Engine Controls - Basic Testing Chevrolet Lumina I

INTRODUCTION

The following diagnostic steps will help prevent overlooking a simple problem. This is also where to begin diagnosis for a no-start condition.

The first step in diagnosing any driveability problem is verifying the customer's complaint with a test drive under the conditions during which the problem reportedly occurred.

Before entering self-diagnostics, perform a careful and complete visual inspection. Most engine control problems result from mechanical breakdowns, poor electrical connections or damaged/misrouted vacuum hoses. Before condemning the computerized system, perform each test listed in this article.

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 (GENERAL HELP INFORMATION) article in the ENGINE PERFORMANCE section.

GENERAL MOTORS A & C CHART REFERENCE

Note. Perform all voltage tests with a Digital Volt-Ohmmeter (DVOM) with a minimum 10-megohm input impedance, unless stated otherwise in test procedure.

VISUAL INSPECTION

Visually inspect all electrical wiring, looking for chafed, stretched, cut or pinched wiring. Ensure electrical connectors fit tightly and are not corroded. Ensure vacuum hoses are properly routed and not pinched or cut. See VACUUM DIAGRAMS article in the ENGINE PERFORMANCE section to verify routing and connections (if necessary). Inspect air induction system for possible vacuum leaks.

Compression

Check engine mechanical condition with a compression gauge, vacuum gauge, or an engine analyzer. See engine analyzer manual for specific instructions. For compression specifications, see C - SERVICE & ADJUSTMENT SPECIFICATIONS article in the ENGINE PERFORMANCE section.

Exhaust System Backpressure

Before replacing any components, check exhaust system for restrictions. The exhaust system can be checked with a vacuum gauge or a low pressure (0-5 psi) pressure gauge.

If a vacuum gauge is used, connect vacuum gauge hose to intake manifold vacuum port and start engine. Observe vacuum gauge. Open throttle part way and hold steady. If vacuum gauge reading slowly drops after stabilizing, exhaust system should be checked for a restriction. If using a low pressure gauge, connect gauge in one of the following manners

1. Check At AIR Pipe

Remove rubber hose at exhaust manifold AIR pipe check valve and remove check valve. Install pressure gauge to hose and nipple via Propane Enrichment Device(J-26911). Nipple should be inserted into exhaust manifold AIR pipe.

1. Check At Oxygen Sensor

Remove oxygen sensor. Install backpressure tester in place of oxygen sensor. After test is completed, coat oxygen sensor threads with anti-seize compound.

Diagnosis

1. Start engine and bring to operating temperature. Increase engine speed to 2000-2500 RPM and note gauge. Reading should not exceed 1.25 psi (.09 kg/cm 2 ). Exhaust system is restricted if specification is exceeded.
2. Check exhaust system for collapsed pipe, heat distress and possible internal muffler failure. If none of these conditions exist, check for restricted catalytic converter. Replace as required.

PCM REPLACEMENT CHECK

Many test procedures and test charts in ENGINE PERFORMANCE lead to conclusion that PCM is faulty. Before replacing PCM, check driven circuits and PCM Quad-Drivers (QDR) using following procedures and accompanying flow chart. See QDR Check Flow Chart below.

1. Using a DVOM, backprobe PCM drive circuit in question and measure pin voltage with ignition on. If system voltage is present, go to next step. If system voltage is not present, turn ignition off. Disconnect PCM connector. Measure voltage on connector terminal for suspect circuit. If low voltage is measured, check circuit for an open or short to ground. Repair as necessary. If system voltage is measured, PCM is defective.
2. With DVOM still backprobing PCM at suspect circuit, ground DLC "test" terminal. Monitor voltage drop on circuit for at least 2 minutes. Voltage drop should not be greater than .5 volt. Some circuits may have low voltage until DLC "test" terminal is grounded. A "switching" operation should occur. Some Torque Converter Clutch (TCC) systems have pressure switches in series with TCC solenoid. On these applications, complete this circuit by disconnecting transmission/transaxle connector and using a test light in series between terminals "A" and "D" of transmission/transaxle connector.
3. If voltage drops and then floats back up, this occurs when QDR circuit is going into current limiting. Check circuit current flow (.75 amp maximum, except as noted in QDR check chart). See QDR Check Flow Chart below.

