Engine Controls - Basic Testing Buick Roadmaster VIII

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.

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

A & C CHART REFERENCE

Note. The following table provides the location of commonly used diagnostic information. These former "A" and "C" charts are now written in text and inserted into the appropriate location in the new Engine Performance workflow. To familiarize yourself with the Engine Performance workflow, see AA - USING THIS SECTION (GENERAL HELP INFORMATION) article in this section.

A & C CHART REFERENCE

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 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.
2. Check At O2 Sensor Remove O2 sensor. Install backpressure tester in place of O2 sensor. After test is completed, coat O2 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.

ECM REPLACEMENT CHECK

Many test procedures and test charts in ENGINE PERFORMANCE lead to conclusion that ECM is faulty. Before replacing ECM, check driven circuits and ECM Quad-Drivers (QDR) using following procedures and accompanying flow chart. (Scheme 3)

1. Using a DVOM, backprobe ECM 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 ECM 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, ECM is defective.
2. With DVOM still backprobing ECM at suspect circuit, ground ALDL "test" terminal "B". 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 ALDL "test" terminal is grounded. A "switching" operation should occur. Some TCC systems have pressure switches in series with TCC solenoid. On these applications, complete this circuit by disconnecting transmission/transaxle connector and using a standard test light in series between terminals "A" and "D" of connector.
3. If voltage drops and then floats back up, this occurs when QDR circuit is going into current limiting. Check the circuit current flow (.75 amp maximum, except as noted in QDR check chart). (Scheme 3) NOTE: For PCM-equipped vehicles, transmission/transaxle functions can only be energized through use of the TECH 1 scan tester. Shift solenoids on these models will not energize when ALDL is grounded.

Scheme 3

NO START DIAGNOSIS (A-3)

Note. Some vehicles are equipped with anti-theft systems (VATS or PASS-Key) which will not allow vehicle to be started if improper starting techniques 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 ECM 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 (1.9L SATURN)

Note. Check battery condition, 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 underhood Vehicle Emission Control Information label. Check ignition wires for cracking, hardness and proper connections at both distributor cap and spark plugs. Ensure each plug wire has less than 12,000 ohms resistance.
3. Remove spark plugs. Check and replace as necessary. Remove distributor cap and check for moisture, dust, cracks, burns and arcing to ground.
4. Try to turn distributor shaft by hand. Drive gear pin may be broken. In very cold temperatures, ensure oil is proper viscosity and not contaminated by gasoline.

Ignition System

1. Connect Spark Tester (ST-125) to end of one plug wire and crank engine. If spark occurs, check other wires. If spark occurs on all plug wires, check fuel delivery.
2. If spark is not present on all wires, connect scan tester to ALDL connector. Crank engine. If cranking RPM is not displayed on scan tester, go to step 6). If cranking RPM is displayed on scan tester, turn ignition off. Disconnect 6-wire connector at DIS ignition module.
3. Turn ignition on. Measure voltage between ground and connector Pink/Black ignition switch power supply wire. (Scheme 4) If battery voltage is present, go to next step. If battery voltage is not present, check DIS fuse. If fuse is okay, check for open in Pink/Black wire. If fuse is blown, check for short to ground in Pink/Black wire.
4. Turn ignition off. Disconnect 5-wire connector from DIS ignition module. Check resistance between ground and Black/White ground wire. If resistance is greater than 200 ohms, repair open in Black/White wire.
5. If resistance is less than 200 ohms, check for poor ignition module-to-connector harness contact. If okay, replace DIS ignition module.
6. If cranking RPM is not displayed on scan tester during cranking, turn ignition off. Disconnect 5-wire connector from DIS ignition module. Measure resistance between module harness Yellow and Purple wires (crankshaft position sensor terminals). (Scheme 4)
7. If resistance is not 700-900 ohms, go to step 10). If resistance is 700-900 ohms, set DVOM on AC volts scale. Connect leads between Yellow and Purple wires at 5-wire harness connector. Crank engine. If voltage is greater than.2 volt, go to next step. If voltage is not greater than.2 volt, check crankshaft position sensor wiring between sensor and DIS ignition module. If harness is okay, replace crankshaft position sensor.
8. Turn ignition off. Disconnect 6-wire DIS ignition module connector. Turn ignition on. Measure voltage between ground and Pink/Black ignition switch power supply wire of connector. If battery voltage is present, go to next step. If battery voltage is not present, check DIS fuse. If fuse is okay, check for open in Pink/Black wire. If fuse is blown, check for short to ground in Pink/Black wire.
9. Check DIS ignition module-to-harness connector contact. If connector is okay, replace DIS ignition module.
10. Remove crankshaft position sensor and measure sensor resistance. If resistance is not 700-900 ohms, replace crankshaft position sensor. If resistance is 700-900 ohms, ensure sensor is still magnetized. If sensor is not magnetized, replace sensor.
11. If sensor is still magnetized, check crankshaft position sensor harness for open or short to ground.

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. Connect Noid Light (SA9185E) for TBI or (SA9194E) for PFI to each injector. Crank engine. If light does not light at each connector, go to step 5). If light remains on constantly for any injector, go to step 4). If light flashes at each connector, check for resistance of 1-2 ohms at each injector.
3. If injector(s) resistance is not within specification, replace injector. If injector(s) resistance is within specification, check fuel quality.
4. If light is on constantly for any injector, turn ignition off. Disconnect PCM connector. Turn ignition on. If noid light is still on constantly, repair short to ground in injector drive circuit between injector harness connector and PCM. If noid light is no longer on with PCM disconnected, PCM is faulty.
5. Check 7.5-amp INJ fuse in underhood junction block. If fuse is okay, go to next step. If INJ fuse is blown, check for short to ground in injector power supply circuit.
6. Check for power to INJ fuse with ignition on. If power is not available to fuse, check for open in battery power supply to INJ fuse. If power is available to fuse, disconnect injector harness connector(s). Check for battery voltage on Pink/Black wire(s) of injector harness with ignition on. If power is present for each injector, go to next step. If power is not present, check for open circuit between fuse and injector harness connector.
7. Turn ignition off. Reconnect injector harness. Disconnect PCM connector. Turn ignition on. Check for battery voltage on injector drive circuit at PCM connector terminal J1D13 (TBI) or terminals J1D13, J1D14, J1D15 and J1D16 (PFI).
8. If battery voltage is not present, repair open injector drive circuit. If battery voltage is present, check injectors for 1-2 ohms resistance. Replace injectors if not within specification. If injectors are within specification, check for PCM-to-harness contact. If contact is okay, replace PCM.

Scheme 4

NO START - ENGINE CRANKS OKAY (TBI WITH HEI DISTRIBUTOR)

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

1. Ensure proper starting procedure is being used.
2. Visually check vacuum hoses for splits, kinks and proper connections, as shown on underhood Vehicle Emission Control Information label. Check ignition wires for cracking, hardness and proper connections at both distributor cap and spark plugs.
3. Remove spark plugs. Check and replace as necessary. Remove distributor cap and check for moisture, dust, cracks, burns and arcing to ground.
4. Try to turn distributor shaft by hand. Drive gear pin may be broken. In very cold temperatures, ensure oil is proper viscosity and not contaminated with gasoline.

1. Disconnect tachometer wire (if equipped) from tachometer terminal lead. A shorted tachometer or tachometer circuit will prevent vehicle from starting.
2. Connect Spark Tester (ST-125) to end of one plug wire and crank engine. Check at more than one wire. If spark occurs, check spark plugs and fuel delivery.
3. If spark does not occur, disconnect 4-wire EST connector at distributor. If spark now occurs, replace pick-up coil in distributor.
4. If spark does not occur, reconnect EST connector and connect Spark Tester (ST-125) to coil wire. Leave tester connected to coil wire for balance of tests or until problem is resolved. Crank engine. If spark occurs, check distributor cap for moisture, cracks or damage. If cap is okay, replace rotor.
5. If spark does not occur, disconnect 2-wire connector at distributor. Turn ignition on, with engine off. Check voltage between ground and harness terminals "+" and "C". (Scheme 5)or (Scheme 6).
6. If reading is less than 10 volts on terminal "C" only, check for open or ground in circuit between "C" terminal connector and ignition coil. If reading on both terminals is less than 10 volts, repair wire from "+" terminal of harness to terminal "B" of Black connector at coil.
7. If voltage at both terminals is greater than 10 volts, check voltage between ground and tachometer terminal of coil harness. If reading is 1-10 volts, replace ignition module and check for spark again. If spark does not occur, replace ignition coil.
8. If voltage reading at tachometer terminal is less than one volt, repair open or shorted tachometer lead or tachometer circuit. Repair tachometer lead or replace coil as necessary. If voltage reading at tachometer lead is greater than 10 volts, connect test light between ground and tachometer lead at coil. Crank engine and observe test light.
9. If test light is on steady, go to next step. If test light blinks, replace ignition coil and recheck for spark with tester. If there is still no spark, reinstall original coil and replace ignition module.
10. Disconnect distributor 4-wire connector. Remove distributor cap. Disconnect pick-up coil connector from module. Connect voltmeter from tachometer terminal to ground. Turn ignition on. Connect positive end of a known good 1.5-volt test battery to terminal "P" of module.
11. Observe reading on voltmeter connected to tachometer lead as negative end of test battery is momentarily grounded to distributor housing. If voltage reading on voltmeter does not drop, check ignition module ground. If ground is okay, replace ignition module.
12. If voltage reading on voltmeter drops, check for spark from coil wire as jumper to negative end of test battery is removed from distributor housing ground. If spark does not occur, go to step 14).
13. If spark occurs, ensure rotating pole piece in distributor is magnetized. If pole piece is not magnetized, replace pole piece and shaft assembly. If pole piece is magnetized, check pick-up coil connections and ensure pick-up coil resistance is 500-1500 ohms and does not have continuity to ground.
14. Test ignition module using Module Tester (J-24642). If ignition module tester is unavailable, replace ignition coil and repeat step 10). If spark occurs, system is okay. If spark does not occur, reinstall original ignition coil. Check coil wire from distributor cap. If coil wire is okay, replace ignition module.

