUEL SYSTEM

Note. For fuel system pressure testing, see BASIC DIAGNOSTIC PROCEDURES article.

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. Repair as necessary. Reconnect vacuum hose to pressure regulator and note fuel pressure on gauge. Compare first and second reading. 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 unsatisfactory, 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 for 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.

See RELAYS, SOLENOIDS, MOTORS & MODULES in this article.

FUEL PUMP RELAY BY-PASS PROCEDURE

If fuel pump will not energize, relay may be by-passed to test fuel pump. Turn ignition off. Using a fused jumper wire, apply battery voltage to fuel pump test connector (located in engine compartment). Fuel pump should turn on. For fuel pump test connector location, refer to SYSTEM & COMPONENT TESTING article.

FUEL CONTROL (CARBURETED)

Note. For testing of feedback system, including oxygen sensor, mixture control solenoid, ECM and related wiring, refer to SYSTEM PERFORMANCE CHECK in BASIC TESTING article.

FLOAT LEVEL (ON-VEHICLE)

1. Warm engine to normal operating temperature. With engine at idle and choke wide open, insert Float Level Gauge (J-34935-1 or BT-8420-A) into carburetor air horn vent slot. Allow gauge to float freely.
2. Observe that mark on gauge lines up with top of air horn casting. Setting should be within 2/32" of specified float level setting. See FLOAT LEVEL SPECIFICATIONS table. If float level is not as specified, remove air horn and adjust float level.

FLOAT LEVEL SPECIFICATIONS

HOT AIR CHOKE

1. Warm engine to normal operating temperature. Check choke valve. Choke valve should be fully open. If choke is not fully opened, touch choke housing and hot air inlet pipe or hose to determine if sufficient heat is reaching choke thermostatic spring.
2. If choke housing or hot air inlet pipe is not getting hot, check choke housing, choke heat pipe or manifold choke heat stove for restricted passages. Repair or replace components.

Disconnect mixture control solenoid harness connector. Check resistance between solenoid terminals. Normal resistance is 20-32 ohms. Check for unwanted shorts to ground between solenoid connector terminals and solenoid body. Resistance to ground should be infinite. If resistance is less than 10 ohms or if solenoid has continuity to ground, replace solenoid.

OXYGEN SENSOR

See ENGINE SENSORS & SWITCHES in this article.

VACUUM BREAK

Plug air bleed hole (if equipped) on vacuum break. Using a hand-held vacuum pump, apply 15 in. Hg to vacuum break. Check and see if plunger has moved through its full travel. Observe vacuum gauge. Vacuum should hold for at least 20 seconds. If plunger did not move to its full travel or vacuum did not hold as specified, replace vacuum break.

FUEL INJECTOR(S)

Disconnect fuel injector harness connector. Measure resistance across injector terminals. Resistance should be as specified. See FUEL INJECTOR RESISTANCE table.

FUEL INJECTOR RESISTANCE

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

INJECTOR BALANCE TEST

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. 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 H - TESTING W/O CODES article.

See ENGINE SENSORS & SWITCHES in this article.

1. Disconnect harness connector to motor. Check resistance across IAC coil terminals "A" to "B" and "C" to "D". Resistance should be 40-80 ohms. (Scheme 47) If okay, 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. Testing Idle Air Control (IAC) motor requires a "Scan" tester capable of cycling ECM output devices. Flow charts in the TESTS W/CODES articles may refer to the Tech 1 tester, General Motors' version of this tester.

Scheme 47

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

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

IDLE SWITCH (CADILLAC EXCEPT BROUGHAM)

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.

Disconnect ISC connector. Connect an ohmmeter across Pink and Black/White wire terminals ("A" and "B") of ISC motor connector. (Scheme 48) With throttle closed, continuity should exist. With throttle open enough to relieve tension from the ISC plunger, continuity should not exist.