Note. For PCM-equipped vehicles, transmission/transaxle functions can only be energized through use of TECH 1 scan tester. Shift solenoids on these models will not energize when DLC is grounded.

QDR Check Flow Chart. Scheme 152

NO START DIAGNOSIS (A-3)

Note. Some vehicles are equipped with anti-theft systems (VATS or PASS-Key(R)) which will not allow vehicle to be started if improper starting procedures or improperly coded ignition keys are used. Both fuel injection and cranking systems will be disabled. Loss of fuel enable signal from anti-theft decoder module should set a trouble code in PCM memory.

DEFINITION

No start is defined as engine cranks properly, but does not start. Engine may fire a few times.

NO START - ENGINE CRANKS OKAY (3.1L & 3.4L WITH DIS)

Note. Check battery, engine cranking speed and fuel supply before performing the following tests.

General Inspection

1. Ensure proper starting procedure is being used.
2. Visually check vacuum hoses for splits, kinks and proper connections, as shown on Vehicle Emission Control Information label. Check ignition wires for cracking, hardness and proper connections at both coil pack and spark plugs.
3. In very cold temperatures, check oil is proper viscosity and not contaminated with gasoline.

Ignition System (3.1L)

1. Disconnect tachometer wire (if equipped). A shorted tachometer or tachometer circuit will prevent vehicle from starting.
2. Install scan tester. Check for stored PCM trouble codes. Scan TP sensor voltage. If TP sensor reading is greater than 2.5 volts, use diagnostic trouble Code 21 chart first. See appropriate TESTS W/CODES article in the ENGINE PERFORMANCE section.
3. Scan RPM while cranking engine. If RPM is displayed on scan tester, go to step 7). If RPM is not displayed, check for spark on 2 wires (2-4 or 4-6) using Spark Tester (ST-125). Check one wire at a time. Leave other wires connected to spark plugs while cranking.
4. If spark occurs on both wires, go to next step. If no spark occurs on either wire, use diagnostic trouble Code 82. See appropriate TESTS W/CODES article in the ENGINE PERFORMANCE section. If spark occurs on one wire only, go to step 6).
5. Turn ignition off. Disconnect 6-wire ignition module connector. Turn ignition on. Monitor scanned RPM while momentarily touching RPM reference circuit wire (circuit No. 430) of ignition module harness connector with a test light connected to battery voltage. (Scheme 153) If RPM is indicated on scan tester, problem is faulty ignition module-to-harness connection or faulty ignition control module. If RPM is not indicated, problem is open or short to ground in RPM reference circuit or faulty PCM.
6. If spark occurs on one wire only, check pair of wires for plug that did not spark. Each wire should measure less than 30,000 ohms resistance. If wires are okay, switch coil assemblies. If problem moves with coil, replace faulty coil. If problem does not follow coil, ignition control module is faulty.
7. Scan fuel pump signal (PPSW) during cranking. If voltage is not indicated, see appropriate diagnostic trouble Code 54 chart. If voltage is indicated, turn ignition off. Install fuel pressure gauge. Turn ignition on. Fuel pressure should be 41-47 psi (2.9-3.3 kg/cm 2 ).
8. If fuel pressure is not as specified, diagnose fuel system. If fuel pressure is okay, disconnect injector No. 1 or 6 harness connector. Turn ignition on, engine off. Using a test light connected to ground, probe test light on injector harness circuit No. 839 (Pink wire). (Scheme 153)
9. If test light does not illuminate, check for open in circuit No. 839 (Pink wire). If test light illuminates, disconnect 10-pin injector harness connector. Install DVOM and set to 1 k/ohm position. Connect DVOM positive probe to injector harness terminal "D" (Pink wire) and touch DVOM negative probe to injector harness terminals "A", "B", "C", "F" and "G". Resistance should be less than 20 ohms.
10. If resistance is not as specified, check injector harness circuit. If circuit is okay, replace faulty injector. If resistance is as specified, set DVOM to DC volts position. With DVOM positive probe connected to battery voltage, probe injector harness terminals "A", "B", "C", "H", "J" and "K" while cranking engine. DVOM should read/toggle from zero to 12 volts on each terminal.
11. If reading is as specified, problem is not present at this point. If reading is not as specified, check for open injector circuit, faulty PCM connections or faulty PCM.