1. Prior to 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. Crank engine and watch for injector spray. If injector spray occurs, go to step 5). If no spray occurs, disconnect injector harness and check for battery voltage at harness. Battery voltage should be present on one of the injector terminals. If battery voltage is not present, check for blown injector power fuse. If battery voltage is present on both terminals, check for wires shorted to one another.
3. If battery voltage is present on only one terminal, connect injector test light to injector harness. Crank engine and note light. If light flashes, check for stored ECM codes. If no codes are present, refer to HARD START symptom in TESTS W/O CODES article in the ENGINE PERFORMANCE Section. If light does not flash, momentarily touch test light from battery voltage to ECM RPM reference terminal (circuit No. 430). (Scheme 5)or (Scheme 6).
4. Each time test light is removed from ECM RPM reference terminal, injector test light should flash. If test light does not flash, check for open in RPM reference wire or injector drive (ground) circuit or replace faulty ECM.
5. If injector spray occurred while cranking engine, disconnect injector harness and crank engine. If injector spray or leakage occurs, this could cause a no-start condition due to excessive fuel being delivered during cranking. Repair faulty injector or injector seal. If no spray or leakage occurs, refer to HARD START symptom in TESTS W/O CODES article in the ENGINE PERFORMANCE Section.

Scheme 5

Scheme 6

NO START - ENGINE CRANKS OKAY (4.9L WITH HEI DISTRIBUTOR)

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

1. Ensure proper starting procedure is being used.
2. Visually check vacuum hoses for splits, kinks and proper connections, as shown on underhood Vehicle Emission Control Information label. Check ignition wires for cracking, hardness and proper connections at both distributor cap and spark plugs.
3. Remove spark plugs. Check and replace as necessary. Remove distributor cap and check for moisture, dust, cracks, burns and arcing to ground through coil mounting screws or rotor.
4. Try to turn distributor shaft by hand. Drive gear pin may be broken. In very cold temperatures, ensure oil is proper viscosity and not contaminated with gasoline.

1. Disconnect White tachometer wire at distributor TACH (C-) terminal (if equipped). A shorted tachometer or tachometer circuit will prevent vehicle from starting.
2. Connect Spark Tester (ST-125) to end of one plug wire and crank engine. If spark occurs, check spark plugs and fuel delivery.
3. If spark does not occur, check a second wire. If no spark occurs, check voltage at BAT terminal at distributor while cranking engine. If reading is less than 7 volts, repair open circuit between BAT terminal and ignition switch.
4. If reading is greater than 7 volts, check voltage on TACH terminal with ignition on, engine off. If reading is 1-10 volts, replace module. Fabricate an HEI coil spark tester by trimming a spark plug boot and connecting it to Spark Tester (ST-125). (Scheme 7) Crank engine. If spark occurs, system is okay. If no spark occurs, replace ignition coil.
5. If reading at TACH terminal is less than one volt, repair faulty ignition coil connection or replace faulty ignition coil.
6. If voltage reading at TACH terminal of distributor is greater than 9.9 volts, remove and invert distributor cap with wires connected. Fabricate an HEI coil spark tester by trimming a spark plug boot and connecting it to Spark Tester (ST-125). (Scheme 7) Crank engine.
7. If spark occurs, check cap for cracks, water or other defects. Verify correct pick-up coil is used. Proper pick-up coil has a Black connector.
8. If spark does not occur, turn ignition off and disconnect pick-up coil leads from module. Turn ignition on. With voltmeter connected to distributor TACH terminal and fabricated coil spark tester connected, momentarily touch test light, connected to battery voltage, to ignition module terminal "P". (Scheme 8)
9. If voltage at TACH terminal does not drop, check ignition module ground and for open in wires from ignition coil to module. If all is okay, replace ignition module.
10. If voltage at TACH terminal drops, check for spark at spark tester as test light is removed from terminal "P". If spark does not occur, go to next step. If spark occurs, check distributor grounds for opens. Repair as necessary. If no opens are present, check pick-up coil connections and for 500-1500 ohms resistance at pick-up coil leads. Repair as necessary.
11. If spark does not occur, test ignition module with module tester. If module tests okay, check ignition coil wire. If module tester is not available, replace ignition coil and again touch terminal "P." If spark occurs, system is okay. If spark does not occur, reinstall original ignition coil and replace ignition module.

Scheme 7

Scheme 8

1. Prior to checking fuel system for a no-start condition, check ignition for proper spark. Check for proper fuel pump pressure and capacity. See BASIC FUEL SYSTEM CHECKS.
2. Disconnect injector harness. Turn ignition on and check for battery voltage at each injector harness. (Scheme 9)or (Scheme 10). Battery voltage should be present on one side of each injector connector. If battery voltage is not present, check for blown injector power fuse. If battery voltage is present on both injector terminals, check for wires shorted together.
3. If battery voltage is present on only one terminal, connect injector test light to injector harness. Crank engine and note light. Repeat on other injector connectors. If light flashes, check for stored ECM codes. If no codes are present, refer to HARD START symptom in TESTS W/O CODES article in the ENGINE PERFORMANCE Section.
4. If light does not flash, disconnect distributor 5-wire connector. Momentarily touch test light from battery voltage to PCM RPM reference wire (circuit No. 430) of 5-wire connector. Each time test light is removed from PCM RPM reference terminal, injector test light should flash. If test light does not flash, check for open in RPM reference wire or injector drive (ground) circuit or replace faulty PCM.

Scheme 9

Scheme 10

NO START - ENGINE CRANKS OKAY (2.0L PFI WITH DIS)

Note. Check battery, engine cranking speed and fuel supply before performing the 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.
2. Check ignition wires for cracking, hardness and proper connections at both coil pack and spark plugs. In very cold temperatures, ensure oil is proper viscosity and not contaminated with gasoline.

1. Install scan tester. Check for stored ECM trouble codes. Scan TPS voltage. If TPS reading is less than.2 volt or greater than 2.5 volts, use Code 21 chart first. Scan CTS temperature. If scanned coolant temperature is less than -38°C, use Code 14 chart first. See appropriate TESTS W/CODES article in the ENGINE PERFORMANCE Section. Scan RPM on scan tester while cranking engine. If no RPM is displayed, go to step 6).
2. If all parameters scan okay, probe fuel pump test connector (Red wire located behind left front shock tower) with a test light connected to battery voltage. With ignition off, test light should be on. Turn ignition on. Test light should go out for about 2 seconds and then come back on. If test light functions as described, go to next step. If not, check fuel pump relay power supply, driver circuit and windings.
3. Using Spark Tester (ST-125), check for spark on spark plug wires 1 and 2, or 3 and 4. Check one wire at a time, leaving other wires connected during cranking. If spark does not occur on both plug wires, go to step 6). If spark occurs on both wires, turn ignition off. Disconnect 3-wire injector harness connector. Using DVOM, measure resistance between Black/Red wire and Light Blue wire on injector side of harness. (Scheme 11) Measure resistance between Black/Red wire and Light Green wire on injector side of harness. Resistance should be 5.9-6.3 ohms.
4. If resistance is within specification during both measurements, go to next step. If resistance during either measurement is less than 5.9 ohms, repair short in harness or replace any injector which measures less than 11.8 ohms when measured individually with harness connector removed. If resistance during either measurement is greater than 6.3 ohms, repair open in harness or replace any injector which measures greater than 12.6 ohms when measured individually with harness connector removed.
5. Reconnect 3-wire injector harness connector. Install injector test light in injector No. 1 harness connector. Crank engine. Transfer injector test light to injector No. 3 harness connector. Crank engine. If injector test light does not flash when installed in one or both injector harness connectors, go to step 10). If injector test light flashes when installed in injector No. 1 and No. 3 harness connectors, recheck fuel pressure. Also check for fouled spark plugs, EGR valve stuck open and a shorted A/C pressure sensor as possible causes for a no-start condition. CAUTION: When probing DIS circuits, ensure hands and clothing do not come into contact with rotating engine belts and pulleys.
6. If not previously done, using Spark Tester (ST-125), check for spark on spark plug wires No. 1 and 2 or, 3 and 4. Check one wire at a time, leaving other wires connected during cranking. If no spark is present, go to step 8). If spark occurs on one wire, turn ignition off. Check plug wire and replace if necessary. If wire is okay, disconnect 4-wire connector at ignition module.
7. With voltmeter set on DC volts and Black lead connected to ground, probe harness terminal No. 3 and then No. 4 while cranking engine. If voltmeter reading is greater than one volt, coil module is faulty. If voltmeter does not read greater than one volt, check for open or short to ground on EST "A" and "B" circuits between ECM connector and ignition module connector. If circuits are not open or shorted to ground, problem is poor ECM connections or faulty ECM.
8. If no spark was present in step 6), turn ignition off. Disconnect 4-wire ignition module connector. Turn ignition on. With test light connected to ground, probe 4-wire connector Pink/Black wire terminal. If test light is not on, repair open in ignition module power supply circuit. If test light is on, probe Black wire of 4-wire ignition module connector with test light connected to battery voltage. If test light is on, go to next step. If test light is not on, repair open in ignition module ground circuit.
9. With voltmeter set on DC volts and Black lead connected to ground, probe harness terminal No. 3 and then No. 4 while cranking engine. If voltmeter reading is greater than one volt, coil module is faulty. If voltmeter does not indicate greater than one volt, check for open or short to ground on EST "A" and "B" circuits between ECM connector and ignition module connector. If circuits are not open or shorted to ground, ECM connections are poor or ECM is faulty.
10. If light did not come on at one or both injector harness terminals, go to next step. If light was on steady on one or both injector harness terminals, turn ignition off. Disconnect ECM connectors and all injector connectors. With a test light connected to battery voltage, check injector drive circuits for short to ground. Repair as necessary. If no shorts to ground are present, problem is faulty ECM connections or faulty ECM.
11. Turn ignition on. Remove injector test light from injector harness. Probe Black/Red wire terminal of injector No. 1 or No. 3 harness connector with a test light connected to ground. If test light is not on, repair open in injector power supply circuit. If test light is on, turn ignition off. Reconnect all injector harness connectors. Disconnect ECM connectors.
12. Turn ignition on. Probe ECM harness connector terminals C12 and C15 with a test light connected to ground. If test light is not on at both terminals, repair open in injector drive circuits between injector harness connector and ECM harness connector. If test light is on at both ECM terminals, turn ignition off. Disconnect all 4 injector connectors. Turn ignition on. Again probe ECM connector terminals C12 and C15 with a test light connected to ground.
13. If light is on at either terminal, repair short to voltage in that circuit. If test light is not on at either terminal, ECM connections or ECM are faulty.

