Engine Controls - Basic Testing Buick Skylark VII

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 135

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 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 136) 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 136)
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.

Scheme 136

NO START - ENGINE CRANKS OKAY (2.3L WITH IDI)

Note. Ensure battery is fully charged and check engine cranking speed and fuel supply before performing following tests.

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

1. Check fuel pump/injector (F/P INJ) fuse. Scan TP sensor signal. If scan voltage is greater than 1.0 volts, see Code 21 chart. Scan ECT sensor temperature. Scan temperature should be close to ambient temperature. If not, see Code 14 or 15 chart. Scan MAP sensor. Reading should be greater than 4 volts. Scan 7X reference pulse or crank RPM while cranking engine. If reference pulses are not displayed and RPM indicates zero, go to step 11). If all parameters are met, go to next step.
2. Disconnect all injector harness connector. Connect test light to injector harness connector No. 1 or 4. (Scheme 137) Crank engine and observe test light. Connect test light on injector harness connector No. 2 or 3. Crank engine. If test light flashes during both tests, go to next step. If neither light flashes during injector harness tests, go to step 16). If light flashes only on one connector, go to step 20). If light was on steady on one or both connectors, go to step 21).
3. Perform injector balance test. See FUEL CONTROL in I - SYSTEM & COMPONENT TESTING article in the ENGINE PERFORMANCE section. If injectors are okay, go to next step. If injectors are not okay, check for open or short in injector circuit. If circuit is okay, replace faulty injector.
4. Remove ignition coil and ignition control module assembly and install spark plug jumper wires. Using Spark Tester (ST-125), check for spark on all spark plugs one at a time. Remove spark plug boot from companion cylinder of ignition coil housing and install jumper wire from spark plug boot connector of ignition coil housing and ground (1-4 and 2-3).
5. Crank engine with remaining spark plug wires still connected. Spark should jump Spark Tester (ST-125) on all wires. If spark was not present, go to next step. If spark was present, check fuel pressure. Fuel pressure should be 41-47 psi (2.9-3.3 kg/cm 2 ). If fuel pressure is not as specified, check fuel system. If fuel pressure is as specified, check for wet/fouled spark plugs, binding TP sensor, contaminated fuel or low compression.
6. Turn ignition off. Disconnect spark plug jumper wires and remove ignition coil housing. Disconnect ignition coil harness connector at module. Connect test light to battery voltage and module terminals "B" and "C". Crank engine. Test light should flash at both terminals. If test light flashed, check faulty ignition coil connector or faulty ignition coil. If test light did not flash, go to next step.
7. Connect DVOM negative terminal to ground. Backprobe PCM connector terminal PC15. Check circuit frequency (Hz) while cranking engine. Repeat test on PCM connector terminal PB3. Frequency reading should be 1-10 Hz. If neither terminals showed frequency response, go to step 9). If only one showed frequency response, diagnose electronic ignition system. If both terminals showed frequency response, go to next step.
8. Disconnect ignition control module. Using DVOM, probe connector module terminals "A" and "B" to ground. Resistance should be 600-2600 ohms. If resistance is as specified, inspect ignition control module 11-wire connector. If connector is okay, replace ignition control module. If resistance is not as specified, repair open in circuit.
9. Turn ignition off. Disconnect Pink PCM connector. With DVOM connected to ground, check resistance in PCM terminals PB3 and PC15 (Achieva, Grand Am and Skylark) or PCM terminals J1-19 and J1-21 (Cavalier and Sunfire - M/T). Resistance should be greater than 5000 ohms on both circuits.
10. If resistance is as specified, go to next step. If resistance is not as specified, disconnect ignition control module 11-wire connector. Check resistance in PCM terminals PB3 and PC15 (Achieva, Grand Am & Skylark) or J1-19 and J1-21 (Cavalier & Sunfire - M/T) again. If reading is infinity, replace ignition control module. If reading is not infinity, repair shorted circuit No. 423 (White wire) or No. 406 (Black wire).
11. Turn ignition off. Connect DVOM between PCM terminal PB3 and PC15 (Achieva, Grand Am & Skylark) or J1-19 and J1-21 (Cavalier & Sunfire - M/T) and ground. Voltage reading should be zero. If voltage is not as specified, repair short to voltage in circuits No. 406 (Black wire) and No. 423 (White wire). If voltage is as specified, go to next step.
12. Turn ignition off. Check resistance between PCM terminals PB3 and PC15 and ground. Resistance should be infinite. If resistance is as specified, check PCM Pink connector. If connector is okay, replace PCM. If resistance is not as specified, check for short in circuits No. 423 and 406. If circuit is okay, replace ignition control module.
13. Turn ignition off. Disconnect ignition control module 11-wire connector. Turn ignition on. Connect test light between module connector terminals "K" and "L". (Scheme 137) If test light illuminates, go to next step. If test light does not illuminate, connect test light between ignition control module terminal "L" and ground. If test light illuminates, check open in circuit No. 750. If test light does not illuminate, check fuse or circuit No. 239 for open.
14. Connect DVOM between ignition control module terminals "F" and "J". (Scheme 137) Crank engine and observe DVOM voltage reading. If reading is greater than 200 millivolts, go to next step. If reading is less than 200 millivolts, go to step 17).
15. Turn ignition on. Install Tech 1 scan tester. Set scan tester to display 7X reference pulses. Connect test light to battery voltage. Touch and remove test light to ignition control module terminal "G". Scan tester should indicate 7X reference pulse increment when test light removed.
16. If scan tester displays reference pulse increment, inspect 11-wire module connector. If connector is okay, replace ignition control module. If scan tester does not display reference pulse, check circuit No. 430 for open or short to ground or voltage. If circuit is okay, replace PCM.
17. Remove crankshaft position sensor. Measure crankshaft position sensor resistance. Resistance should be 500-900 ohms. Ensure sensor is still magnetized. Replace defective crankshaft position sensor. If sensor is okay, repair sensor harness.
18. Remove injector test light. Using test light connected to ground, probe test light to injector harness terminal "A". Turn ignition off for 10 seconds. Turn ignition on. Test light should illuminate for 2-3 seconds or longer. If test light does not illuminate, go to next step. If test light illuminates, check injector driver circuits No. 467 and 468 for open or short to voltage. Repair circuits. If circuits are okay, replace PCM.
19. Disconnect 3-wire injector harness connector. Probe test light to injector harness terminal "B". (Scheme 137) Turn ignition off for 10 seconds. Turn ignition on. Test light should illuminate for 2-3 seconds or longer. If test light illuminates, repair open in circuit No. 120 or harness connector. If test light does not illuminate, go to next step.
20. Probe fuel pump test connector with test light connected to battery voltage. Turn ignition off for 10 seconds or longer. If test light illuminates, repair open in circuits No. 120 or 490. (Scheme 137) If test light does not illuminate, go to next step.
21. Turn ignition on. Test light should turn off for about 2 seconds and come back on again. If test light did not respond as indicated, check grounded circuit No. 120 between fuel pump power circuit and injectors. If test light turned off for 2 seconds and came back on, diagnose fuel pump or fuel pump circuit. Go to FUEL SYSTEM test.
22. Check injector driver circuits No. 467 and 468 for injector test light that did not illuminate. (Scheme 137) If circuit is okay, check Pink PCM connectors "C" and "D". If connectors are okay, replace PCM.
23. Check injector driver circuits No. 467 and/or 468 for injector test light that stayed on steady. (Scheme 137) If circuit is okay, replace PCM.