Scheme 48

IDLE LOAD COMPENSATOR (ILC)

1. With engine running and transmission in Park, hold throttle lever part way open and allow ILC plunger to fully extend. Apply finger pressure to ILC plunger. Using a hand-held vacuum pump/gauge, apply 20 in. Hg to ILC plunger.
2. Plunger should begin to retract. If not, replace ILC plunger. If plunger retracts, observe vacuum gauge. Vacuum should hold for at least 20 seconds. If vacuum does not hold, replace ILC plunger.

CHART C-4-1 (C3I MISFIRE AT IDLE 3.3L VIN N)

1. If engine misfires under load only, see C-4-2 below. With engine idling at normal operating temperature, disconnect IAC. While observing engine RPM, temporarily disconnect each injector connector. All injector(s) should result in a drop in RPM. If it does, see ROUGH, UNSTABLE OR INCORRECT IDLE in TESTS W/O CODES article If it doesn't, turn ignition OFF, and install injector tester J 34730-2 or equivalent on injector connector which did not result in an RPM drop. Crank engine while observing injector test light. Light should blink. If it doesn't, see NO START (PFI W/C3I). If it does, then proceed to next step.
2. With ignition OFF, install spark tester (ST-125) J 26792 or equivalent on plug lead(s) which did not result in drop in RPM (1,3,5 at plug and 2,4,6 at coil). Spark should jump tester gap while cranking engine. If it does, check for faulty, worn or cracked spark plug(s), plug fouling due to engine mechanical fault. If spark plugs are OK, then see CUTS OUT MISSES in TESTS W/O CODES article. If it doesn't, then check resistance of plug wire which did not fire spark tester. Wire resistance should be less than 30,000 ohms each and wires shouldn't be grounded. Are wires are OK. If Not, then replace faulty wire(s) and retest. If OK go to next step.
3. Remove coil from module. Inspect coils, plug wire and plug wire nipples. They should be free of carbon tracking. If NOT, replace faulty component. If OK got to next step.
4. Check secondary coil resistance. It should be 5-8K Ohms resistance for 3.3 VIN N models and 10-13 Ohms resistance for 3.8L VIN C models. If NOT, replace coil. If YES, then go to next step.
5. Install a known good coil. Spark should jump tester gap at problem cylinder with engine idling. If it did not, then there is a faulty C(3)1 module. If it did, then original ignition coil is faulty.

Chart C-4-1 Schematic, Misfire At Idle (3.3L VIN N). Scheme 49

Chart C-4-1 Schematic, Misfire At Idle (3.8L VIN C). Scheme 50

CHART C-4-2 (C3I MISFIRE UNDER LOAD IDLE 3.3L VIN N)

1. If engine misfires at idle, see C-4-1 above. With engine idling at normal operating temperature, disconnect IAC. While observing engine RPM, temporarily disconnect each injector connector. All injector(s) should result in a drop in RPM. If it does, check for faulty, worn or cracked spark plug(s), plug fouling due to engine mechanical fault. If spark plugs are OK, then see CUTS OUT MISSES in TESTS W/O CODES article. If it doesn't, turn ignition OFF, and install injector tester J 3470-2 or equivalent on injector connector which did not result in an RPM drop. Crank engine while observing injector test light. Light should blink. If it doesn't, see NO START (PFI W/C3I). If it does, then proceed to next step.
2. With ignition OFF, install spark tester (ST-125) J 26792 or equivalent on plug lead(s) which did not result in drop in RPM (1,3,5 at plug and 2,4,6 at coil). Spark should jump tester gap while cranking engine. If it does, check for faulty, worn or cracked spark plug(s), plug fouling due to engine mechanical fault. If spark plugs are OK, then see CUTS OUT MISSES in TESTS W/O CODES article. If it doesn't, then check resistance of plug wire which did not fire spark tester. Wire resistance should be less than 30,000 ohms and shouldn't be grounded. Are wires are OK? If Not, then replace faulty wire(s). If OK go to next step.
3. Remove coil from module. Inspect coils, plug wires and plug wire nipples. They should be free of carbon tracking. If NOT, replace faulty component. If YES , then check secondary coil resistance. It should be 5-8K Ohms resistance for 3.3 VIN N models and 10-13 Ohms resistance for 3.8L VIN C models. If NOT, replace coil. If YES, then go to next step.
4. Install a known good coil. Spark should jump tester gap at problem cylinder with engine idling. If it did not, then there is a faulty C3I module. If it did, then original ignition coil is faulty.

