Engine Control System - System Testing & Engine Component Tests Cadillac Seville V

MODEL IDENTIFICATION

Vehicle model is identified by fourth character of Vehicle Identification Number (VIN). VIN is stamped on metal pad on top of left end of instrument panel, near windshield. See MODEL IDENTIFICATION table.

MODEL IDENTIFICATION

INTRODUCTION

Before testing separate components or systems, perform all procedures listed in appropriate BASIC DIAGNOSTIC PROCEDURES article. Since many computer-controlled and monitored components will set a DTC if they malfunction, it is also recommended self-diagnostics be performed. See appropriate SELF-DIAGNOSTICS article.

Note. Testing individual components does not isolate shorts or opens. Perform all voltage tests with a DVOM with a minimum 10-megohm input impedance, unless stated otherwise in test procedure. Use ohmmeter to isolate wiring harness shorts or opens.

AIR INDUCTION SYSTEMS

Note. Manufacturer does not provide testing procedures for many individual systems and components. For system and component testing not listed, perform related DTC testing procedure. See appropriate SELF-DIAGNOSTICS article.

Note. For location of components, see COMPONENT LOCATIONS .

SUPERCHARGER

For component testing, perform related DTC testing procedure. See appropriate SELF-DIAGNOSTICS article.

MULTI-RAM SYSTEM DIAGNOSIS (3.0L)

Note. Powertrain Control Module (PCM) may also be referred to as Engine Control Module (ECM).

1. Perform powertrain diagnostic system check. See POWERTRAIN DIAGNOSTIC SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. After performing powertrain diagnostic system check, go to next step.
2. Connect scan tool to Data Link connector (DLC). Retrieve DTCs. If DTCs P1112 or P1113 are not set, go to next step. If DTC P1112 or P1113 is set, perform appropriate diagnostic test. See appropriate SELF-DIAGNOSTICS article.
3. Visually inspect system. Check for disconnected or damaged vacuum hoses and/or components. Check linkage between vacuum actuators and valves for binding or interference with hoses. Ensure wiring is routed properly and not damaged. If problem does not exist, go to next step. If problem exists, repair as necessary and go to step 14 .
4. Start engine and observe vacuum actuator linkages for switchover valves. Using scan tool, command each valve on and off. If both valves operate, go to next step. If either valve does not operate, go to step 6 .
5. Turn ignition off. Remove duct from between intake resonance switchover valve and throttle body. Hold throttle plates open to view moveable divider in back of intake manifold. Move actuator linkage by hand and ensure divider moves with linkage. Look down passages in intake resonance switchover valve to view moveable divider between 2 sides of valve. Move actuator linkage by hand to ensure divider moves with linkage. If both valves operate properly, system is okay. If either valve does not operate, go to step 13 .
6. Using scan tool, exit device control. Disconnect manifold vacuum supply hose at solenoid valve while observing actuator linkage. If actuator does not move when vacuum is disconnected, go to next step. If actuator moves when vacuum is disconnected, go to step 10 .
7. Check for vacuum at manifold vacuum supply hose. If vacuum exists, go to next step. If vacuum does not exist, go to step 11 .
8. Disconnect other hose from solenoid valve and connect hoses together using suitable vacuum connector. If actuator linkage does not operate, go to next step. If actuator linkage operates, go to step 10 .
9. Disconnect vacuum hose from actuator. If vacuum exists, go to step 13 . If vacuum does not exist, go to step 12 .
10. Replace solenoid valve. After repairs, go to step 14 .
11. Repair vacuum supply hose or plugged vacuum source. After repairs, go to step 14 .
12. Repair vacuum hose to actuator. After repairs, go to step 14 .
13. Replace valve/actuator assembly. After repairs, go to next step.
14. Start engine. Observe vacuum actuator linkages for switchover valves. Using scan tool, command each valve on and off. If both valves operate, system is okay. If either valve does not operate, go to step 2 .

COMPUTERIZED ENGINE CONTROLS

Note. For location of components, see COMPONENT LOCATIONS .

PCM POWER & GROUND CHECK

Note. To identify circuits, see WIRING DIAGRAMS article.

Ground Circuits

1. Using DVOM, check for continuity to ground at PCM ground terminals. (Scheme 30) See WIRING DIAGRAMS article. Resistance should be zero ohms. If resistance is not zero ohms, repair open in ground circuit.
2. Connect negative lead of DVOM to a known-good ground. Backprobe positive lead of voltmeter to each PCM ground terminal. With vehicle running, DVOM should indicate less than one volt. If DVOM reading is greater than one volt, check for open, short to voltage, corrosion or loose connection in ground circuit.