Fuel System (3.1L)

Before checking fuel system for a no-start condition, check ignition for adequate spark. Check for proper fuel pump pressure and capacity. See BASIC FUEL SYSTEM CHECKS in this article and INJECTOR BALANCE/COIL TEST in I - SYSTEM & COMPONENT TESTING article in the ENGINE PERFORMANCE section.

Scheme 153

Fuel System (3.4L VIN X)

Before checking fuel system for a no-start condition, check ignition for adequate spark. Check for proper fuel pump pressure and capacity. See BASIC FUEL SYSTEM CHECKS in this article and INJECTOR BALANCE/COIL TEST in I - SYSTEM & COMPONENT TESTING article in the ENGINE PERFORMANCE section.

Scheme 154

NO START - ENGINE CRANKS OKAY (3.8L WITH C( 3 )I)

Note. Before performing following tests, check battery condition, engine cranking speed and for adequate fuel in tank.

1. Ensure proper starting procedure is being used. Visually check vacuum hoses for splits, kinks and proper connections, as shown on Vehicle Emission Control Information label. Check ignition wires for cracking, hardness and proper connections at both coil pack and spark plugs.
2. Remove spark plugs. Check and replace as necessary. In very cold temperatures, ensure oil is proper viscosity and not contaminated with gasoline.

Ignition System (VIN K, L & 1)

1. Ensure TP sensor scan is less than 2.5 volts. If not, see Code P0123 chart. Scan PASS-Key(R) II. Display should show ENABLED. If not, diagnose theft deterrent system. Check for stored trouble codes. See TESTS W/CODES article in the ENGINE PERFORMANCE section. If engine has not been started for at least 8 hours, MAT sensor scan temperature should be close to ECT sensor scan temperature.
2. Disconnect tachometer wire (if equipped). A shorted tachometer or tachometer circuit will not allow vehicle to start. Disconnect cam sensor and attempt to start engine. If engine starts, see Code P0341 chart. If engine does not start, go to next step.
3. Reconnect cam sensor connector. Compare scanned ECT sensor temperature with actual coolant temperature. If scanned value are not close, replace coolant sensor. Depress accelerator pedal about 25 percent throttle angle. Attempt to start engine. If engine does not start, go to next step. If engine starts, check IAC counts on scan tester. Check for blocked IAC passages.
4. Disconnect all injector connectors and install injector test light on each injector harness connector. All lights should be off and should blink as engine is cranked. If any injector lights are on, go to step 8). If lights do not blink at all while cranking, go to step 9). If all lights are off and blink as engine is cranked, go to next step.
5. Check for adequate spark using Spark Tester (ST-125). Check for spark on plug wires No. 1, 3 and 5 (one at a time). Leave matching plug wire connected while checking for spark. If spark jumped across tester on all plug wires, check for fouled spark plugs or for fuel system as cause of no start. Go to FUEL SYSTEM test or see BASIC FUEL SYSTEM CHECKS in this article. If spark did not jump tester or was not present on any plug wire, check poor ignition module connection or faulty ignition module.
6. If spark did not jump tester on all plug wires, ensure spark plug wire resistance is less than 30,000 ohms. Ensure ignition coil secondary resistance is 5000-6500 ohms at room temperature. Replace as necessary. If wires and coils are okay, remove coil that did not fire. Verify coil primary resistance of.5-.9 ohm. Replace coil if necessary. If coil is okay, connect test light across ignition module terminals of problem coil.
7. Crank engine. If test light flashes, check for poor coil-to-module connections. If connections are okay, replace faulty coil. If test light does not flash, replace ignition module.
8. Turn ignition off. Disconnect PCM Black connector. Turn ignition on. If all lights are off now, replace PCM. If any lights are still on, repair short to ground in that injector drive circuit.
9. Check ignition module power supply (F/P-IGN fuse and circuit). Repair as necessary. Disconnect fuel injector connector. Turn ignition on. With a test light connected to ground, check for battery voltage on Pink wire of injector harness. If test light is on, go to next step. If test light is off, check INJ fuse. If fuse is blown, repair short to ground and replace fuse. If fuse is okay, check power supply to fuse and circuit between fuse and the injector harness connector.
10. Turn ignition off. Disconnect ignition module connector. Turn ignition on. Install injector test light to any injector harness connector. Connect test light to battery voltage, and repeatedly touch terminal "D" of ignition module harness connector. (Scheme 155) Injector test light should flash each time test light is touched to terminal "D". If injector test light flashes, go to step 12).
11. If injector test light does not flash, check injector drive circuit between PCM and injector harness connector for open or short to voltage. Repair as necessary. If injector drive circuit is okay, check for open, short to ground or short to voltage on fuel control circuit No. 430 (Purple/White wire). If circuit is okay, problem is faulty connection at PCM fuel control terminal or faulty PCM.
12. Turn ignition off. Using proper jumper adapter from Adaptor Kit(J-35616), connect a fused jumper wire between ignition module harness connector terminal "N" and battery voltage. Connect a second jumper between ignition module harness connector terminals "M" and ground. Connect DVOM between ignition module harness connector terminal "H" and battery voltage. Observe voltmeter while cranking engine. Voltmeter should read about 1-3 volts.
13. If voltage is high, check circuit No. 646 for open or short to ground. If circuit No. 646 is okay, replace faulty crank sensor. If voltage is low, check circuit No. 646 for an open or short to voltage, circuit No. 645 for an open and circuit No. 644 for an open or short to ground. If all circuits are okay, replace faulty crank sensor.
14. If voltage is about 1-3 volts, move DVOM lead from terminal "H" to terminal "G". Crank engine and once again monitor voltage. Voltmeter should read about 5-7 volts. If voltage is correct, go to next step. If voltage is less than 5-7 volts, check for open or short to voltage in circuit No. 643. If voltage is greater than 5-7 volts, check for a short to ground on circuit No. 643. If no problem is found, crank sensor is faulty.
15. If voltage is close to 5-7 volts, turn ignition on. Probe ignition module harness connector terminals "P" with a DVOM connected to ground. If battery voltage is not present, repair open in ignition module power supply circuit. If battery voltage is present, problem is poor ignition module connections or faulty ignition module.