Scheme 11

NO START - ENGINE CRANKS OKAY (2.2L PFI WITH DIS)

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

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. Remove spark plugs. Check and replace as necessary.
4. In very cold temperatures, check oil is proper viscosity and not contaminated with gasoline.

1. Install scan tester. Check for stored ECM trouble codes. Scan TPS voltage. If TPS reading is less than.2 volt or greater than 2.5 volts, use Code 21 chart first. Scan CTS temperature. If scanned coolant temperature is less than -38°C, use Code 14 chart first. See appropriate TESTS W/CODES article in the ENGINE PERFORMANCE Section. Monitor RPM on scan tester while cranking engine. If no RPM is displayed, go to step 6).
2. If all parameters scan okay, probe fuel pump test connector (Red wire located behind left front shock tower) using a test light connected to battery voltage. With ignition off, test light should be on. Turn ignition on. Test light should go out for about 2 seconds and then come back on. If test light functions as described, go to next step. If test light does not function as described, check fuel pump relay power supply, driver circuit and windings.
3. Using Spark Tester (ST-125), check for spark on spark plug wires No. 1 and 2, or 3 and 4. Check one wire at a time, leaving other wires connected during cranking. If spark does not occur on both plug wires, go to step 6). If spark occurs on both wires, turn ignition off. Disconnect 2-wire injector harness connector. Using DVOM, measure resistance across harness terminals on injector side of harness. Resistance should be 2.9-3.1 ohms.
4. If resistance is within specification, go to next step. If resistance is less than 2.9 ohms, repair short in harness or replace any injector which measures 11.6 ohms or less when measured individually with injector harness connector removed. If resistance is greater than 3.1 ohms, repair open in harness or replace any injector which measures 12.4 ohms or greater when measured individually with injector harness connector removed.
5. Install injector test light in injector jumper harness connector (ECM side). Crank engine. If injector test light does not flash, go to step 12). If injector test light flashes, recheck fuel pressure. Also check for fouled spark plugs, EGR valve stuck open or a shorted A/C pressure sensor, any one of which could cause a no-start condition. CAUTION: When probing DIS circuits, ensure hands and clothing do not contact rotating engine belts and pulleys.
6. If not previously done, using Spark Tester (ST-125), check for spark on spark plug wires 1 and 2 or 3 and 4. Check one wire at a time, leaving other wires connected during cranking. If no spark is present, go to step 9). If spark occurs on one wire, go to step 8).
7. If spark is present on both wires, turn ignition off. Disconnect 6-wire ignition module connector. Turn ignition on. Monitor RPM on scan tester while repeatedly touching ignition module harness connector terminal "E" with a test light connected to battery voltage. If RPM is observed on tester, replace ignition module. If RPM is not displayed on tester, repair open or short to ground on RPM (high reference) input circuit between ECM connector and ignition module connector. If open or short is not present, problem is faulty ECM connections or faulty ECM.
8. If spark is present on one wire only, note which wire and coil has no spark. Turn ignition off. Remove ignition coil. Check for carbon tracking or faulty connections between coils and module. Replace coil if carbon tracking exists. If connections are okay and no carbon tracking exists, switch coil positions on module and retest for spark. If no-spark condition follows coil, replace faulty coil. If no-spark condition is still on original plug wire, replace ignition module.
9. If no spark was present in step 6), turn ignition off. Disconnect 2-wire ignition module connector. Turn ignition on. With test light connected to ground, probe 2-wire connector Pink/Black wire terminal. (Scheme 12), (Scheme 13), (Scheme 14) or (Scheme 15). If test light is not on, repair open in ignition module power supply circuit. If test light is on, probe Black/White wire of 2-wire ignition module connector with test light connected to battery voltage. If test light is on, go to next step. If test light is not on, repair open in ignition module ground circuit.
10. Turn ignition off. Disconnect 3-wire crankshaft sensor connector at ignition module. (Scheme 12), (Scheme 13), (Scheme 14) or (Scheme 15). Ensure resistance is 800-1200 ohms between Purple and Yellow wires of crankshaft sensor harness connector at ignition module. If resistance is within specification, go to next step. If resistance is less than 800 ohms, crankshaft sensor leads are shorted together or crankshaft sensor is faulty. If resistance is 1200 ohms or greater, check for open in Yellow or Purple wire or poor connections at crankshaft sensor. If no problems are found with sensor circuit or connections, crankshaft sensor is faulty.
11. With DVOM set on AC volts, connect voltmeter between Yellow and Purple wires of crankshaft sensor harness connector. Crank engine. If voltmeter reading is greater than.3 volt, ignition module is faulty. If voltmeter does not indicate greater than.3 volt, connections at crankshaft sensor are poor or crankshaft sensor is faulty.
12. If light did not come on at one or both injector harness terminals, go to next step. If light was on steady on one or both injector harness terminals, turn ignition off. Disconnect ECM connectors and all injector connectors. With a test light connected to battery voltage, check injector drive circuits for short to ground. Repair as necessary. If no shorts to ground are present, problem is faulty ECM connections or faulty ECM.
13. Turn ignition on. Remove injector test light from injector harness. Probe Pink/Black wire terminal of injector harness connector with a test light connected to ground. If test light is not on, repair open in injector power supply circuit. If test light is on, turn ignition off. Reconnect injector harness connector. Disconnect ECM connectors.
14. Turn ignition on. Probe ECM harness connector terminal A5 with a test light connected to ground. If test light is not on, repair open in injector drive circuits between injector harness connector and ECM harness connector. If test light is on, turn ignition off. Disconnect all 4 injector connectors. Turn ignition on. Again probe ECM connector terminal A5 with a test light connected to ground.
15. If light is on, repair short to voltage in that circuit. If test light is not on, problem is short or open in ECM peak and hold jumper, faulty ECM connections or faulty ECM.

Scheme 12

Scheme 13

Scheme 14

Scheme 15

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

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

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 ("J" & "L" Bodies)

1. Disconnect tachometer wire if equipped. A shorted tachometer or tachometer circuit will prevent vehicle from starting.
2. Install scan tester. Check for stored ECM trouble codes. Scan TPS voltage. If TPS reading is greater than 2.5 volts, use Code 21 chart first. Scan RPM while cranking engine. If RPM is displayed on scan tester, go to step 5). 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 plugs while cranking. If spark occurs on both wires, go to next step. If no spark occurs on either wire, go to step 11). If spark occurs on one wire only, go to step 4).
3. 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. If RPM is indicated on scan tester, problem is faulty ignition module-to-harness connection or faulty DIS ignition module. If RPM is not indicated, problem is open or short to ground in RPM reference circuit or faulty ECM.
4. 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 module is faulty.
5. Scan fuel pump signal (PPSW) during cranking. If voltage is not indicated, see Code 54 chart in appropriate TESTS W/CODES article in the ENGINE PERFORMANCE Section. If voltage is indicated, 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 plugs while cranking. If spark occurs on both wires, go to step 6). If spark does not occur on either wire, ignition module is faulty. If spark occurs on one wire, go to step 4).
6. If spark occurs on both wires, remove Blue and Green wire injector harness connectors. While cranking engine, probe each connector (ECM side) with test light connected to battery voltage. If both connectors do not cause test light to flash, go to next step. If both connectors cause test light to flash, recheck fuel system pressure. If fuel pressure is within specification, fuel injection system is okay. See HARD START symptom in TESTS W/O CODES article in the ENGINE PERFORMANCE Section.
7. If test light connected to injector harness connectors did not flash (no light), go to next step. If test light connected to either injector harness connectors is on steady, check injector drive circuit with steady light for short to ground. If circuit is not shorted to ground, ensure injector resistance is greater than 8 ohms (but not infinity). Replace any injector with less than 8 ohms resistance. If injectors are okay, ECM is faulty.
8. Turn ignition on. Probe injector harness terminals (injector side) with test light connected to ground. If test light is on at both terminals, go to next step. If light is off at both terminals, repair open in injector power supply circuit. Since injectors are wired in parallel, if light is on at one terminal only, problem is in harness which did not light.
9. Reconnect both injector harness connectors. Turn ignition off. Disconnect ECM connectors. Turn ignition on. Probe ECM harness terminals BC11 and BC12 using test light connected to ground. (Scheme 16)or (Scheme 17). If test light is off, repair open in circuit which did not light. If test light is on at both terminals, turn ignition off. Disconnect all injector connectors. Turn ignition on. Probe Blue and Green wires (ECM side of injector harness) using test light connected to ground. If test light is off, go to next step. If test light is on, repair short to voltage in that circuit.
10. Check resistance between injector harness terminals "A" and "C", "A" and "D", "B" and "D" and "B" and "C". If resistance is less than 4 ohms, check harness wires for short to each other and check individual injector resistance with injector connectors removed. Resistance should be 8 ohms or more (but not open). If no short to voltage is found, no injector harness wires are shorted together and no injector has improper resistance, replace ECM.
11. If no spark is present and RPM is not indicated on scan tester, as determined in step 2), turn ignition off. Disconnect 2-wire connector at ignition module. Turn ignition on. Connect test light across harness connector terminals. If test light is on, go to step 13). If test light is off, probe terminal "B" of harness connector with test light connected to ground.
12. If test light is off, repair open in ignition module power feed circuit. If test light is on, repair open in ignition module ground circuit wire between terminal "A" and engine ground.
13. Disconnect crankshaft sensor 3-wire connector at ignition module. Using ohmmeter, check resistance between Purple and Yellow wires of 3-wire harness connector. If resistance is 900-1200 ohms, go to next step. If resistance is less than 900 ohms, crankshaft sensor leads are shorted together or crankshaft sensor is faulty. If resistance is greater than 1200 ohms, repair open in Purple or Yellow wire between harness connector and crankshaft sensor or replace faulty crankshaft sensor.
14. Set voltmeter on 2-volt AC position. Crank engine with voltmeter leads connected between Purple and Yellow wires of crankshaft sensor harness. If voltmeter reading is not greater than.1 volt, problem is faulty connection at crankshaft sensor or faulty sensor. If voltmeter reading is greater than.1 volt, replace DIS ignition module.

Scheme 16

Scheme 17

Ignition System ("W" Body Except 3.1L Calif.)