Power Circuits

1. Using DVOM, check for battery voltage between PCM continuous power terminal(s) and ground. (Scheme 30) See WIRING DIAGRAMS article. If battery voltage is not present, check for open fuse or fusible link. If fuse or fusible link is okay, check for open in circuit between PCM continuous power terminal and power source.
2. Turn ignition switch to RUN position. Using DVOM, check for battery voltage between PCM ignition power terminals and ground. If battery voltage is not present, check IGN fuse. If fuse is okay, check for open in circuit between battery and ignition switch, and between ignition switch and PCM ignition power terminal. If circuits are okay, check for defective ignition switch.
3. Connect DVOM between ground and PCM starter (crank) signal terminal. On vehicles with manual transmission/transaxle, depress clutch pedal. On vehicles with automatic transmission/transaxle, place gearshift lever in Park. On all vehicles, turn ignition switch to START position. Battery voltage should be present only when ignition switch is in START position.
4. If voltage is not present, check CRANK fuse or fusible link between ignition switch and PCM starter (crank) signal terminal. If fuse or fusible link is okay, check for open in circuit between ignition switch and PCM starter (crank) signal terminal, or check for defective ignition switch.

PCM Harness Resistance

Turn ignition switch to LOCK position. Disconnect PCM and related component harness connectors. Check for open or short circuits between PCM harness connector terminal and component harness connector terminal. (Scheme 30) See WIRING DIAGRAMS article. If harness is open or shorted, repair as necessary.

Scheme 30

Scheme 31

Scheme 32

Scheme 33

Scheme 34

SL Models

PCM CONNECTOR J1 TERMINAL IDENTIFICATION (1.9L)

PCM CONNECTOR J2 TERMINAL IDENTIFICATION (1.9L)

ENGINE SENSORS & SWITCHES

Note. For additional sensor testing specifications, see appropriate SENSOR OPERATING RANGE CHARTS article.

Note. Perform powertrain diagnostic system check prior to testing, and after completing any repairs. See POWERTRAIN DIAGNOSTIC SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article.

Manufacturer does not provide testing procedures for many individual systems and components. For sensor and switch testing not listed, perform related DTC testing procedure. See appropriate SELF-DIAGNOSTICS article.

Note. For location of components, see COMPONENT LOCATIONS .

2.2L (Cavalier & Sunfire) & 2.4L

Perform related DTC testing procedure. See appropriate SELF-DIAGNOSTICS article.

3.1L (Lumina)

1. Perform powertrain diagnostic system check. See POWERTRAIN DIAGNOSTIC SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. After performing powertrain diagnostic system check, go to next step.
2. Check for the following conditions: MAP sensor seal damaged or missing. Vacuum hoses disconnected, damaged or incorrectly routed. Intake manifold vacuum leaks. Vacuum leak at throttle body. Vacuum leaks in EGR system. Faulty PCV system. If problem does not exist, go to next step. If problem exists, repair as necessary. After repairs, go to step 14 .
3. Disconnect MAP sensor harness connector. Turn ignition on, engine off. Using scan tool, observe MAP sensor parameter. If scan tool displays zero volts, go to next step. If scan tool does not display zero volts, go to step 12 .
4. Connect a 3-amp fused jumper wire between MAP sensor signal circuit (Light Green wire) and MAP sensor reference voltage circuit (Gray wire) at MAP sensor harness connector. Turn ignition on, engine off. Observe MAP sensor parameter. If scan tool displays 4.95 volts, go to next step. If scan tool does not display 4.95 volts, go to step 8 .
5. Using test light connected to battery voltage, probe MAP sensor signal circuit (Light Green wire) at MAP sensor harness connector. Observe MAP sensor parameter. If scan tool displays 4.95 volts, go to next step. If scan tool does not display 4.95 volts, go to step 9 .
6. Turn ignition off. Check for faulty MAP sensor harness connections. If connections are okay, go to next step. If connections are not okay, repair as necessary. After repairs, go to step 14 .
7. Check for open or high resistance in MAP sensor ground circuit (Orange/Black wire). If ground circuit is okay, go to step 11 . If ground circuit is not okay, repair as necessary. After repairs, go to step 14 .
8. Check for open or high resistance in MAP sensor 5 volt reference circuit (Gray wire). If MAP sensor 5 volt reference circuit is okay, go to step 10 . If MAP sensor 5 volt reference circuit is not okay, repair as necessary. After repairs, go to step 14 .
9. Check for open, short to ground or short to sensor ground circuit (Orange/Black wire) in MAP sensor signal circuit (Light Green wire). If MAP sensor signal circuit is okay, go to next step. If MAP sensor signal circuit is not okay, repair as necessary. After repairs, go to step 14 .
10. Check for poor MAP sensor signal circuit connection at PCM. If connection at PCM is okay, go to next step. If connection at PCM is not okay, repair as necessary. After repairs, go to step 14 .
11. Turn ignition off. Disconnect PCM harness connectors. Turn ignition on. Check for short to voltage in MAP sensor reference voltage circuit (Gray wire). If short to voltage does not exist, go to next step. If short to voltage exists, repair as necessary. After repairs, go to step 14 .
12. Replace MAP sensor. If system is repaired, go to step 14 . If system is not repaired, go to next step.
13. Replace PCM. After repairs, go to next step.
14. Start engine and idle. While observing MAP sensor parameter on scan tool, increase engine RPM. If MAP sensor valve changes, system is okay. If MAP sensor valve does not change, go to step 2 .