Fuel System (VIN L)

1. Before checking fuel system for a no-start condition, check ignition for adequate spark. Check for proper fuel pump pressure and capacity. See BASIC FUEL SYSTEM CHECKS.
2. Turn ignition off. Install fuel pressure gauge. Using a fused jumper wire connected to battery voltage, jumper fuel pump test terminal. Turn ignition on. Listen for fuel pump operation and note fuel pressure gauge reading.
3. If fuel pump operates and fuel pressure is okay, go to next step. If fuel pump does not operate, go to step 8). If fuel pump operates, but fuel pressure is not present, go to BASIC FUEL SYSTEM CHECKS.
4. Remove jumper wire. Remove fuel pump relay. Connect test light between fuel pump relay connector Orange wire and Black/White wire terminals. If test light illuminates, go to next step. If test light does not illuminate, connect test light between ground and relay connector Orange wire terminal. If test light illuminates, check for open in Black/White wire. If test light does not illuminate, check for open in Orange, Pink or Red wire.
5. Turn ignition off. Connect test light between relay connector Dark Green/White wire and Black/White wire. Turn ignition on. If test light illuminates for about 2 seconds, go to next step. If test light does not illuminate, check for poor relay connections. If connections are okay, replace fuel pump relay.
6. Turn ignition off. Connect test light to ground. Backprobe PCM connector Dark Green/White terminal (fuel pump driver circuit). Turn ignition on. If test light illuminates for about 2 seconds, check for open in Dark Green/White wire. If test light does not illuminate, go to next step.
7. Disconnect PCM connector. Using test light connected to battery voltage, probe PCM connector Dark Green/White wire terminal. If test light illuminates, check Dark Green/White wire for short to ground. If test light does not illuminate, check for faulty PCM connector or faulty PCM.
8. Turn ignition off. Remove fuel pump relay. Using a fused jumper wire, jumper relay connector Orange wire terminals. Turn ignition on. Fuel pressure gauge should indicate fuel pressure. If fuel pressure is present, check for poor relay connection, open in Red wire to fuel pump test terminal or faulty fuel pump relay. If fuel pressure is not present, go to next step.
9. Turn ignition off. Raise and support vehicle. Disconnect fuel pump connector at fuel pump. Connect test light between fuel pump connector terminals. Turn ignition on. If test light illuminates, replace fuel pump. If test light does not illuminate, check for open in Gray or Black wire fuel pump.