1. Disconnect tachometer wire if equipped. A shorted tachometer or tachometer circuit will prevent vehicle from starting.
2. Install scan tester. Check for stored ECM trouble codes. Scan TPS voltage. If TPS reading is greater than 2.5 volts, use Code 21 chart first. Scan RPM while cranking engine. If RPM is displayed on scan tester, go to step 5). 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 plugs while cranking. If spark occurs on both wires, go to next step. If no spark occurs on either wire, go to step 9). If spark occurs on one wire only, go to step 4).
3. 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. If RPM is indicated on scan tester, problem is faulty ignition module-to-harness connection or faulty DIS ignition module. If RPM is not indicated, problem is open or short to ground in RPM reference circuit or faulty ECM.
4. 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 module is faulty.
5. Scan fuel pump signal (PPSW) during cranking. If voltage is not indicated, see Code 54 chart in appropriate TESTS W/CODES article in the ENGINE PERFORMANCE Section. If voltage is indicated, 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 plugs while cranking. If spark occurs on both wires, go to step 6). If spark does not occur on either wire, ignition module is faulty. If spark occurs on one wire, go to step 4).
6. If spark occurs on both wires, disconnect No. 1 and No. 6 injector harness connectors. Turn ignition on. With test light connected to ground, probe Pink/Black wires of injector harness connectors. (Scheme 18) If light is not on, repair open in injector power supply wire. If test light is on, connect test light to battery voltage. While cranking engine, probe Light Blue wire of injector harness connector. If test light does not flash, go to next step. If test light does flash, recheck fuel system pressure. If fuel pressure is within specification, fuel injection system is okay. See HARD START symptom in TESTS W/O CODES article in the ENGINE PERFORMANCE Section.
7. If test light connected to injector harness connector does not flash (no light), go to next step. If test light connected to injector harness connector is on steady, check injector drive circuit for short to ground. If circuit is not shorted to ground, ensure injector resistance is 12.0-12.4 ohms. Replace any injector that does not measure correct resistance. If injectors are okay, ECM is faulty.
8. Check for open or short to battery voltage in injector drive circuit between ECM and injector harness connector. If no problem exists in injector drive circuit, problem is faulty ECM.
9. If no spark is present and RPM is not indicated on scan tester as determined in step 2), turn ignition off. Disconnect 2-wire connector at ignition module. Turn ignition on. Connect test light across harness connector terminals. If test light is on, go to step 11). If test light is off, probe terminal "B" of harness connector using test light connected to ground.
10. If test light is off, repair open in ignition module power feed circuit. If test light is on, repair open in ignition module ground circuit wire between terminal "A" and engine ground.
11. Disconnect crankshaft sensor 3-wire connector at ignition module. Using ohmmeter, check resistance between Purple and Yellow wires of 3-wire harness connector. If resistance is 900-1200 ohms, go to next step. If resistance is less than 900 ohms, crankshaft sensor leads are shorted together or crankshaft sensor is faulty. If resistance is greater than 1200 ohms, repair open in Purple or Yellow wire between harness connector and crankshaft sensor, or replace faulty crankshaft sensor.
12. Set voltmeter on 2-volt AC position. Crank engine with voltmeter leads connected between Purple and Yellow wires of crankshaft sensor harness. If voltmeter reading is not greater than.1 volt, problem is faulty connection at crankshaft sensor or faulty sensor. If voltmeter reading is greater than.1 volt, replace DIS ignition module.

Scheme 18

Ignition System (3.1L Calif. "W" Body)

1. Disconnect tachometer wire (if equipped). A shorted tachometer or tachometer circuit will prevent vehicle from starting.
2. Install scan tester. Check for stored ECM trouble codes. Scan TPS voltage. If TPS reading is greater than 2.5 volts, use Code 21 chart first. Scan RPM while cranking engine. If 3X RPM signal is displayed on scan tester, go to step 5). 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 plugs while cranking. If spark occurs on both wires, go to next step. If no spark occurs on either wire, go to Code 82 chart in appropriate TESTS W/CODES article in the ENGINE PERFORMANCE Section. If spark occurs on one wire only, go to step 4).
3. 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. If RPM is indicated on scan tester, problem is faulty ignition module-to-harness connection or faulty ignition module. If RPM is not indicated, problem is open or short to ground in RPM reference circuit or faulty ECM.
4. If spark occurs on one wire only, check pair of wires for plug that did not spark. Ensure each wire measures 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 module is faulty.
5. Scan fuel pump signal (PPSW) during cranking. If voltage is not indicated, see Code 54 chart in appropriate TESTS W/CODES article in the ENGINE PERFORMANCE Section. If voltage is indicated, check fuel system pressure. See BASIC FUEL SYSTEM CHECKS. If fuel pressure is within specification, go to next step.
6. Disconnect No. 1 or 6 injector harness connector. Turn ignition on. With test light connected to ground, probe Pink/Black wires of injector harness connectors. (Scheme 19) If light is not on, repair open in injector power supply wire.
7. If test light is on, disconnect Black 8-pin ECM mini-harness connector. Using a Tech 1 scan tester in INJECTOR BALANCE mode and a test light connected to battery voltage, probe terminals "A", "B", "C", "E", "F" and "G" on ECM side of harness while cycling corresponding injector. If test light comes on for each injector, go to step 9).
8. If test light does not come on, repair open in circuit that did not light or check for poor ECM connection. If wiring and connections are okay, replace ECM.
9. Turn ignition on with engine off. With test light connected to ground, probe Black 8-pin ECM mini-harness connector terminals "A", "B", "C", "E", "F" and "G" on injector side of harness. If test light lights for each terminal, go to next step. If test light does not light for each terminal, repair open in circuit that did not light.
10. Check resistance of individual injectors. Resistance should be 11.8-12.6 ohms at room temperature. Replace any injector that is not within specification.

Scheme 19

Ignition System (3.4L "F" Body)

1. Disconnect tachometer wire (if equipped). A shorted tachometer or tachometer circuit will prevent vehicle from starting.
2. Install scan tester. Check for stored ECM trouble codes. Scan TPS voltage. If TPS reading is greater than 2.5 volts, use Code 21 chart first. Scan RPM while cranking engine. If 3X RPM signal is displayed on scan tester, go to step 5). If RPM is not displayed, check for spark on each coil (1-4, 2-5 or 3-6) using Spark Tester (ST-125). Check one wire at a time. Ground the companion cylinder plug wire while cranking. Leave the other 4 wires connected to spark plugs. If a crisp Blue spark occurs on all wires, go to next step. If no spark occurs on either wire, go to Code 82 chart in appropriate TESTS W/CODES article in the ENGINE PERFORMANCE Section. If spark occurs on one wire only, go to step 4).
3. Turn ignition off. Disconnect 6-wire ignition module connector. Turn ignition on. Monitor scanned RPM while momentarily touching RPM reference circuit wire (circuit No. 647) of ignition module harness connector with a test light connected to battery voltage. If RPM is indicated on scan tester, problem is faulty ignition module-to-harness connection or faulty ignition module. If RPM is not indicated, problem is open or short to ground in RPM reference circuit or faulty ECM.
4. If spark occurs on one wire only, check pair of wires for plug that did not spark. Ensure each wire measures 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 module is faulty.
5. Scan fuel pump signal (PPSW) during cranking. If voltage is not indicated, see Code 54 chart in appropriate TESTS W/CODES article in the ENGINE PERFORMANCE Section. If voltage is indicated, check fuel system pressure. See BASIC FUEL SYSTEM CHECKS. If fuel pressure is within specification, go to next step.
6. Disconnect injector No. 1 or 2 harness connector. Turn ignition on. With test light connected to ground, probe Pink/Black wires of injector harness connectors. (Scheme 20) If light is not on, repair open in injector power supply wire.
7. If test light is on, connect Injector Tester (J-32730-3C) to injector No. 1. Crank engine. Repeat test on remaining injectors. Test light should flash for each injector while engine is cranking. If test light flashes on all injectors, go to next step. If test light did not flash for all injectors, repair open in circuit that did not flash, check for faulty ECM connection on that circuit or replace faulty ECM.
8. At this point, no problem has been isolated for not start condition. A damaged crankshaft reluctor ring may cause a crank but will not run condition.

Scheme 20

NO START - ENGINE CRANKS OKAY (2.3L PFI 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.