IGNITION SYSTEM (EXC. C3I)

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

ELECTRONIC SPARK TIMING (EST) ADVANCE SYSTEM

1. A malfunction in the EST circuit should set a related 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. A noticeable change in engine speed should occur. If no change occurs, see DIAGNOSTIC CIRCUIT CHECK in «BASIC TESTING»(/oldsmobile/toronado-trofeo/1990-1990/remont/testing-diagnostics/#engine-controls-basic-testing) article.

ELECTRONIC SPARK CONTROL (ESC) RETARD SYSTEM (WITHOUT ESC CONTROLLER)

1. An open or short circuit on the ESC wire to the ECM will set a related 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 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 in ENGINE SENSORS & SWITCHES in this article.

ELECTRONIC SPARK CONTROL (ESC) RETARD SYSTEM (WITH ESC CONTROLLER)

1. An open or short circuit on the ESC wire to the ECM will cause a loss of the 12-volt ESC 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 controller signal. On vehicles equipped with automatic transmission, it may be necessary to place transmission in Drive for timing change to occur. Also, see KNOCK SENSOR in ENGINE SENSORS & SWITCHES in this article.

AIR PUMP

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 back. Replace valve if airflow is allowed against the direction of flow.

DECELERATION VALVE

1. Remove air cleaner. Remove and plug vacuum hose to air cleaner. Connect tachometer to engine. With engine at idle, remove deceleration valve signal hose from vacuum port.
2. Reconnect signal hose to deceleration valve while listening for air flow through ventilation pipe into deceleration valve. Engine speed should drop when hose is reconnected.
3. If airflow lasts less than one second or engine speed does not drop, check for defective hose(s) or deceleration valve.

ELECTRIC DIVERT & ELECTRIC SWITCHING VALVE (EDES)

With engine at idle, check for at least 10 in. Hg to EDES. 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 not, check terminal harness connector to EDES or replace defective EDES.

PRESSURE OPERATED ELEC. DIVERT/ELEC. SWITCHING (PEDES)

1. When engine is cold, port solenoid should be energized, allowing airflow to exhaust ports.
2. When engine is warming up, port switch should be de-energized (off) and converter solenoid should be energized, forcing airflow past the converter valve to the catalytic converter.
3. On the divert mode, both solenoids are de-energized, which opens the converter valve, allowing air out to divert/relief tube to atmosphere. If valves are not operating as specified, check circuit to solenoids. Repair or replace components as necessary.

EARLY FUEL EVAPORATION (EFE) CARBURETED 5.0L (VIN Y)

Note. Before performing EFE testing, allow engine to cool until coolant temperature is less than 105°F (41°C).

EARLY FUEL EVAPORATION SYSTEM CHECK

1. Locate and note position of EFE actuator arm. On some models, actuator arm may be protected by metal cover, which must be removed and then replaced after service has been performed.
2. When engine is cold, valve should close as actuator link pulls into diaphragm housing. If valve closes, go to step 6). If not, stop engine and remove vacuum hose to EFE valve. Restart engine and check for vacuum at hose. If vacuum is present, go to step 4).
3. If vacuum is not present, check vacuum supply to Thermal Vacuum Switch (TVS), located in coolant passage of intake manifold. Repair as necessary. If vacuum is present at TVS and coolant temperature is less than 105°F (40°C), replace TVS. CAUTION: Exhaust manifold will become very hot once engine is started. Wear heavy gloves when handling exhaust system components.
4. Attempt to move actuator arm by hand. If valve opens freely, vacuum motor diaphragm is defective. Replace EFE valve and actuator motor.
5. If lever will not move freely, try to free valve using Manifold Valve Lubricant (1050422). Allow time for lubricant to penetrate. If valve cannot be freed, replace valve and actuator motor.
6. If valve closes in step 2), allow engine to warm. When coolant temperature exceeds 105°F (40°C), valve should open. If valve does not open, stop engine, remove vacuum hose from EFE valve. Restart engine. If vacuum is present at vacuum hose and coolant temperature is greater than 105°F (40°C), replace TVS.