Scheme 155

BASIC FUEL SYSTEM CHECKS (A-7)

Fuel Pressure Relief

Fuel system is under pressure. Pressure must be relieved prior to servicing fuel system. Fuel pressure may be relieved by using one of the following methods.

1. On all models, disconnect fuel pump at rear body connector. Start engine and run engine until it stalls. Crank starter for 3 seconds to remove remaining fuel from fuel lines. Turn ignition off. Reconnect rear body connector.
2. Install Fuel Pressure Gauge (J-34730-1) on fuel pressure connector of fuel rail.

Fuel Pressure Check

1. Relieve fuel pressure as previously described in FUEL PRESSURE RELIEF. Connect Fuel Pressure Gauge (J-34730-1) to fuel pressure fitting on fuel rail. With gauge installed, turn ignition on. With ignition on and engine off, fuel pressure should read within specification. See FUEL PRESSURE table. If no fuel pressure is present, go to step 5).
2. Start engine. Pressure should drop 3-10 psi (.2-.7 kg/cm 2 ). Turn ignition off. Pressure should hold. If pressure does not hold, check for leaking injectors or fittings. If injectors or fittings are not leaking, replace pressure regulator.
3. If pressure is present but less than specification, check for restricted delivery line or fuel filter. Repair as necessary. If no restriction is evident, apply battery voltage to fuel pump test connector using a 10-amp fused jumper wire. For location of fuel pump test connector, see COMPONENT LOCATIONS in appropriate I - SYSTEM & COMPONENT TESTING article in the ENGINE PERFORMANCE section.
4. Gradually pinch off fuel return line between gauge and fuel tank. If fuel pressure increases to within specification, replace fuel pressure regulator. If fuel pressure does not increase with line pinched, check for faulty in-tank fuel pump or partially blocked fuel strainer.
5. Apply battery voltage to fuel pump test connector using a 10-amp fused jumper wire. For location of fuel pump test connector, see COMPONENT LOCATIONS in I - SYSTEM & COMPONENT TESTING article in the ENGINE PERFORMANCE section. Observe fuel pressure reading. If fuel pressure is still not present, check wiring between test connector and fuel pump. If wiring is okay, replace fuel pump.
6. If fuel pressure is present with voltage applied to test connector, test fuel pump relay and voltage supply to relay. See I - SYSTEM & COMPONENT TESTING article in the ENGINE PERFORMANCE section.

FUEL PRESSURE

Fuel Pump Relay

See MOTORS, RELAYS & SOLENOIDS in appropriate I - SYSTEM & COMPONENT TESTING article in the ENGINE PERFORMANCE section.

Fuel Pump Relay By-Pass Procedure

See FUEL DELIVERY in I - SYSTEM & COMPONENT TESTING article in the ENGINE PERFORMANCE section.

FIELD SERVICE MODE CHECK

Note. Field service mode check can only be performed on vehicles equipped with 12-pin DLC with a wire present in test terminal "B". See DATA LINK CONNECTOR (DLC) TEST TERMINALS table.

Note. Oxygen sensor may cool off while engine is idling. This causes system to go into "open loop". To restore "closed loop" mode, run engine at part throttle several minutes and accelerate from idle to part throttle several times.

Field service mode check confirms proper fuel system operation and verifies "closed loop" operation. Clear codes and perform this test after any repair is completed. When performing this check, always engage parking brake and block DRIVE wheels. Parking brake on FWD models does NOT hold drive wheels.

1. Start engine. With engine running, ground DLC terminal "B". (Scheme 156) In "closed loop" mode, Malfunction Indicator Light (MIL) will flash once a second.
2. In "open loop", MIL will flash 2.5 times a second. If MIL is off most of the time, a lean exhaust is indicated. If MIL is on most of the time, a rich exhaust is indicated.

DATA LINK CONNECTOR (DLC) TEST TERMINALS

Scheme 156

Scheme 157

HEI-EST DISTRIBUTOR

Note. The only adjustments that can be made to HEI/EST ignition system are basic ignition timing (on distributor-type ignitions) and spark plug gap.

