Engine Controls - Basic Testing Buick Century V

INTRODUCTION

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

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

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

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

GENERAL MOTORS A & C CHART REFERENCE

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

VISUAL INSPECTION

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

Compression

Check engine mechanical condition with a compression gauge, vacuum gauge, or an engine analyzer. See engine analyzer manual for specific instructions. For compression specifications, refer to 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 Oxygen Sensor Remove oxygen sensor. Install backpressure tester in place of oxygen sensor. After test is completed, coat oxygen sensor threads with anti-seize compound.

Diagnosis

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

PCM REPLACEMENT CHECK

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

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

Flowchart. Scheme 129

NO START DIAGNOSIS (A-3)

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

Definition

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

NO START - ENGINE CRANKS OKAY (2.2L MFI W/ DIS)

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

General Inspection

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

Ignition System

1. Install scan tester. Check for stored PCM trouble codes. If Code 19 is present, diagnose code first. Scan TP sensor voltage. TP sensor reading should be less than 1.0 volt. If reading is not as specified, use Code 21 chart. Scan CTS temperature. Coolant temperature should be close to ambient temperature. If not, use Code 14 or 15 chart. See appropriate TESTS W/CODES article in the ENGINE PERFORMANCE section below. G - TESTS W/CODES - 3.1L G - TESTS W/CODES - 2.2L
2. Scan 7X reference pulses while cranking engine. If reference pulses are not present go to step 11). Crank engine and check for spark using Spark Tester (ST-125) on spark plug wires No. 1 or 4 and 2 or 3. Check one wire at a time. Ground companion spark plug wire and leave other wires connected to spark plugs while cranking. If spark is not present on either wires or spark is present on only one spark plug wire, go to step 6).
3. 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.
4. Disconnect all injector connectors. Connect injector test light to injector No. 1 or 4 connector. Crank engine. Connect injector test light to injector No. 2 or 3 connector. Crank engine. Test light should flash on both tests. If test light flashed, perform injector balance test. See INJECTOR BALANCE TEST in appropriate I - SYS/COMP TESTS article in the ENGINE PERFORMANCE section below. If test light did not flash on both tests, or flashed only on one of the tests, or was on steady on one or both tests, go to step 17). I - SYSTEM/COMPONENT TESTS - 3.1L I - SYSTEM/COMPONENT TESTS - 2.2L
5. Install fuel pressure gauge. Turn ignition on and note fuel pressure after 2 seconds. Pressure should be 41-47 psi (2.9-3.3 kg/cm 2 ). If fuel pressure is okay, check for fouled spark plugs, EGR stuck open or shorted A/C pressure sensor. If fuel pressure is not as specified, diagnose fuel system. CAUTION: When probing DIS circuits, ensure hands and clothing do not contact rotating engine belts and pulleys.
6. Turn ignition off. Disconnect 6-wire Ignition Control Module (ICM) connector. Connect DVOM negative lead to ground and positive lead to ICM terminal "D" (Black wire). Crank engine. Repeat test on ICM terminal "E" (White wire). (Scheme 130) Frequency reading should be 1-10 Hertz. If neither terminals showed frequency response, go to step 8). If only one terminal showed frequency response, diagnose ignition system for misfire. If both terminals showed frequency response, go to next step.
7. Disconnect ICM 2-wire connector. Turn ignition on. Check voltage in ICM connectors "A" (Black wire) and "B" (Pink Wire). (Scheme 130) Battery voltage should be present. If voltage was not present, check for open in circuit. If battery voltage was present, check ICM connector terminals. If terminals are okay, replace ICM.
8. Turn ignition off. Connect test light to battery voltage. Using test light, probe ICM connector terminals "D" (Black wire) and "E" (White wire). Test light should be off. If test light illuminated, go to next step. If test light did not illuminate, disconnect Pink PCM connector. Probe ICM terminals "D" and "E" again. If test light illuminated, repair shorted ICM terminal "A" (Black wire) or "B" (Pink wire) circuit. If test light did not illuminate, replace faulty PCM.
9. Turn ignition on. Using DVOM, check voltage between ground and PCM terminals PB3 and PC15. Voltage should not be present on either terminals. If voltage was not present, go to next step. If voltage was present on either terminals, check for short to voltage in Black or Pink wire between ICM and PCM circuit.
10. Turn ignition off. Connect DVOM between PCM terminals PB3 and PC15. Reading should be infinite resistance. If resistance reading is as specified, inspect Pink PCM connector. If connector is okay, replace PCM. If resistance reading is not as specified, check for short in Black or Pink wire between ICM and PCM circuit.
11. Turn ignition off. Disconnect crankshaft position sensor connector. Connect test light between sensor terminal "C" (Brown wire) and ground. Test light should illuminate. If test light illuminated, go to step 13). If test light did not illuminate, go to next step.
12. Turn ignition off. Using test light, backprobe PCM terminal PD10. If test light illuminated, check sensor circuit for open. If circuit and connector are okay, replace PCM. If test light did not illuminate, disconnect PCM connector. Using DVOM, check sensor feed circuit resistance. Resistance should be infinite. If resistance is infinity, check PCM connections. If okay, replace PCM. If resistance is not infinite, repair short to ground in sensor feed circuit.
13. Turn ignition off. Connect test light to battery positive and probe sensor harness terminal "B" (Red wire). If test light illuminated, go to next step. If test light did not illuminate, check sensor ground circuit for open. If circuit and connection are okay, replace PCM.
14. Turn ignition on. Connect test light to battery positive. Touch and remove test light to sensor harness terminal "A" (Yellow wire). Using Tech 1 scan tester, watch 7X reference. If reference value increases, check sensor connection. If sensor connection is okay, replace crankshaft position sensor. If reference value does not increase, go to next step.
15. Connect test light to ground. Touch test light to sensor harness terminal "A" (Yellow wire). Test light should not illuminate. If test light did not illuminate, check for short to ground or open in sensor reference circuit. If circuit is okay, replace PCM. If test light illuminated, go to next step.
16. Turn ignition off. Disconnect PCM connector. Turn ignition on. Connect test light to PCM terminal PD2 (sensor reference). If test light illuminated, repair short to voltage in sensor reference circuit. If test light did not illuminate, replace PCM.
17. If test light did not flash at both injector harness terminals, go to next step. If test light did not flash at one of injector harness terminals, go to step 20). If test light was on steady on one or both injector harness terminals, check injector drive circuit No. 467 (Dark Blue wire) or 468 (Dark Green) for short to ground. Repair as necessary. If circuit is okay, problem is faulty PCM connection or faulty PCM.
18. Remove injector test light from injector harness. Connect test light to ground and probe injector harness circuit No. 839 (Pink wire) terminal. Turn ignition on. If test light did not illuminate, go to next step. If test light illuminated, check injector driver circuits No. 467 (Dark Blue wire) and No. 468 (Dark Green wire) for open or short to voltage. Repair circuits. If circuits are okay, replace PCM.
19. Disconnect 3-wire injector connector. Connect test light between ground and injector harness circuit No. 839 (Pink wire). Test light should illuminate. If test light illuminated, check for open in harness connector between PCM and injector. If test light did not illuminate, repair open in ignition circuit or in 3-wire injector harness connector.
20. Check injector harness circuit No. 467 (Dark Blue) or No. 468 (Dark Green), which did not illuminate, for open or poor connection to PCM. Repair open circuit. If circuit is okay, check PCM Pink connector. If connector is okay, replace PCM.