EXHAUST GAS RECIRCULATION (EGR)

Note. Some vehicles may use integral EGR/ILC/RVB, TCC/EGR, or EGR/CP solenoid valves.

There are 5 types of EGR systems used: backpressure (positive and negative), digital, electronic and pulse width modulated systems.

SYSTEM TEST

Start and run engine to normal operating temperature. With engine at idle, RPM should drop as EGR valve is opened by pushing up on underside of EGR diaphragm.

EGR CONTROL SOLENOID

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. Solenoid should have at least 20 ohms of resistance.

DIGITAL EGR VALVE

1. Start and allow engine to idle. With engine at normal operating temperature, disconnect digital EGR valve solenoid harness connector. Using a 12-volt power source, very quickly energize EGR solenoid No. 1. RPM should drop slightly. (Scheme 51)
2. Next, energize EGR solenoid No. 2. RPM should drop slightly more than step 1). If RPM drops, EGR is okay. If not, check for plugged EGR passages or defective digital EGR valve. Check EGR solenoid resistance. See DIGITAL EGR SOLENOID RESISTANCE table.

For additional testing procedures, see appropriate TESTS W/CODES article.

DIGITAL EGR SOLENOID RESISTANCE (1)

Scheme 51

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. On carbureted engines, place fast idle cam on high step. 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 not be by-passed.
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 and pausing through hose.
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 not, replace EGR valve.

PULSE WIDTH MODULATED EGR VALVE

1. Place transmission in Park or Neutral. With engine at idle and at normal operating temperature, push up on EGR valve diaphragm. Engine RPM should drop. If engine RPM did not drop, clean EGR valve and passages.
2. Check EGR valve movement with engine RPM change from 2000 RPM to idle. If EGR valve moves with RPM change, check Park/Neutral switch adjustment or open circuit. If EGR valve did not move, ground ALDL test connector. If EGR valve moves now, EGR valve is functioning properly. If not, go to next step.
3. Turn engine off and disconnect EGR solenoid connector. Connect 12-volt test light between EGR solenoid connector terminals. Turn ignition on and ground ALDL test connector. Test light should flash repeatedly.
4. If test light flashes, check vacuum to EGR solenoid at 2000-3000 RPM. If engine does not use a vacuum regulator, at least 7 in. Hg should be present at solenoid. If engine is equipped with a vacuum regulator, 2-10 in. Hg should be present.
5. If vacuum is greater than 10 in. Hg, replace regulator. If vacuum is less than 2 in. Hg, vacuum at solenoid is okay. Check EGR solenoid connections and/or faulty EGR solenoid.

INTEGRATED ELECTRONIC EGR VALVE

1. Turn ignition off. Connect vacuum pump to EGR valve. Apply vacuum and observe EGR valve. EGR valve should not move. If it does, check vent filter for restriction. Replace EGR valve if necessary.
2. Turn ignition on and repeat step 1). When applying vacuum, EGR valve should not move. If EGR moves, a fault code should be present. See appropriate TESTS W/CODES article.

FUEL EVAPORATION CONTROL

Note. Two types of canister control valves are used on General Motors vehicles. One is fixed to canister (Type 1) and the other is removable (Type 2).

CANISTER CONTROL VALVE (TYPE 1)

1. Note vacuum hose location and disconnect hoses from control valve and canister. Install a short vacuum hose to lower tube of carbon canister valve. Blow into hose. Air should not pass through canister. If it does, replace valve/canister.
2. Using a hand-held vacuum pump, apply 15 in. Hg to trigger port. With vacuum applied, again blow into hose installed on bowl vent tube. Air should now flow through canister. If not, replace valve/canister.