Fuel System

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. Check fuel pump relay fuse (FP/INJ). If fuse is okay, go to step 4). If fuse is blown, disconnect fuel pump harness connector. Ensure ignition is off. Using a test light connected to battery voltage, probe fuel pump test terminal. If test light illuminates, check for faulty fuel pump relay or shorted oil pressure switch. If test light does not illuminate, go to next step.
3. Remove fuel pump relay. Using a test light connected to battery voltage, probe fuel pump relay Pink wire terminal. If test light illuminates, check for shorted Pink wire. If test light does not illuminate, check for shorted fuel gauge assembly or faulty fuel pump.
4. Turn ignition off for 10 seconds. Turn ignition on. Fuel pump should run for about 2 seconds. If fuel pump was activated, diagnose fuel system. See BASIC FUEL SYSTEM CHECKS. If fuel pump did not come on, go to next step.
5. Turn ignition off. Using a fused jumper wire, jumper fuel pump test terminal to battery voltage. If fuel pump operates, go to step 7). If fuel pump did not operate, go to next step.
6. Disconnect fuel pump relay. Connect jumper wire to fuel pump relay Red wire terminal and battery voltage. If fuel pump operates, check for faulty relay connector or faulty relay. If fuel pump did not operate, check for open in Gray wire from fuel pump relay connector and fuel pump. If circuit is okay, check for poor fuel pump ground circuit. If ground circuit is okay, replace fuel pump.
7. Connect test light between fuel pump relay Pink wire connector and ground. If test light does not illuminate, repair open in ground circuit to relay. If test light illuminates, go to next step.
8. Turn ignition off for 10 seconds. Connect test light between fuel pump relay connector Dark Green/White wire terminal and ground. Test light should illuminate for about 2 seconds after ignition is turned on. If test light does not illuminate, go to next step. If test light illuminates, replace fuel pump relay.
9. Disconnect PCM connector and check for open or short in Dark Green/White wire. If circuit is not as specified, go to next step. If circuit is as specified, check resistance across fuel pump relay Black/White wire and Dark Green/White wire terminals. Resistance should be 20 ohms or greater. If resistance is as specified, replace PCM. If resistance is not as specified, replace relay and recheck resistance.
10. Repair Dark Green/White wire. If circuit was shorted to ground, recheck if test light illuminates between Dark Green/White wire terminal and ground within 2 seconds after ignition is turned on. If test light illuminates, reconnect PCM and relay. If test light does not illuminate, check for faulty PCM connector or faulty PCM.