Scheme 130

NO START - ENGINE CRANKS OKAY (3.1L MFI 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 (3.1L)

1. Disconnect tachometer wire (if equipped). A shorted tachometer or tachometer circuit will prevent vehicle from starting.
2. Install scan tester. Check for stored PCM trouble codes. Scan TP sensor voltage. If TP sensor reading is greater than 2.5 volts, use Code P0123 chart first. Scan 3X signal 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 1-5) 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. (Scheme 131) If RPM is indicated on scan tester, problem is faulty ignition module harness connection or faulty ignition control module. If RPM is not indicated, problem is open or short to ground in RPM reference circuit or faulty PCM.
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 control module is faulty.
5. Turn ignition off. Install fuel pressure gauge. Turn ignition on. Fuel pressure should be 41-47 psi (2.9-3.3 kg/cm 2 ). If fuel pressure is not as specified, diagnose fuel system. If fuel pressure is okay, disconnect 10-pin injector harness connector. Turn ignition on, engine off. Using a test light connected to ground, probe test light on injector harness circuit No. 839 (Pink wire). (Scheme 131)
6. If test light did not illuminate, check for open in circuit No. 839 (Pink wire). If test light illuminated, install DVOM. Set DVOM in 1 k/ohm position and connect DVOM positive probe on injector harness terminal "D" (Pink wire) and touch DVOM negative probe to injector harness terminals "A", "B", "C", "H", "J" and "K". (Scheme 131) Resistance should be 10-20 ohms.
7. If resistance is not as specified, check injector harness circuit. If circuit is okay, replace faulty injector. If resistance is as specified, set DVOM in DC volts position. With DVOM positive probe connected to battery voltage, probe injector harness terminals "A", "B", "C", "H", "J" and "K" while cranking engine. DVOM should read/toggle from zero to 12 volts on each terminal.
8. If reading is as specified, problem is not present at this point. If reading is not as specified, check for open injector circuit, faulty PCM connections or faulty PCM.
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 came on, go to step 11). If test light did not come on, probe terminal "B" of harness connector with test light connected to ground. (Scheme 131)
10. If test light did not come on, repair open in ignition module power feed circuit (circuit No. 839). If test light came on, repair open in ignition module ground circuit wire (circuit No. 550) between terminal "A" and engine ground. (Scheme 131)
11. Disconnect crankshaft sensor 3-wire connector at ignition module. Using ohmmeter, set ohmmeter to 2 k/ohm position. Check resistance between crankshaft sensor harness terminals "A" and "B". (Scheme 131) 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 crankshaft sensor circuit or replace faulty crankshaft sensor.
12. Set voltmeter on 2-volt AC position. Crank engine with voltmeter leads connected between crankshaft sensor terminals. 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 ignition control module.