CANISTER CONTROL VALVE (TYPE 2)

1. Note vacuum hose location and remove valve from vehicle. Install a short length of hose to vacuum trigger port. Blow into hose. Air should not pass through. If it does, diaphragm is ruptured and valve must be replaced.
2. Using a hand-held vacuum pump, apply 15 in. Hg to vacuum trigger port. Vacuum should hold for 20 seconds. If not, replace valve.
3. With vacuum still applied to trigger port, blow through canister tube. Air should exit from vacuum purge tube. If not, replace valve.

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.

EVAP PURGE VALVE SOLENOID

1. Disconnect purge valve solenoid harness connector and vacuum hose. Apply 10 in. Hg to ported 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 purge valve solenoid. Vacuum should release. If not, replace purge valve solenoid. Solenoid resistance should be at least 20 ohms.

FUEL TANK PRESSURE CONTROL VALVE

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

THERMAL BOWL VENT VALVE (TBVV) CARBURETED 5.0L (VIN Y)

1. Remove thermal bowl vent valve. Allow valve to cool to less than 90°F (32°C). Install a short hose to either valve port. Lightly blow into hose. No air should pass through valve. If it does, replace TBVV.
2. Warm valve to greater than 120°F (49°C). Once again, blow into hose. Air should now pass through valve. If not, replace TBVV.

CHECKING PCV VALVE FUNCTION

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 PCV leaking valve or hose could cause

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

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

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, 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 insure 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 at regular intervals (at least every 30,000 miles). Check all hoses and clamps for failure or deterioration.

TEMPERATURE SENSOR

1. Air cleaner temperature should be less than 86°F (30°C). Place thermometer as close to sensor inside air cleaner. Start and idle engine. Damper door should close off outside air immediately.
2. When damper door starts to open snorkel passage, remove air cleaner cover and read thermometer temperature. Thermometer should read 131°F (55°C).
3. If damper door does not open to outside air at the specified temperature, replace defective thermostatic air cleaner temperature sensor.

VACUUM DIAPHRAGM MOTOR

1. Turn engine off. Disconnect vacuum hose to vacuum motor. Apply 7 in. Hg to vacuum motor. Damper door should close. If not, check if linkage is properly hooked up.
2. With vacuum still applied, trap vacuum in vacuum diaphragm motor by bending hose. Damper door should remain closed. If damper door does not remain closed, replace vacuum diaphragm motor assembly.

MISCELLANEOUS ECM CONTROLS

Note. Although not considered true engine performance-related systems, some controlled devices may affect driveability if they malfunction.

A/C Clutch Relay

1. Disconnect A/C clutch relay harness connector. Using proper mini-schematic and an ohmmeter, check continuity between A/C clutch relay winding terminals. Continuity should exist. Check continuity between clutch drive circuit terminals of relay. Continuity should not exist. (Scheme 52)-38.
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.

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A/C WOT CUT-OUT RELAY

1. Disconnect WOT cut-out relay harness connector. Using an ohmmeter, check continuity between relay terminals "A" and "C" and "B" and "E". Continuity should be present on these circuits.
2. Using jumper wires, apply battery voltage to relay terminal "C" and ground to relay terminal "A". Continuity should not exist between relay terminals "B" and "E" while relay is energized. If continuity is not as specified, replace defective WOT cut-out relay.

Scheme 72

Scheme 73

COOLING FAN

Note. For additional information on electric cooling fans, see ELECTRIC COOLING FANS article in ENGINE COOLING.

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. (Scheme 74)-62. 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 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. (Scheme 74)-62. 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.

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COOLANT LEVEL LIGHT

See COOLANT LEVEL SENSOR & COOLANT LEVEL LIGHT in ENGINE SENSORS & SWITCHES in this article.