Spark

1. If factory tachometer is connected at coil tachometer terminal, disconnect it before performing tests. When removing spark plug wire from spark plug, twist and pull on boot (not on wire).
2. Using Spark Tester (ST-125), check for spark at coil wire (if applicable) and at each spark plug wire using spark tester. Check spark plug wire resistance on suspect wires. Resistance should be less than 30,000 ohms.

Ignition Coil Power Source

1. Turn ignition on. Using voltmeter, check voltage between terminal "+" of ignition coil and ground on models with remote-mounted coil.
2. On models equipped with integral ignition coil, check voltage between BAT terminal and ground at distributor. Battery voltage should exist. If battery voltage does not exist, check for open circuit, blown ignition fuse or defective ignition switch.

Ignition Coil Resistance

1. Turn ignition off. Remove distributor cap and coil assembly. Invert cap. (Scheme 158) Set ohmmeter to low scale. Connect leads to coil BAT and TACH terminals. Resistance should be zero or nearly zero. If resistance is not zero or nearly zero ohms, replace ignition coil.
2. Set ohmmeter on high scale. Connect one lead to coil secondary terminal and other lead to ground terminal. If resistance reading is infinite, replace ignition coil.

Scheme 158

Distributor Pick-Up Coil Short & Resistance Checks

1. Disconnect pick-up coil leads from HEI/EST module terminals "N" and "P". Set ohmmeter to middle scale. Connect one ohmmeter lead to either pick-up coil lead and the other lead to distributor housing. Flex pick-up coil leads by hand to check for intermittent shorts to ground. Reading should be infinity at all times. If resistance is not infinite, replace pick-up coil.
2. Connect ohmmeter between both pick-up coil leads. Check for intermittent open circuit by flexing wires and connectors. Resistance should be 500-1500 ohms. If resistance is not as specified, replace pick-up coil.

Tach Pulse (RPM) Signal

1. Connect a scan tester to the DLC. RPM should be indicated on tester when engine is cranked or running. If scan tester is not available, tach pulse (RPM reference from ignition module) will be indicated as a voltage signal on a DVOM (with a minimum 10-megohm input impedance) when DVOM is touched to PCM terminal circuit No. 430 with engine cranking.
2. A tach pulse signal may be simulated (to test PCM response) by connecting a test light in series between battery and PCM terminal circuit No. 430. Each time test light is touched to and removed from circuit No. 430, PCM will see this as a tach signal. For circuit and terminal reference, see appropriate schematic under NO START - ENGINE CRANKS OKAY.

1. If factory tachometer is connected to coil tachometer terminal, disconnect tachometer before performing tests. When removing spark plug wire from spark plug, twist and pull on boot, NOT on wire.
2. Using Spark Tester (ST-125), check for spark at each spark plug wire using spark tester. Leave other wires connected while checking for spark. Check spark plug wire resistance on suspect wires. Resistance should be less than 30,000 ohms (12,000 ohms on 1.9L).

Turn ignition on. Check Pink/Black or Pink wire of ignition module for battery voltage. If battery voltage is not present, check ignition or PCM fuse. If fuse is not blown, check for open between fuse and ignition module.

If ignition coil is suspected of causing misfire or no-spark condition, switch coil locations on DIS module. If problem follows questionable coil, check ignition coil resistance or replace original coil. For ignition coil resistance, see IGNITION COIL RESISTANCE table.

IGNITION COIL RESISTANCE

Crankshaft Sensor Pick-Up Coil Short & Resistance Checks

1. Set DVOM on 2000-ohm scale position. Connect DVOM leads to crank angle sensor connector, located on side of engine block. Turn ignition off. Disconnect ignition module connectors. Measure resistance between crankshaft sensor terminals at ignition module connector.
2. Crankshaft sensor resistance should be within specification range listed in CRANKSHAFT SENSOR RESISTANCE table. If resistance is not as specified, replace sensor. If sensor is within specification, go to next step.
3. With sensor installed in block, connect one ohmmeter lead to either sensor terminal at ignition module. Touch other lead of ohmmeter to engine block. No continuity should exist. If continuity exists, sensor or harness is shorted to ground and must be repaired or replaced.