Scheme 131

BASIC FUEL SYSTEM CHECKS (A-7)

Fuel Pressure Relief (MFI)

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. 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 2.2L, install Fuel Pressure Gauge (J -34730-1) on fuel pressure connector of fuel rail. On 2.2L, install 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 (MFI)

1. Relieve fuel pressure as previously described in FUEL PRESSURE RELIEF (MFI). On all models except 2.2L, connect Fuel Pressure Gauge (J-34730-1) to fuel pressure fitting on fuel rail. On 2.2L, install Fuel Pressure Gauge (J-29658-D) using Adapter Kit (J-29658-100). This kit modifies fuel pressure gauge so it may be installed in fuel delivery line with quick-disconnect fittings. With gauge installed, turn ignition on and engine off, fuel pressure should read within specification. See FUEL PRESSURE (MFI) table. If no fuel pressure is present, go to step 5).
2. Start engine. Pressure should drop 3-10 psi (.2-.7 kg/cm 2 ). Turn ignition off. Pressure should hold. If pressure does not hold, check for leaking injectors or fittings. If injectors or fittings are not leaking, replace pressure regulator.
3. If pressure is present but less than specification, check for restricted delivery line or fuel filter. Repair as necessary. If no restriction is evident, apply battery voltage to fuel pump test connector using a 10-amp fused jumper wire. For location of fuel pump test connector, see COMPONENT LOCATIONS in appropriate I - SYS/COMP TESTS article in the ENGINE PERFORMANCE section below. I - SYSTEM/COMPONENT TESTS - 3.1L I - SYSTEM/COMPONENT TESTS - 2.2L
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 appropriate I - SYS/COMP TESTS article in the ENGINE PERFORMANCE section below. 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. I - SYSTEM/COMPONENT TESTS - 3.1L I - SYSTEM/COMPONENT TESTS - 2.2L
6. If fuel pressure is present with voltage applied to test connector, test fuel pump relay and voltage supply to relay. See appropriate I - SYS/COMP TESTS article in the ENGINE PERFORMANCE section listed above.

FUEL PRESSURE (MFI)

Fuel Pump Relay

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

1. I - SYSTEM/COMPONENT TESTS - 3.1L
2. I - SYSTEM/COMPONENT TESTS - 2.2L

Fuel Pump Relay By-Pass Procedure

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

FIELD SERVICE MODE CHECK

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

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

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

1. Start engine. With engine running, ground DLC terminal "B". (Scheme 132) In "closed loop" mode, Malfunction Indicator Light (MIL) will flash once a second.
2. In "open loop", MIL will flash 2.5 times a second. If MIL is off most of the time, a lean exhaust is indicated. If MIL is on most of the time, a rich exhaust is indicated.

DATA LINK CONNECTOR (DLC) TEST TERMINALS

Scheme 132

HEI-EST DISTRIBUTOR

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

Spark

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

Ignition Coil Power Source

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

Ignition Coil Resistance

1. Turn ignition off. Remove distributor cap and coil assembly. Invert cap. (Scheme 133) 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 133

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 PCM terminal with engine cranking.
2. A tach pulse signal may be simulated (to test PCM response) by connecting a test light in series between battery and circuit No. 430 PCM terminal. Each time test light is touched to and removed from circuit No. 430, PCM will see this as a tach signal. For circuit and terminal reference, see appropriate schematic under NO START - ENGINE CRANKS OKAY.

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

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

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.

Crankshaft Sensor Pick-Up Coil Short & Resistance Checks

1. Set DVOM on 2000-ohm scale position. Connect DVOM leads to crank angle sensor connector, located on side of engine block. Turn ignition off. Disconnect ignition module connectors. On 2.0L, disconnect PCM connectors. Measure resistance between crankshaft sensor terminals at ignition module connector.
2. Crankshaft sensor resistance should be within specification range listed in CRANKSHAFT SENSOR RESISTANCE table. If resistance is not as specified, replace sensor. If sensor is within specification, go to next step.
3. With sensor installed in block, connect one ohmmeter lead to either sensor terminal at ignition module (PCM 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 DLC. RPM should be indicated on tester when engine is cranked or running. Tach pulse (RPM reference) will be indicated as a voltage signal when a DVOM (with a minimum 10-megohm input impedance) is used to backprobe RPM "high reference" circuit. For circuit and terminal reference, see appropriate schematic in NO START - ENGINE CRANKS OKAY.