HOT LIGHT OR COOLANT TEMPERATURE LIGHT

1. Turn ignition on and note indicator light. Light should be on as a bulb check. If light is not on, go to step 2). Start engine. Light should go off. If light stays on and engine temperature is low, scan coolant temperature sensor reading. If reading indicates a false high reading, see COOLANT TEMPERATURE SENSOR in this article. If reading is low, check for a short in the bulb ground circuit. If short is not present, connect a test light to battery voltage and touch ECM temperature light driver terminal. If test light illuminates, ECM is faulty.
2. Disconnect ECM connector containing temperature light driver terminal. Turn ignition on. Using a jumper wire, ground ECM temperature light driver terminal. If light does not illuminate, check for an open in the temperature light circuit, including a bad bulb. If light does illuminate, ECM driver is faulty.

CONVERTER CLUTCH SOLENOID

Disconnect harness connector to TCC solenoid. Measure resistance between TCC solenoid terminals "A" and "D". 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 96)-86.

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.

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. (Scheme 96)-86. Accelerate vehicle to 45 MPH and note test light. If test light does not illuminate, problem is a faulty ECM connector or ECM. On some models, lock-up signal may be checked at ALDL terminal "F" instead of at ECM terminal.

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SHIFT LIGHT (MANUAL TRANSMISSION)

1. These tests assume a shift light problem exists. 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. Shift light should not be on. If light is on, check for a short to ground between the bulb and the ECM, or a bad ECM.
3. With ignition on and engine off, ground "test" terminal of ALDL connector. SERVICE ENGINE SOON light should start to flash and shift light should come on. If light comes on, go to next step. If SERVICE ENGINE SOON light does not flash, perform DIAGNOSTIC CIRCUIT CHECK as described in «BASIC TESTING»(/oldsmobile/toronado-trofeo/1990-1990/remont/testing-diagnostics/#engine-controls-basic-testing) article.
4. If shift light does not come on, ground Tan/Black wire at ECM terminal B7 (A12 on Corvette or GF4 on 2.3L Beretta, Cutlass Calais & Grand Am) using a jumper wire. If light still does not come on, check for blown GAUGES fuse (AIRBAG fuse on Corvette), blown bulb or open circuit between fuse and ECM. If light came on when grounding terminal B7 (or A12 or GF4) with a jumper wire, problem is a bad ECM connection or bad ECM.

Scheme 120

Scheme 121

1-4 SHIFT SYSTEM CHECK (MANUAL TRANSMISSION 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 No. 138 between 1-4 shift relay and 1-4 shift solenoid, defective 1-4 shift solenoid, or internal mechanical transmission problem. (Scheme 123)
2. Turn ignition on with engine not running. Ground ALDL "test" terminal "B". 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 terminal, 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 did illuminate, perform 1-4 SHIFT RELAY test procedures.

1-4 SHIFT LIGHT (MANUAL TRANSMISSION CORVETTE)

1. This testing procedures 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. Shift light should not be on. If light is on, check for a short to ground between the bulb and the ECM, or a bad ECM.
3. With ignition on and engine off, ground "test" terminal "B" of ALDL connector. SERVICE ENGINE SOON light should start to flash and 1-4 shift light should come on. If light comes on, go to next step. If SERVICE ENGINE SOON light does not flash, perform DIAGNOSTIC CIRCUIT CHECK as described in «BASIC TESTING»(/oldsmobile/toronado-trofeo/1990-1990/remont/testing-diagnostics/#engine-controls-basic-testing) article.
4. If 1-4 shift light does not come on, ground ECM terminal C13 using a jumper wire. If light still does not come on, check for blown GAUGES fuse, blown bulb or open circuit between fuse and ECM. If light came on when grounding terminal C13 with a jumper wire, problem is a bad ECM connection or bad ECM.

Scheme 122

1-4 SHIFT RELAY (MANUAL TRANSMISSION CORVETTE)

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

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See also:
• BASIC TESTING