CRANKSHAFT SENSOR RESISTANCE

Crankshaft Sensor Output Signal

Set DVOM on 2-volt AC scale. Connect voltmeter leads to crankshaft sensor installed in side of engine block. Crank engine and observe voltmeter reading. Crank angle sensor should generate a voltage signal of about .05 volt at slow cranking speed to greater than .1 volt (100 mV) at high cranking speed. With engine running, voltage signal will be much greater.

Connect scan tester to DLC. RPM should be indicated on tester when engine is cranked or running. Tach pulse (RPM reference) will be indicated as a voltage signal when a DVOM (with a minimum 10-megohm input impedance) is used to backprobe RPM "high reference" circuit. For circuit and terminal reference, see appropriate schematic in NO START - ENGINE CRANKS OKAY.

Disconnect tachometer wire (if equipped). A shorted tachometer will prevent vehicle from starting. Disconnect cam sensor, and attempt to start engine. If engine starts, see appropriate cam sensor trouble code in TESTS W/CODES article in the ENGINE PERFORMANCE section. Check for adequate spark using Spark Tester (ST-125). Check for spark on plug wires No. 1, 3 and 5 (one at a time). Leave matching plug wire connected while checking for spark. When removing spark plug wire from spark plug, twist and pull on boot. DO NOT pull on wire.

Turn ignition on. Check for battery voltage on Pink/Black wire to ignition module. If battery voltage is not present, check for blown ignition fuse. If fuse is not blown, check for open between fuse and ignition module.

Disconnect ignition coil leads. Use an ohmmeter to check ignition coil resistance. Primary resistance should be .5-.9 ohm. Secondary resistance should be 5000-8000 ohms. Replace ignition coil if not within specification.

Tach Pulse (RPM Reference) Signal

Connect scan tester to DLC. RPM should be indicated on tester when engine is cranked or running. Tach pulse (RPM reference) will be indicated as a voltage signal when a DVOM (with a minimum 10-megohm input impedance) is used to backprobe circuit No. 430 PCM terminal. For circuit and terminal reference, see appropriate schematic in NO START - ENGINE CRANKS OKAY.

IDLE SPEED & IGNITION TIMING

Ensure idle speed and ignition timing are set to specification. For adjustment procedures, see appropriate D - ON-VEHICLE ADJUSTMENTS article in the ENGINE PERFORMANCE section.

DIAGNOSTIC CIRCUIT CHECK

The Diagnostic Circuit Check determines

1. If Malfunction Indicator Light (MIL) works.
2. If PCM is operating and can recognize a fault.
3. If any codes are stored.

After performing procedures in PRELIMINARY INSPECTION & ADJUSTMENTS, BASIC FUEL SYSTEM CHECKS and BASIC IGNITION SYSTEM CHECKS, this is the starting point for utilizing the self-diagnostic system for determining computer-related problems. (Scheme 159)and (Scheme 160). After performing necessary tests as described in the diagnostic circuit check, if no codes are indicated and driveability problems still exist, see H - TROUBLE SHOOTING - NO CODES article in the ENGINE PERFORMANCE section and SCAN TESTER USAGE in TESTS W/CODES article in the ENGINE PERFORMANCE section.

Note. On vehicles equipped with 16-pin DLC or 12-pin DLC without test terminal "B", use of Tech 1 scan tester is required to perform diagnostic circuit check. See DATA LINK CONNECTOR (DLC) TEST TERMINALS table.

1. Check operation of MIL. Turn ignition on with engine off. MIL should be on steady. If MIL illuminates and stays on steady, go to step 3). If MIL does not illuminate, go to A-1, MIL INOPERATIVE. If MIL flashes, go to step 4).
2. On vehicles equipped with 16-pin DLC or 12-pin DLC without test terminal "B", install Tech 1 scan tester and follow scan tester manufacturer's instructions to proceed with test. If MIL does not come on, go to A-1, MIL INOPERATIVE. If MIL comes on, check for diagnostic trouble codes and diagnose codes using TESTS W/CODES article in the ENGINE PERFORMANCE section. On vehicles equipped with 12-pin DLC with test terminal "B", go to next step.
3. Grounding DLC terminal "B" at this time should cause MIL to flash a Code 12, followed by any codes stored in PCM memory. (Scheme 156) MIL going from bright to dim is not considered a code. If MIL dims or remains on and does not flash Code 12, see A-2, MIL ON STEADY OR WON'T FLASH CODE 12. NOTE: On some models, as long as a 30-second pause may occur between code flashes. This is normal and does not indicate necessary component replacement.
4. If MIL begins to flash as soon as ignition is turned on, check for a short to ground on the diagnostic test terminal wire between DLC terminal "B" and PCM terminal No. 5. If circuit is okay, replace PCM.