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

The Diagnostic Circuit Check determines

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

After performing procedures in PRELIMINARY INSPECTION & ADJUSTMENTS, BASIC FUEL SYSTEM CHECKS and BASIC IGNITION SYSTEM CHECKS, this is the starting point for utilizing the self-diagnostic system for determining computer-related problems. (Scheme 134)and (Scheme 135). 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 and SCAN TESTER USAGE in appropriate TESTS W/CODES article in the ENGINE PERFORMANCE section below.

1. G - TESTS W/CODES - 3.1L
2. G - TESTS W/CODES - 2.2L NOTE: On vehicles equipped with 16-pin DLC or 12-pin DLC without test terminal "B", use of Tech 1 scan tester is required to perform diagnostic circuit check. See DATA LINK CONNECTOR (DLC) TEST TERMINALS table.

1. Check operation of MIL. Turn ignition on with engine off. MIL should be on steady. If MIL illuminates and stays on steady, go to step 3). If MIL does not illuminate, go to A-1, MIL INOPERATIVE. If MIL flashes, go to step 4).
2. On vehicles equipped with 16-pin DLC or 12-pin DLC without test terminal "B", install Tech 1 scan tester and follow scan tester manufacturer's instructions to proceed with test. If MIL does not come on, go to A-1, MIL INOPERATIVE. If MIL comes on, check for diagnostic trouble codes and diagnose codes using appropriate TESTS W/CODES article in the ENGINE PERFORMANCE section below. On vehicles equipped with 12-pin DLC with test terminal "B", go to next step. G - TESTS W/CODES - 3.1L G - TESTS W/CODES - 2.2L
3. Grounding DLC terminal "B" at this time should cause MIL to flash a Code 12, followed by any codes stored in PCM memory. (Scheme 132) MIL going from bright to dim is not considered a code. If MIL dims or remains on and does not flash Code 12, see A-2, MIL ON STEADY OR WON'T FLASH CODE 12. NOTE: On some models, as long as a 30-second pause may occur between code flashes. This is normal and does not indicate necessary component replacement.
4. If MIL begins to flash as soon as ignition is turned on, check for a short to ground on the diagnostic test terminal wire between DLC terminal "B" and PCM terminal No. 5. If circuit is okay, replace PCM.

Scheme 134

Diagnostic Circuit Check & Work Flow. Scheme 135

A-1, MIL INOPERATIVE

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

A-2, MIL ON STEADY OR WON'T FLASH CODE 12

Note. A-2 diagnostic information is not used on 3.1L (VIN M) engine.

2.2L

1. Install Tech 1 scan tester. Turn ignition on with engine off. MIL should come on. If MIL is off, refer to A-1, MIL INOPERATIVE. If MIL is on, check if scan tester is displaying scan data. If scan data is displayed, go to next step. If no scan data is displayed, check for open, short to ground or short to voltage in serial data circuit. If circuit is okay, check for faulty EPROM or PCM.
2. Start engine. Using Tech 1 scan tester, command MIL off then on. If MIL does not respond as commanded, go to next step. If MIL responds as commanded, check for trouble codes. Diagnose any trouble code(s) present. Refer to appropriate TESTS W/CODES article in the ENGINE PERFORMANCE section below. If trouble code(s) is not present, system is operating normally. G - TESTS W/CODES - 3.1L G - TESTS W/CODES - 2.2L
3. Turn ignition off. Disconnect PCM connectors. Turn ignition on. MIL should be off. If MIL did not come on, repair short to ground in circuit No. 419 (Brown/White wire). If MIL came on, check EPROM for proper installation. If EPROM is installed properly, replace PCM using original EPROM. Start engine. Using scan tester, command MIL on then off. If MIL responds as commanded, system is now okay. If MIL does not respond as commanded, replace EPROM.

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.

PCM Wiring Diagram (2.2L VIN 4 - 1 Of 2). Scheme 136

PCM Wiring Diagram (2.2L VIN 4 - 2 Of 2). Scheme 137

PCM Wiring Diagram (3.1L VIN M - 1 Of 3). Scheme 138

PCM Wiring Diagram (3.1L VIN M - 2 Of 3). Scheme 139

PCM Wiring Diagram (3.1L VIN M - 3 Of 3). Scheme 140