Scheme 137

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 138) 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 138

Scheme 139

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 140) 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 140

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 from IDI module (if equipped). A shorted tachometer will not allow vehicle to start. Temporarily remove IDI assembly and install spark plug Jumper Wires (J-36012). Check for adequate spark with Spark Tester (ST-125). Check for spark on 2 adjacent plug wires (1-2 or 3-4, not 2-3). 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 leads from ignition coil. Using an ohmmeter, check ignition coil secondary resistance (secondary tower-to-secondary tower). Secondary resistance should be less than 10,000 ohms. Ignition coil primary resistance value is not supplied by manufacturer. If ignition coil is suspected of causing misfire or no-spark condition, switch coil locations on ignition module. If problem follows questionable coil, replace ignition coil.

1. Set DVOM on the 2000-ohm scale. Connect leads to crank angle sensor installed in side of engine block. Crankshaft sensor resistance should be 500-900 ohms on all models. If resistance is not as specified, replace sensor.
2. With sensor installed in block, connect one ohmmeter lead to either sensor terminal. Touch other ohmmeter lead to engine block. No continuity should exist. If continuity exists, sensor is shorted to ground and must be replaced.

Crank Angle Sensor Signal

Set DVOM on the 2-volt AC scale. Connect voltmeter leads to crank angle sensor, located on side of engine block. Crank engine and observe voltmeter reading. Crank angle sensor should generate a voltage signal of about .01 volt at slow cranking speed to greater than .02 volt (20 mV) at high cranking speed.

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. If tach pulse signal is not present, vehicle will not run. 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 141) 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 138) 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 141

Scheme 142

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»(/buick/skylark/vii-1992-1998/remont/testing-diagnostics/#engine-controls-basic-testing) 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.

2.3L

1. Install Tech 1 scan tool to Data Link Connector (DLC). Turn ignition on, with engine off. Check Malfunction Indicator Light (MIL). If MIL is on, go to next step. If MIL is off, see «A-1, MIL INOPERATIVE»(/buick/skylark/vii-1992-1998/remont/testing-diagnostics/#engine-controls-basic-testing__a-1-mil-inoperative) .
2. Observe Tech 1 scan tool display for scan data. Is scan data displayed? If yes, go to next step. If no DLC or scan data is displayed, check serial data circuit (Tan wire) for open, short to ground or short to voltage. See «WIRING DIAGRAMS»(/buick/skylark/vii-1992-1998/remont/testing-diagnostics/#engine-controls-basic-testing) . Repair as necessary. If serial data circuit is okay, replace faulty PCM or EPROM.
3. Using scan tool, command MIL on and off. Does MIL turn on and off when commanded? If no, go to next step. If yes, check for DTCs. If DTC(s) is present, diagnose affected DTC(s). Refer to appropriate SELF-DIAGNOSTICS article. If no DTC(s) is present, system is okay.
4. Turn ignition off. Disconnect PCM harness connectors. Turn ignition on. Observe MIL. If MIL is off, repair short to ground in MIL circuit (Brown/White wire) to PCM connector. See «WIRING DIAGRAMS»(/buick/skylark/vii-1992-1998/remont/testing-diagnostics/#engine-controls-basic-testing) . If MIL is on, go to next step.
5. Turn ignition off. Check EPROM for proper installation. If installation is okay, replace PCM using original EPROM. Turn ignition on, with engine off. Using scan tool, command MIL on and off. If MIL turns on and off as commanded, system is okay. If MIL does not turn on and off as commanded, replace EPROM.

3.1L

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.

2.3L (VIN D) PCM Wiring Diagram (Achieva, Grand Am & Skylark - 1 Of 3). Scheme 143

2.3L (VIN D) PCM Wiring Diagram (Achieva, Grand Am & Skylark - 2 Of 3). Scheme 144

2.3L (VIN D) PCM Wiring Diagram (Achieva, Grand Am & Skylark - 3 Of 3). Scheme 145

3.1L (VIN M) PCM Wiring Diagram (Achieva, Grand Am & Skylark - 1 Of 2). Scheme 146

3.1L (VIN M) PCM Wiring Diagram (Achieva, Grand Am & Skylark - 2 Of 2). Scheme 147

See also:
• WIRING DIAGRAMS
• A-1, MIL INOPERATIVE