Scheme 21

Scheme 22

1. Check fuel pump/injector (F/P INJ) fuse. Scan TPS signal. If scan voltage is not less than 2.5 volts, see Code 21 chart in TESTS W/CODES article in the ENGINE PERFORMANCE Section. Scan CTS temperature. If scan temperature is not -30°C to 130°C, see Code 14 or 15 chart in TESTS W/CODES article in the ENGINE PERFORMANCE Section. Scan 2X reference pulse or RPM while cranking engine. If reference pulses are not displayed and RPM indicates zero, go to step 14).
2. Disconnect 3-wire injector harness connector and connect test light between Gray and Dark Blue wires on ECM side of harness. (Scheme 21)or (Scheme 22). Crank engine and observe test light. Connect test light between Gray and Dark Green wires on ECM side of injector harness. Crank engine. If light flashes during both tests, go to next step. If neither light flashes during injector harness tests, go to step 8). If light flashes only on one wire, go to step 12). If light was on steady on one or both wires, go to step 13).
3. With DVOM on 200-ohm scale, measure resistance between injector harness Gray and Dark Blue wires on injector side of harness. Measure resistance between injector harness Gray and Dark Green wires on injector side of harness. Measured resistance during both tests should be about.9-1.1 ohms. If resistance is within specification, go to step 5).
4. If resistance is not within specification for both measurements, remove crankcase ventilation liquid/vapor separator to gain access to injector connectors. Disconnect injector for circuit which was not within specification. (Scheme 21)or (Scheme 22). With DVOM on 200-ohm scale, injector resistance should be about 1.9-2.1 ohms. If resistance is not correct, replace injector(s) with incorrect resistance. If injectors are within specification, repair open, short or poor connection in injector harness.
5. Temporarily remove IDI assembly and install spark plug Jumper Wires (J-36012). Remove test light from injector harness. Check for adequate spark with Spark Tester (ST-125). While cranking engine, 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. If spark jumps tester on both plug wires, check fuel system pressure and capacity.
6. Turn ignition off. Disconnect plug wires, and remove coil housing. Disconnect coil harness connector at module, and install a test light between module terminal "A" and control terminal for coil which did not spark. (Scheme 21)or (Scheme 22).
7. Crank engine and note test light. If test light blinks at both test terminals, repair faulty harness, poor connection or replace faulty coil. If test light did not blink on both terminals, repair module connections or replace faulty module.
8. If test light did not flash on either test in step 2), remove test light from injector harness. Probe Gray wire of ECM side of injector harness with a test light connected to ground. Turn ignition off for 10 seconds. Turn ignition on. Test light should be on for at least 2-3 seconds. If light is on, go to step 14). If test light is not on, probe fuel pump test connector (Gray wire located in left rear corner of engine compartment) with test light connected to ground. Turn ignition off for 10 seconds. Turn ignition on. Test light should be on for at least 2-3 seconds.
9. If test light is on, repair open in injector harness power supply (Gray) wire. If test light is not on, check fuel pump/injector (F/P INJ) fuse. If fuse is blown, replace fuse. If fuse blows again, repair short to ground in fuel pump power supply circuit. If fuse is okay, turn ignition off. Disconnect fuel pump relay connector, and probe Dark Green/White wire of fuel pump relay (located at center of firewall in engine compartment) using test light connected to battery voltage.
10. Turn ignition on and note test light. If test light is not on, go to next step. If test light is on for 2-3 seconds, check fuel pump relay, relay power supply circuit and circuit between relay and fuel pump test connector and injector harness/fuel pump splice. If fuel pump relay is faulty, oil pressure switch should have energized fuel pump and injectors after extended cranking. Check oil pressure switch also.
11. If test light is not on, backprobe terminal BA11 at ECM with test light to battery voltage. Turn ignition on. If test light is on for 2-3 seconds, repair open in Dark Green/White wire between ECM and fuel pump relay. If test light is not on, problem is poor ECM connection or faulty ECM. Also, check ECM "ignition on" (battery voltage) signal to ECM terminal BA6, as this is the signal the ECM uses to initiate fuel pump relay 2-3 second enable.
12. If test light did not flash during one injector harness test, check/repair open injector drive circuit wire (Dark Blue or Dark Green) on circuit which flash did not occur. If drive circuits are okay, check for open in peak and hold jumper circuits at ECM (BD5, BD6, BC13 and BC15) or poor connection at ECM connector. If peak and hold jumpers and connections are okay, ECM is faulty.
13. If light was on steady on one or both harness tests, check/repair injector drive circuit wire (Dark Blue or Dark Green) which had steady light for short to ground. If circuit is not shorted to ground, ECM is faulty.
14. If no 2X pulses exist, or no RPM is scanned during cranking, turn ignition off. Disconnect 11-pin connector at module. Turn ignition on and connect test light between terminals "K" and "L" at harness. If test light is not on, repair open in module ground or power supply circuit.
15. If test light is on, install injector test light in any injector harness connector. Connect a test light to battery voltage and repeatedly touch to IDI module terminal "H". Injector test light should flash. If test light flashes, go to next step. If test light does not flash, check injector drive circuits for open or short to voltage. Repair as necessary. If drive circuits are okay, check for open of short to ground in 2X reference pulse circuit between ECM and ignition module terminal "H", or poor connection at ECM terminal BD8. If 2X circuit and ECM connection are okay, ECM is faulty.
16. Connect DVOM between terminals "B" and "C" of IDI module harness connector. Place DVOM on 2-volt AC scale. Crank engine and note voltage. Voltmeter should read greater than 20mV. If voltage is correct, replace IDI module. If voltage is not correct, remove crankshaft sensor from block. Measure sensor resistance. Resistance should be 500-900 ohms. Place a flat piece of metal on tip of sensor to verify sensor is still magnetized. Inspect sensor harness. Repair or replace as necessary.

NO START - ENGINE CRANKS OKAY (PFI 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.

Note. C(3)I ignition system on 3.8L engines may use one of 2 coil pack types. On type I ignition coil pack, 3 twin tower coils are combined into a single coil pack. Coil pack is mounted directly over the C(3)I ignition module. Each coil provides the spark for 2 simultaneously paired spark plugs. All 3 coils must be replaced as a unit. On type II ignition coil pack, 3 separate twin tower coils are independently mounted over the C(3)I ignition module. Each coil provides the spark for 2 simultaneously paired spark plugs. Each coil can be replaced separately.

Ignition System (3.3L)

1. Prior to checking ignition system, check fuel system for cause of no start. See BASIC FUEL SYSTEM CHECKS. Ensure TPS scans less than 2.5 volts. If TPS does not scan less than 2.5 volts, see Code 21 chart in 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 CTS scan temperature. Disconnect tachometer wire (if equipped). A shorted tachometer or tachometer circuit will prevent vehicle from starting.
2. Disconnect all injector connectors and install one injector test light in one left bank injector harness connector and one in one of the right injector bank connectors. (Scheme 23)or (Scheme 24). Both lights should be off and should blink as engine is cranked. If either injector light is on steady, go to step 6). If lights do not blink at all, go to step 7). If both lights are off and they blink as engine is cranked, go to next step.
3. Check for adequate spark with 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 tester on all plug wires, disconnect all injectors and measure resistance of injector. Injector resistance should be 11.8-12.6 ohms at room temperature. All injectors should measure within.8 ohm of each other. If injectors are okay, check engine for mechanical problems. If spark did not occur on any plug wire, problem is poor ignition module connection or faulty ignition module.
4. If spark did not jump tester on one or 2 plug wires, verify that plug wire resistance is less than 30,000 ohms. Replace wires as necessary. If wires are okay, remove coil that did not fire. Connect a test light across ignition module terminals for problem coil.
5. 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. Also check primary coil resistance. If resistance is not.5-.9 ohm, replace coil.
6. Turn ignition off. Disconnect ECM Black C-D connector. Turn ignition on. If all lights are now off, replace ECM. If any lights are still on, repair short to ground in that injector drive circuit.
7. Remove injector test lights. Turn ignition on. Using a test light connected to ground, check for battery voltage on Pink/Black wire of injector harness. If test light is on, go to next step. If test light is off, check 20-amp 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 injector harness connector.
8. Turn ignition off. Disconnect ignition module connector. Turn ignition on. With test light connected to ground, check for battery voltage at ignition module harness connector terminal "M". If test light is not on, repair open in ignition module power supply. If test light is on, install injector test light in any injector harness connector. Connect test light to battery voltage and repeatedly touch terminal "D" of the ignition module harness connector. Injector test light should flash each time test light is touched to terminal "D". If injector test light flashes, go to step 10).
9. If injector test light does not flash, turn ignition off. Disconnect ECM Black C-D connector. Turn ignition on. Backprobe ECM injector drive terminals with a DVOM connected to ground. Battery voltage should be present at both driver terminals. If battery voltage is not present, repair open in that circuit. If battery voltage is present, problem is open or shorted circuit No. 430, poor connection at ECM injector driver terminals or faulty ECM.
10. Turn ignition off. Reconnect ignition module harness connector. Disconnect dual crank sensor connector. Turn ignition on. Using a DVOM, measure voltage between terminals "C" and "D" of sensor connector. If 10-12 volts is present, go to next step. If 10-12 volts is not present, problem is poor connection at ignition module connector, open or short to ground in circuit No. 644 or 645 or faulty ignition module.
11. Turn ignition off. Disconnect No. 6 plug wire from coil tower. NEVER crank engine with wire off of coil. Damage to coil or module may occur. Install Spark Tester (ST-125) onto spark plug wire. Clamp spark tester to coil tower. Install injector test light into any injector harness connector.
12. Jumper dual crank sensor harness connector terminals "A" and "B" together. Turn ignition on. DO NOT crank engine. Using a test light connected to ground, momentarily touch dual crank sensor harness terminal "A" while noting injector test light and spark tester.
13. If injector test light does not blink and spark tester does not have spark, problem is poor connection at ignition module or faulty ignition module. If injector test light flashes and spark tester has spark, problem is poor connection at dual crank sensor or faulty dual crank sensor. Inspect dual crank sensor and harmonic balancer interrupter rings for damage.

Scheme 23

Scheme 24

Ignition System (3.8L With Type I Coil Pack)