Scheme 159

Scheme 160

A-1, MIL INOPERATIVE

1. If Malfunction Indicator Light (MIL) does not illuminate with ignition on and with engine off, attempt to start engine. If engine starts, go to step 3). If engine does not start, check fusible links at battery and PCM fuse. If fusible links or PCM fuse are blown, repair short to ground.
2. If fusible links and PCM fuse are okay, turn ignition on and check power circuits to PCM, including keep alive memory and ignition feed. See appropriate wiring diagram in WIRING DIAGRAMS section for power terminal identification. If power is not available to power terminals of PCM, check for opens in power circuits. If power is available to PCM power terminals, check for poor PCM ground circuits, or replace faulty PCM.
3. If engine starts and MIL does not illuminate, turn ignition off. Disconnect PCM connectors. Turn ignition on and jumper PCM light driver terminal to ground using a test light. See appropriate wiring diagram in WIRING DIAGRAMS section for power terminal identification.
4. If MIL is now on, repair light driver terminal connections at PCM or replace faulty PCM. If MIL stays off when test light is used to ground light driver terminal, check for blown instrument panel fuse, faulty bulb, open in light driver circuit between PCM and bulb, driver circuit shorted to voltage, or an open in ignition feed to MIL.

3.1L, 3.4L & 3.8L

1. Perform self-diagnostic procedures first. See appropriate TESTS W/CODES article in the ENGINE PERFORMANCE section. Turn ignition off. Disconnect PCM connectors. Turn ignition on. If MIL did not come on, go to next step. If MIL came on, repair short to ground in circuit No. 419 (Brown/White wire). If circuit is okay, check for faulty instrument panel.
2. Check PROM for proper installation. If PROM is okay, replace PCM using original PROM. Reconnect PCM connectors. Install Tech 1 scan tester. Turn ignition on. Using scan tester, turn MIL off. If MIL turns off, system is okay. If MIL does not turn on, replace faulty PROM.

SUMMARY

If no faults were found while performing BASIC DIAGNOSTIC PROCEDURES, no trouble codes (or only intermittent ones) were found while performing DIAGNOSTIC CIRCUIT CHECK and driveability problems exist, proceed to H - TROUBLE SHOOTING - NO CODES article in the ENGINE PERFORMANCE section for diagnosis by symptom (i.e., ROUGH IDLE, NO-START, etc.) or intermittent diagnostic procedures.

3.1L W/3-Speed A/T (VIN M) PCM Wiring Diagram (Grand Prix - 1 Of 2). Scheme 161

3.1L W/3-Speed A/T (VIN M) PCM Wiring Diagram (Grand Prix - 2 Of 2). Scheme 162

3.1L W/4-Speed A/T (VIN M) PCM Wiring Diagram (Cutlass Supreme, Grand Prix, Lumina, Monte Carlo & Regal - 1 Of 2). Scheme 163

3.1L W/4-Speed A/T (VIN M) PCM Wiring Diagram (Cutlass Supreme, Grand Prix, Lumina, Monte Carlo & Regal - 2 Of 2). Scheme 164

3.4L (VIN X) PCM Wiring Diagram (Cutlass Supreme, Grand Prix, Lumina & Monte Carlo - 1 Of 3). Scheme 165

3.4L (VIN X) PCM Wiring Diagram (Cutlass Supreme, Grand Prix, Lumina & Monte Carlo - 2 Of 3). Scheme 166

3.4L (VIN X) PCM Wiring Diagram (Cutlass Supreme, Grand Prix, Lumina & Monte Carlo - 3 Of 3). Scheme 167

3.8L (VIN L) PCM Wiring Diagram (Regal - 1 Of 3). Scheme 168

3.8L (VIN L) PCM Wiring Diagram (Regal - 2 Of 3). Scheme 169

3.8L (VIN L) PCM Wiring Diagram (Regal - 3 Of 3). Scheme 170