1. Ensure TPS scans less than 2.5 volts. If TPS does not scan less than 2.5 volts, see Code 21 chart in 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 CTS scan temperature. Disconnect tachometer wire if equipped. A shorted tachometer or tachometer circuit will prevent vehicle from starting. Disconnect cam sensor, and attempt to start engine. If engine starts, see Code 41 chart in TESTS W/CODES article in the ENGINE PERFORMANCE Section.
2. Compare scanned CTS temperature with actual coolant temperature. If they are not close, replace coolant sensor. Depress accelerator pedal approximately 25 percent. Attempt to start engine. If engine does not start, go to next step. If engine starts, check IAC counts on scan tester. Check for stored Code 35. Check for blocked IAC passages.
3. Disconnect all injector connectors and install injector test light in 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 6). If lights do not blink at all, go to step 7). If all lights are off and they blink as engine is cranked, check for adequate spark with 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 tester on all plug wires, check for fouled spark plugs or fuel system for cause of no-start. See BASIC FUEL SYSTEM CHECKS. If spark did not occur on any plug wire, problem is poor ignition module connection or faulty ignition module.
4. If spark did not jump tester on all plug wires, verify that plug wire resistance is less than 30,000 ohms. Replace as necessary. If wires are okay, remove 6 coil screws and tilt coil assembly back. Disconnect affected coil control wire from module.
5. Connect a test light between the common Blue wire and control wire of affected coil. 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. Also, check primary coil resistance (.5-.9 ohm). Replace coil if necessary.
6. Turn ignition off. Disconnect PCM Black C-D connector. Turn ignition on. If all lights are now off, replace PCM. If any lights are still on, repair short to ground in that injector drive circuit.
7. 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/Black wire of injector harness. If test light is on, go to next step. If test light is off, check 10-amp 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 injector harness connector.
8. Turn ignition off. Disconnect ignition module connector. Turn ignition on. Install injector test light in any injector harness connector. Connect test light to battery voltage and repeatedly touch terminal "D" of the ignition module harness connector (circuit No. 430). (Scheme 25)- (Scheme 27). Injector test light should flash each time test light is touched to terminal "D". If injector test light flashes, go to step 10).
9. 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 and short to voltage on fuel control circuit No. 430. If circuit is okay, connection at PCM fuel control terminal or PCM is faulty. CAUTION: In step 10), keep hands clear of pulleys and belts when jumpering sensor terminals. Slight belt/pulley movement may occur.
10. Turn ignition off, and reconnect ignition module connector. Disconnect crank sensor. Turn ignition on. Momentarily jumper crank sensor harness terminals "A" and "C." Reconnect crank sensor harness connector to sensor. DO NOT turn ignition off. Crank engine. If injector test light does not flash (DO NOT turn ignition off), go to next step. If injector test light flashes, check voltage to crank sensor harness terminal "D". If reading is more than 10 volts, check for poor crank sensor connections or replace faulty crank sensor. If reading is less than 10 volts, check for open or short to ground in power feed circuit (No. 644) to cam and crank sensors. If power circuit is okay, ignition module connection or ignition module is faulty. NOTE: Before replacing crank sensor, inspect sensor clearance. Clearance should be.025" (.625 mm). Check for signs of rubbing. If problem is evident, determine cause, and repair during sensor replacement.
11. If injector test light did not flash in step 10), check voltage between crank sensor harness terminals "A" and "C" using a DVOM. If 9-12 volts are present, go to step 13). If 9-12 volts are not present, check voltage from ground to crank sensor harness terminal "A". If 9-12 volts are not present, go to next step. If 9-12 volts are present, check sensor ground circuit No. 645 for an open. If circuit is okay, check for faulty ignition module connections or replace faulty ignition module.
12. Check crank sensor sync signal circuit for open or short to ground between crank sensor terminal "A" and ignition module terminal "H". Check ignition module power supply terminal "P" for poor connection. If circuits are okay, problem is faulty ignition module connection or faulty ignition module. CAUTION: In step 13), keep fingers and hands clear of pulleys and belts when jumpering sensor terminals. Slight belt/pulley movement may occur.
13. If 9-12 volts are present between terminals "A" and "C", turn ignition on. Momentarily jumper crank sensor harness terminals "A" to "C". Install a test light between fuel pump test connector and ground. For fuel pump test connector location, see COMPONENT LOCATIONS in I - SYS/COMP TESTS article in the ENGINE PERFORMANCE Section. Repeatedly jumper crank sensor harness terminal "B" to "C". As these 2 terminals are jumpered, test light on fuel pump test connector should flash. If test light does not flash, go to step 15).
14. If test light on fuel pump test connector flashed, check voltage between ground and terminal "D" of crank sensor harness connector. If reading is less than 10 volts, check crank and cam sensor power feed circuit (No. 644) for an open or short to ground. If circuit is okay, check for poor module connections or faulty ignition module. If volt-meter reading between ground and terminal "D" was 10 volts or more, check for poor crank sensor connections or faulty crank sensor.
15. If test light connected to fuel pump relay did not flash in step 13), check voltage between crank sensor harness terminals "B" and "C". If voltage is 9-12 volts, check for poor ignition module connections or replace faulty ignition module. If 9-12 volts are not present, check voltage from ground to crank sensor harness terminal "B". If 9-12 volts are not present, go to next step. If 9-12 volts are present, check ground circuit No. 645 for an open. If circuit is okay, check for faulty ignition module connections or replace faulty ignition module.
16. If 9-12 volts are not present from ground to crank harness terminal "B", check circuit No. 643 for open or short to ground or voltage. If circuit is okay, check for a damaged crank sensor. If sensor is okay, check for poor module connections or replace faulty ignition module.

Scheme 25

Scheme 26

Scheme 27

Ignition System (3.8L With Type II Coil Pack)

1. Ensure TPS scans less than 2.5 volts. If not, see Code 21 chart in TESTS W/CODES article in the ENGINE PERFORMANCE Section. Scan VATS enable with scan tester. If enable does not show YES, problem exists in VATS 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 CTS scan temperature. 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 41 chart in TESTS W/CODES article in the ENGINE PERFORMANCE Section.
2. Reconnect cam sensor connector. Compare scanned CTS temperature with actual coolant temperature. If they are not close, replace coolant sensor. Depress accelerator pedal approximately 25 percent. Attempt to start engine. If engine does not start, go to next step. If engine starts, check IAC counts on scan tester. Check for stored Code 35. Check for blocked IAC passages.
3. Disconnect all injector connectors and install injector test light in 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 6). If lights do not blink at all while cranking, go to step 7). If all lights are off and they blink as engine is cranked, 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 tester on all plug wires, check for fouled spark plugs or for fuel system as cause of no start. See BASIC FUEL SYSTEM CHECKS. If spark did not occur on any plug wire, ignition module connection is poor or ignition module is faulty.
4. If spark did not jump tester on all plug wires, verify that plug wire resistance is less than 30,000 ohms. Verify that 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 primary resistance of .3-.5 ohm. Replace coil if necessary. If coil is okay, connect a test light across ignition module terminals for problem coil.
5. 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.
6. Turn ignition off. Disconnect PCM Black C-D connector. Turn ignition on. If all lights are now off, replace PCM. If any lights are still on, repair short to ground in that injector drive circuit.
7. Check ignition module power supply (20-amp 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/Black wire of injector harness. If test light is on, go to next step. If test light is off, check 10-amp 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.
8. Turn ignition off. Disconnect ignition module connector. Turn ignition on. Install injector test light in any injector harness connector. Connect test light to battery voltage, and repeatedly touch terminal "D" of ignition module harness connector. Injector test light should flash each time test light is touched to terminal "D". If injector test light flashes, go to step 10).
9. 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. If circuit is okay, problem is faulty connection at PCM fuel control terminal or faulty PCM.
10. Turn ignition off. Using proper jumper adapter from Adaptor Kit (J-35616), connect a fused jumper 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 approximately 1.7 volts.
11. If voltage is high, check circuit No. 646 for open or short to ground. If open or short to ground is not present, 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.
12. If voltage is approximately 1.7 volts, move DVOM lead from terminal "H" to terminal "G". Crank engine and once again monitor voltage. Voltmeter should read about 5.5 volts. If voltage is correct, go to next step. If voltage is less than 5.5 volts, check for open or short to voltage in circuit No. 643. If voltage is greater than 5.5 volts, check for a short to ground on circuit No. 643. If no problem is found, crank sensor is faulty.
13. If voltage is close to 5.5 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.

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.

1. Scan VATS enable with scan tester. If enable does not show YES, problem exists in VATS system. Check for stored trouble codes. If Codes 16, 41 or 42 are set, use those code charts first. 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 CTS scan temperature. Compare scanned CTS temperature with actual coolant temperature. If they are not close, replace coolant sensor. Ensure TPS scans zero percent. If TPS does not scan zero percent, see Code 21 chart in appropriate TESTS W/CODES article in the ENGINE PERFORMANCE Section.
2. Scan engine RPM during cranking. If RPM is indicated on scan tester, go to step 4). If RPM is not indicated on tester, turn ignition off. Disconnect distributor electrical connector. Turn ignition on. Probe Yellow wire of distributor harness connector (ECM side) with a test light connected to ground. If test light is on, go to next step. If test light is not on, problem is faulty ECM connection, open or grounded ignition feed circuit (Yellow wire) or a faulty ECM.
3. Turn ignition off. Check for continuity between ground and distributor harness connector terminal "D" (Black/Pink wire). (Scheme 28)or (Scheme 29). If continuity exists, problem is faulty distributor connector connection or faulty distributor. If continuity does not exist, problem is faulty ECM connection, open ground circuit (Black/Pink wire) between ECM and distributor harness connector or faulty ECM.
4. Using Spark Tester (ST-125), check for spark on a plug wire while cranking engine. Check at a second wire. If spark does not occur, go to step 9). If spark does occur, crank engine with injector test light connected to each injector harness connector (one at a time). If light is on steady on any injector harness connector, go to next step. If light does not come on (no light) on any injector harness connector, go to step 6). If light blinks dimly, injector(s) is most likely shorted. Ensure injectors have at least 10 ohms resistance. If light blinks brightly on all injector harness connectors, check fuel system pressure. See BASIC FUEL SYSTEM CHECKS.
5. If injector test light is on steady when connected to any injector harness connector, check injector drive circuit of that injector for short to ground. If circuit is not shorted to ground, ensure injector resistance is at least 10 ohms (but not infinity). If circuit is okay and all injectors have at least 10 ohms resistance, ECM is faulty.
6. Turn ignition on. Probe each injector connector terminal (Dark Green, Pink/Black and Dark Blue wires) with a test light connected to ground. Since injectors are wired in parallel, light should be on both terminals of each injector. If test light is off at both terminals, repair open in injector power feed circuit. If test light is on at only one wire of an injector harness connector, problem is an open in tested harness.
7. If test light is on at both terminals of each injector harness connector, turn ignition off. Reconnect all injector connectors. Disconnect ECM connectors. Turn ignition on. Probe ECM harness connector terminals D10 and D11 with a test light connected to ground. If test light is on for both terminals, go to next step. If test light is off on either terminal, repair open in that circuit between ECM connector and injector harness connector.
8. Disconnect all injector connectors. Turn ignition on. Probe injector drive circuit Dark Blue and Dark Green wires on ECM side of injector harness using a test light connected to ground. Test light should not glow. If light is on, repair short to voltage on that circuit of harness. If harness is okay, ensure injector resistance is greater than 10 ohms (but not infinity). Replace injectors as necessary. Inspect injector harness connectors terminals for loose or backed-out pins. If no problems are found in this step, replace ECM.
9. Check spark at coil wire using Spark Tester (ST-125). Leave spark tester connected to coil for remaining steps. If spark does not occur, go to next step. If spark occurs, inspect distributor cap for cranks. Inspect secondary wiring (plug wires) for opens, shorts or poor connections. If cap and wires are okay, replace distributor.
10. If spark did not occur at coil wire, check for open or shorted coil wire. If coil wire is okay, disconnect ignition coil driver connector. Turn ignition on. With voltmeter negative lead connected to ground, check voltage between terminals "A" and "D" of coil driver harness. If voltage on one terminal is less than 10 volts, check for open or short or faulty coil connection on that circuit. If circuit and connection are okay, coil is faulty.
11. If voltage on both terminals is less than 10 volts, check for faulty power feed circuit to coil or grounded external coil circuit. If external circuits and power feed are okay, coil is faulty.
12. If voltage on both terminals is 10 volts or greater, connect DVOM set on AC scale to ground and terminal "B" of coil driver harness. Crank engine. If voltage is not 1-4 volts, go to step 14). If voltage is between one and 4 volts, probe coil driver connector terminal "C" with a test light connected to battery voltage.
13. If test light is not on, coil driver ground circuit is open. If test light is on, coil driver connection or coil driver is faulty.
14. Crank engine and monitor low resolution signal on scan tester. If low resolution signal is present, problem is faulty EST connection at ECM, open EST circuit or faulty ECM. If low resolution signal is not present, turn ignition off. Disconnect distributor electrical connector. Turn ignition on. Probe terminal "C" of distributor harness with a test light connected to ground. If test light is on, go to step 16).
15. If test light is off, problem is faulty ECM connection, open in ignition feed circuit between ECM and distributor harness connector terminal "C" or faulty ECM.
16. Turn ignition off. Check for continuity between ground and distributor harness connector terminal "D". If continuity exists, go to next step. If continuity does not exist, open ground circuit between ECM and distributor harness connector terminal "D", faulty ECM connection or faulty ECM.
17. Turn ignition on. Using DVOM set on AC scale, measure voltage on terminal "A" of distributor harness connector. If about 5 volts is present, go to next step. If about 5 volts is not present, problem is open or short in low resolution circuit between ECM and distributor harness connector terminal "A", faulty ECM connection or faulty ECM.
18. Measure voltage on terminal "B" of distributor harness connector. If about 5 volts are present, distributor connection or distributor is faulty. If about 5 volts are not present, problem is open or short in high resolution circuit between ECM and distributor harness connector terminal "B", faulty ECM connection or faulty ECM.

Scheme 28

Scheme 29

BASIC FUEL SYSTEM CHECKS (A-7)

Fuel Pressure Relief (TBI)

Disconnect negative battery cable. Remove fuel filler cap. Since these TBI units contain an internal bleed-down feature, after a short time, system fuel pressure should dissipate.

Fuel Pressure Relief (PFI)

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. On all models except 2.0L and 2.2L, install Fuel Pressure Gauge (J-34730-1) on fuel pressure connector of fuel rail. On 2.0L and 2.2L, install TBI Fuel Pressure Gauge (J-29658-D) using Adapter Kit (J-29658-100). Wrap shop towel around pressure connection when installing fuel pressure gauge to absorb fuel leakage. Install gauge bleed hose in container. Open bleed valve to bleed fuel pressure.

Fuel Pressure Check (TBI)

1. Remove air cleaner, and plug thermal vacuum port on throttle body. After shutting off engine, wait at least 2 minutes before connecting fuel pressure gauge. When removing fuel line, always use 2 wrenches. Install Fuel Pressure Gauge (J-29658B or BT-8205) and Adapter (J-29658-85) in fuel line between steel line and flexible hose.
2. Turn ignition on and observe fuel pressure reading. Fuel pressure should read 9-13 psi (.6-.9 kg/cm 2 ). If no fuel pressure is indicated, go to step 5). If fuel pressure is okay but engine will not start, go to NO START DIAGNOSIS. If fuel pressure is present but is too high, go to step 4). If fuel pressure is present but is too low, gradually pinch off fuel return line to fuel tank. NOTE: It should not be necessary to completely restrict fuel return line to observe a pressure increase. DO NOT damage return line.
3. If fuel pressure remains low, check for plugged fuel filter or restriction in fuel delivery line. If filter is okay and no restrictions are present, replace fuel pump. If fuel pressure increases when return line is pinched, replace fuel pressure regulator.
4. If fuel pressure is present but is higher than specification, check for restriction in fuel return line. If return line is not restricted, replace fuel pressure regulator.
5. If no fuel pressure is observed, turn ignition off. 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 - SYS/COMP TESTS article in the ENGINE PERFORMANCE Section. Observe fuel pressure reading. If fuel pressure is still not evident, 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 - SYS/COMP TESTS article in the ENGINE PERFORMANCE Section.
7. After all repairs, allow fuel pressure to dissipate. Remove fuel pressure gauge, and reconnect fuel line. Start engine and watch for fuel system leaks. For further details on fuel pressure testing, see I - SYS/COMP TESTS article in the ENGINE PERFORMANCE Section.

Fuel Pressure Check (PFI)

1. Relieve fuel pressure as previously described in FUEL PRESSURE RELIEF (PFI). On all models except 2.0L and 2.2L, connect Fuel Pressure Gauge (J-34730-1) to fuel pressure fitting on fuel rail. On 2.0L and 2.2L, install TBI Fuel Pressure Gauge (J-29658-D) using Adapter Kit (J-29658-100). This kit modifies TBI fuel pressure gauge so it may be installed in fuel delivery line with quick-disconnect fittings. With gauge installed, turn ignition on. With ignition on and engine off, pressure should read within specification. See FUEL PRESSURE (PFI) 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 I - SYS/COMP TESTS 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 - SYS/COMP TESTS 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 - SYS/COMP TESTS article in the ENGINE PERFORMANCE Section.

FUEL PRESSURE

Fuel Pump Relay

See MOTORS, RELAYS & SOLENOIDS in I - SYS/COMP TESTS article in the ENGINE PERFORMANCE Section.

Fuel Pump Relay By-Pass Procedure

See FUEL DELIVERY in I - SYS/COMP TESTS article in the ENGINE PERFORMANCE Section.

Fuel Pressure Relief (TBI & PFI)

Fuel pressure may be relieved by using one of the following methods

1. 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. Reconnect rear body connector.
2. Install Fuel Pressure Gauge (SA9127E1) on fuel pressure connector fitting at rear of engine. Wrap shop towel around pressure connection when installing fuel pressure gauge to absorb fuel leakage. Install gauge bleed hose in container. Open bleed valve to bleed fuel pressure.

Scheme 30

1. Relieve fuel pressure as previously described in FUEL PRESSURE RELIEF (TBI & PFI). With fuel gauge installed at fuel rail connector, turn ignition on. With ignition on and engine off, pressure should read within specification. See FUEL PRESSURE table. If no fuel pressure is present, go to step 5). If fuel pressure is less than specification, go to step 3). If pressure is within specification, turn ignition off. Pressure should hold. If pressure holds, system is functioning properly. If pressure does not hold, go to step 7).
2. If pressure is present but is greater than specification, check fuel return line for blockage by disconnecting return line and placing it into a container. Turn ignition on. If fuel pressure is still not within specification, replace fuel pressure regulator. If fuel pressure is within specification, repair blockage in fuel system return line.
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, turn ignition off. Bleed off fuel pressure. Install fuel return line plug, available with fuel pressure gauge kit. Apply battery voltage to fuel pump test connector gray wire using a 10-amp fused jumper wire. Fuel pump test connector is located in rear compartment on driver's side behind carpet. (Scheme 30) (Scheme 30): Fuel Pump Test Connector Component Location (Saturn)
4. 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 gray wire using a 10-amp fused jumper wire. Fuel pump test connector is located in rear compartment on driver's side behind carpet. (Scheme 30) 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 - SYS/COMP TESTS article in the ENGINE PERFORMANCE Section.
7. If pressure does not hold with ignition off, bleed off fuel pressure. Install fuel return line plug, available with fuel pressure gauge kit. Turn ignition on. Cycle key on and off several times to obtain accurate pressure reading. Allow pressure to stabilize for 30 seconds. Monitor fuel pressure reading for 5 minutes. Repeat test at least 2 more times.
8. Pressure drop in 5 minutes should not exceed 6-8 psi (.4-.6 kg/cm 2 ). If pressure does not hold, fuel pump check valve is bad, or injectors or fittings are leaking. To test fuel pump check valve, turn ignition off. Bleed off fuel pressure. Connect fuel pressure gauge to fuel delivery line. Close valve on pressure gauge.
9. Turn ignition on. Cycle key on and off several times to obtain accurate pressure reading. Allow pressure to stabilize for 30 seconds. Monitor fuel pressure for 5 minutes. Repeat test at least 2 more times. Pressure reading should be 58-94 psi (4.0-6.5 kg/cm 2 ) and should not leak down more than 6-8 psi (.4-.6 kg/cm 2 ). If no leakage is present, problem is leaking injectors or fittings. If pressure leakage is excessive, check for external leaks. If no leaks are present, check fuel pump and connections inside of fuel tank.

1. Relieve fuel pressure as previously described in FUEL PRESSURE RELIEF (TBI & PFI). With fuel gauge installed at fuel rail connector fitting, turn ignition on. With ignition on and engine off, pressure should read within specification. See FUEL PRESSURE table. If no fuel pressure is present, go to step 6). If fuel pressure is less than specification, go to step 4).
2. If pressure is present but is greater than specification, check fuel return line for blockage by disconnecting return line and placing it into a container. Turn ignition on. If fuel pressure is still not within specification, replace fuel pressure regulator. If fuel pressure is within specification, repair blockage in fuel system return line.
3. Start engine. Pressure should drop 3-10 psi (.2-.7 kg/cm 2 ). If pressure does not drop, check vacuum supply line to pressure regulator. If vacuum is present, replace pressure regulator. If pressure drops, turn ignition off. Pressure should hold. If pressure does not hold, go to step 8). If pressure holds, system is functioning properly.
4. If pressure is present but less than specification, check for restricted delivery line or fuel filter. Repair as necessary. If no restriction is evident, turn ignition off. Bleed off fuel pressure. Install fuel return line plug, available with fuel pressure gauge kit. Apply battery voltage to fuel pump test connector using a 10-amp fused jumper wire. Fuel pump test connector is located in rear compartment on driver's side behind carpet. (Scheme 30)
5. 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.
6. Apply battery voltage to fuel pump test connector using a 10-amp fused jumper wire. Fuel pump test connector is located in rear compartment on driver's side behind carpet. (Scheme 30) 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.
7. If fuel pressure is present with voltage applied to test connector, test fuel pump relay and voltage supply to relay. See I - SYS/COMP TESTS article in the ENGINE PERFORMANCE Section.
8. If pressure does not hold with ignition off, bleed off fuel pressure. Install fuel return line plug, available with fuel pressure gauge kit. Turn ignition on. Cycle key on and off several times to obtain accurate pressure reading. Allow pressure to stabilize for 30 seconds. Monitor fuel pressure reading for 5 minutes. Repeat test at least twice more.
9. Pressure drop in 5 minutes should not exceed 6-8 psi (.4-.6 kg/cm 2 ). If pressure does not hold, fuel pump check valve is bad, or injectors or fittings are leaking. To test fuel pump check valve, turn ignition off. Bleed off fuel pressure. Connect fuel pressure gauge to fuel delivery line. Close valve on pressure gauge.
10. Turn ignition on. Cycle key on and off several times to obtain accurate pressure reading. Allow pressure to stabilize for 30 seconds. Monitor fuel pressure for 5 minutes. Repeat test at least 2 more times. Pressure reading should be 58-94 psi (4.0-6.5 kg/cm 2 ) and should not leak down more than 6-8 psi (.4-.6 kg/cm 2 ). If no leakage is present, problem is leaking injectors or fittings. If pressure leakage is excessive, check for external leaks, If none are present, check fuel pump and connections inside of fuel tank.

FUEL PRESSURE

See FUEL DELIVERY in I - SYS/COMP TESTS article in the ENGINE PERFORMANCE Section.

See FUEL DELIVERY in I - SYS/COMP TESTS article in the ENGINE PERFORMANCE Section.

FIELD SERVICE MODE CHECK (EXCEPT PFI CADILLAC)

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. For field service mode check on PFI Cadillac vehicles, see appropriate TESTS W/CODES article in the ENGINE PERFORMANCE Section.

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 test terminal "B" of the ALDL diagnostic connector. (Scheme 31) In "closed loop" mode, SERVICE ENGINE SOON light will flash once a second.
2. In "open loop", light will flash 2.5 times a second. If light is off most of the time, a lean exhaust is indicated. If light is on most of the time, a rich exhaust is indicated.

Scheme 31

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 (Externally Mounted)

1. Remove coil connectors and secondary coil wire. In test "A", use high ohmmeter scale. (Scheme 32) Resistance value should be very high (infinite). If resistance is not infinite, replace coil.
2. In test "B", use low ohmmeter scale. Reading should be approximately zero ohms. If resistance is not approximately zero ohms, replace coil. In test "C", use high ohmmeter scale. If there is no continuity, replace coil.

Scheme 32

Ignition Coil Resistance (Internally Mounted)

1. Turn ignition off. Remove distributor cap and coil assembly. Invert cap. (Scheme 33) 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 33

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 opens 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 ALDL diagnostic connector. RPM should be indicated on tester when engine is cranked or running. If scan tester is unavailable, 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 circuit No. 430 ECM terminal with engine cranking.
2. A tach pulse signal may be simulated (to test ECM response) by connecting a test light in series between battery and circuit No. 430 ECM terminal. Each time test light is touched to and removed from circuit No. 430, ECM will see this as a tach signal. For circuit and terminal reference, see appropriate schematic under NO START - ENGINE CRANKS OKAY.

Hall Effect Switch (4.9L Cadillac)

1. Disconnect distributor 4-wire and 6-wire connectors. Apply battery voltage to Red wire of 3-wire distributor connector (distributor side). Connect ground to Black wire of 3-wire distributor connector (distributor side).
2. Connect voltmeter positive lead to terminal "E" (Brown/ White wire) of 5-wire distributor connector (distributor side). Connect voltmeter negative lead to terminal "D" (Black/Red wire) of 5-wire distributor connector (distributor side).
3. Bump starter and note voltmeter reading. When distributor blade is in window of Hall Effect switch, voltmeter should read within .5 volt of battery voltage. When distributor blade is not in window of Hall Effect switch, voltmeter should read less than .5 volt. Bump starter several time to cause both conditions to occur.
4. If Hall Effect switch is functioning properly and starter is cranked, voltmeter should show an averaged voltage of about 5-6 volts. If Hall Effect switch does not function as described, replace Hall Effect switch.

1. If factory tachometer is connected to 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 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 and check Pink/Black wire of ignition module for battery voltage. If battery voltage is not present, check ignition or ECM fuse. If fuse is not blown, check for open between fuse and ignition module.

Ignition Coil Resistance (Except 1.9L)

Ignition coil primary and secondary resistance values are not supplied by manufacturer. If ignition coil is suspected of causing misfire or no-spark condition, switch coil locations on DIS module. If problem follows questionable coil, replace original coil.

Ignition Coil Resistance (1.9L)

1. Disconnect ignition coil leads. Measure secondary coil resistance (secondary tower-to-secondary tower). Resistance should be 7000-10,000 ohms. If resistance is not within specification, replace ignition coil.
2. Ignition coil primary resistance value is not supplied by manufacturer. If ignition coil is suspected of causing a misfire or a no-spark condition, switch coil locations on DIS module. If problem follows questionable coil, replace original coil.

Crankshaft Sensor Pick-Up Coil Short & Resistance Checks

1. Set DVOM on the 2000-ohm scale. Connect leads to crank angle sensor connector, located on side of engine block. Turn ignition off. On all models except 2.0L, disconnect ignition module connectors. On 2.0L, disconnect ECM connectors. On 2.0L, measure resistance between ECM terminals D9 and D10. On all other models, 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 (ECM terminal D9 or D10 on 2.0L). 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 ALDL diagnostic connector. 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.

Ignition Coil Resistance

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 original 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 ALDL diagnostic connector. 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 ECM 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.

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 appropriate 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 ALDL diagnostic connector. 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 ECM terminal. For circuit and terminal reference, see appropriate schematic in NO START - ENGINE CRANKS OKAY.

Disconnect tachometer wire (if equipped). A shorted tachometer will not allow vehicle to start. Check for adequate spark with Spark Tester (ST-125). Check for spark on more than one plug wire. 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 coil. If battery voltage is not present, check for blown 10-amp COIL fuse. If fuse is not blown, check for open between fuse and ignition coil.

Information is not available from manufacturer.

Connect scan tester to ALDL diagnostic connector. Scan low and high resolution reference pulses. Both high and low pulses should be present when engine is cranking or running. If low resolution pulse is not present, engine will not start and ECM will set Code 16 in memory. If high resolution pulse is not present, vehicle will still run; however, ECM will set Code 36 in memory. 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 ADJUSTMENTS article in the ENGINE PERFORMANCE Section.

DIAGNOSTIC CIRCUIT CHECK (EXCEPT PFI CADILLAC)

Note. On PFI Cadillac vehicles, see appropriate TESTS W/CODES article in the ENGINE PERFORMANCE Section.

The Diagnostic Circuit Check determines

1. If SERVICE ENGINE SOON light works.
2. If ECM 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 34)and (Scheme 35). After performing necessary tests as described in the diagnostic circuit check, if no codes are indicated and driveability problems still exist, see TESTS W/O CODES article in the ENGINE PERFORMANCE Section and SCAN TESTER USAGE in TESTS W/CODES article in the ENGINE PERFORMANCE Section.

1. Check operation of SERVICE ENGINE SOON light. Turn ignition on with engine off. SERVICE ENGINE SOON light should be on steady. If light illuminates and stays on steady, go to next step. If light does not illuminate, go to A1, SERVICE ENGINE SOON LIGHT INOPERATIVE. If light flashes, go to step 3).
2. Grounding the ALDL test terminal "B" at this time should cause SERVICE ENGINE SOON light to flash a Code 12, followed by any codes stored in ECM memory. (Scheme 31) Light going from bright to dim is not considered a code. If light dims or remains on and does not flash Code 12, see A2, SERVICE ENGINE SOON LIGHT 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.
3. If light begins to flash as soon as ignition is turned on, check for a short to ground on the diagnostic test terminal wire between ALDL terminal "B" and ECM terminal No. 5. If circuit is okay, replace ECM.

Scheme 34

Diagnostic Circuit Check & Work Flow. Scheme 35

A1, SERVICE ENGINE SOON LIGHT INOPERATIVE

1. If SERVICE ENGINE SOON light does not illuminate with ignition on and engine off, attempt to start engine. If engine starts, go to step 3). If engine does not start, check fusible links at battery and ECM fuse. If fusible links or ECM fuse are blown, repair short to ground.
2. If fusible links and ECM fuse are okay, turn ignition on and check power circuits to ECM, including keep alive memory and ignition feed. See appropriate wiring diagram in WIRING DIAGRAMS article in the ENGINE PERFORMANCE Section for power terminal identification. If power is not available to power terminals of ECM, check for opens in power circuits. If power is available to ECM power terminals, check for poor ECM ground circuits, or replace faulty ECM.
3. If engine starts and SERVICE ENGINE SOON light does not illuminate, turn ignition off. Disconnect ECM connectors. Turn ignition on and jumper ECM SERVICE ENGINE SOON light driver terminal to ground using a test light. See appropriate wiring diagram in WIRING DIAGRAMS article in the ENGINE PERFORMANCE Section for power terminal identification.
4. If light is now on, repair light driver terminal connections at ECM or replace faulty ECM. If light 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 ECM and bulb, driver circuit shorted to voltage, or an open in the ignition feed to the SERVICE ENGINE SOON light.

A2, SERVICE ENGINE SOON LIGHT ON OR WON'T FLASH CODE 12

1. Turn ignition off. Disconnect ECM connectors. Turn ignition on. If SERVICE ENGINE SOON light is on, check for short to ground in light driver circuit between light and ECM driver terminal. See appropriate wiring diagram in WIRING DIAGRAMS article in the ENGINE PERFORMANCE Section for terminal identification.
2. If light is off with ECM connectors disconnected, turn ignition off. Reconnect ECM connectors. Turn ignition on with engine off. Using a DVOM, check voltage at ALDL test terminal "B". (Scheme 31) If voltage is greater than 9 volts, check for a short to voltage on ALDL terminal "B" wire between ECM and ALDL connector. If voltage is 5-6 volts, proceed to next step. If voltage is less than 5 volts, backprobe appropriate ECM terminal with DVOM. See appropriate wiring diagram in WIRING DIAGRAMS article in the ENGINE PERFORMANCE Section. If 5-6 volts is now present, repair open or short in wire between ECM and ALDL terminal "B".
3. If voltage at terminal "B" of ALDL connector is 5-6 volts, jumper that wire terminal at ECM to ground. If SERVICE ENGINE SOON light flashes a Code 12, and terminal "A" of ALDL was used when grounding terminal "B" the first time, check for open between ALDL connector terminal "A" and ground. If SERVICE ENGINE SOON light does not flash when ECM end of terminal "B" wire is jumpered to ground, check PROM/MEM-CAL for proper installation. If installed correctly, replace ECM, using original PROM/MEM-CAL. Repeat diagnostic circuit check. If Code 12 still does not flash, replace PROM/MEM-CAL. Replace PROM/MEM-CAL only after replacing ECM, as PROM/MEM-CAL is not likely to be at fault.

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 TESTS W/O CODES article in the ENGINE PERFORMANCE Section for diagnosis by symptom (i.e., ROUGH IDLE, NO-START, etc.) or intermittent diagnostic procedures.