3.1L (Except Lumina) 3.4L & 3.8L

1. Perform powertrain diagnostic system check. See POWERTRAIN DIAGNOSTIC SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. After performing powertrain diagnostic system check, go to next step.
2. Install scan tool. Turn ignition on, engine off. Using scan tool, monitor and record MAP sensor kPa. MAP sensor value should be within 3 kPa of BARO. If MAP sensor value is normal for altitude, go to next step. If MAP sensor value is not normal for altitude, go to step 7 .
3. Using scan tool, observe MAP sensor kPa display. Start engine. If MAP sensor value changes, go to next step. If MAP sensor value does not change, go to step 7 .
4. Turn ignition off. Disconnect vacuum source from MAP sensor. Leave MAP sensor connected to engine harness. Connect hand vacuum pump to MAP sensor. Turn ignition on, engine off. Observe MAP sensor kPa and slowly apply vacuum one in. Hg at a time. Each one in. Hg of vacuum should result in 3-4 kPa drop in MAP sensor display. Observe MAP sensor display for skip or jump while increasing vacuum up to 20 in. Hg. If MAP sensor display for skips or jumps, go to step 13 . If MAP sensor display does not skip or jump, go to next step.
5. Observe MAP sensor kPa display with 20 in. Hg of vacuum applied to sensor. If kPa display is less than 34 kPa, go to next step. If kPa display is 34 kPa or more, go to step 7 .
6. Disconnect hand held vacuum pump. If MAP sensor display returns to value specified in step 2 , system is okay. If MAP sensor display does not return to value specified in step 2), go to step 13 .
7. Turn ignition off. Disconnect MAP sensor harness connector. Turn ignition on, engine off. Using scan tool, observe MAP sensor voltage display. If more than zero volts exist, go to step 10 . If more than zero volts does not exist, go to step 8 .
8. Using fused jumper wire, jumper MAP sensor 5-volt reference circuit (Gray wire) to MAP sensor signal circuit (Light Green wire). Using scan tool, observe MAP sensor voltage display. If MAP sensor voltage is 4.7-5.2 volts, go to next step. If MAP sensor voltage is not 4.7-5.2 volts, go to step 11 .
9. Remove jumper wire. Using test light connected to battery voltage, probe MAP sensor ground circuit (Orange/Black wire). If test light illuminates, go to step 13 . If test light does not illuminate, go to step 12 .
10. Check MAP sensor signal circuit (Light Green wire) for short to voltage. Repair as necessary. After repairs, go to step 2 . If circuit is okay, go to step 15 .
11. Check MAP sensor 5-volt reference signal circuit (Gray wire) for high resistance. Repair as necessary. After repairs, go to step 2 . If circuit is okay, go to step 15 .
12. Check MAP sensor ground circuit (Orange/Black wire) for high resistance. Repair as necessary. After repairs, go to step 2 . If circuit is okay, go to step 15 .
13. Check MAP sensor connector for poor connection or terminal contact. Repair as necessary. After repairs, go to step 2 . If circuit is okay, go to next step.
14. Replace MAP sensor. After repairs, go to step 2 .
15. Inspect PCM for poor connection or terminal contact. Repair as necessary. After repairs, go to step 2 . If PCM connections are okay, go to next step.
16. Replace PCM. After repairs, go to step 2 .

PARK NEUTRAL POSITION SWITCH

See appropriate ELECTRONIC CONTROLS article in AUTOMATIC TRANSMISSIONS for testing procedures.

MOTORS, RELAYS & SOLENOIDS

Note. Manufacturer does not provide testing procedures for many individual systems and components. For module, motor, relay and solenoid testing not listed, perform related DTC testing procedure. See appropriate SELF-DIAGNOSTICS article.

Note. For location of components, see COMPONENT LOCATIONS .

Idle Air Control (IAC) Motor

See IDLE CONTROL SYSTEM .

A/C Compressor Clutch Relay

See appropriate MANUAL A/C-HEATER SYSTEMS or AUTOMATIC A/C-HEATER SYSTEMS article in AIR CONDITIONING & HEATING.

Fuel Pump Relay

Fuel pump relay is located in underhood fuse/relay block. To test fuel pump relay, see FUEL PUMP ELECTRICAL CIRCUIT under appropriate NO START - ENGINE CRANKS OKAY in appropriate BASIC DIAGNOSTIC PROCEDURES article.

SOLENOIDS

Note. Perform related DTC testing procedure. See appropriate SELF-DIAGNOSTICS article.

FUEL SYSTEMS (GASOLINE)

Manufacturer does not provide testing procedures for many individual systems and components. For fuel system testing not listed, perform related DTC testing procedure. See appropriate SELF-DIAGNOSTICS article.

Note. Perform powertrain diagnostic system check prior to testing, and after completing any repairs. See POWERTRAIN DIAGNOSTIC SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article.

Note. For location of components, see COMPONENT LOCATIONS .

FUEL DELIVERY

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

Fuel Pump Circuit

See FUEL PRESSURE under FUEL SYSTEMS in appropriate BASIC DIAGNOSTIC PROCEDURES article.

Fuel Pressure Regulator

See FUEL PRESSURE under FUEL SYSTEMS in appropriate BASIC DIAGNOSTIC PROCEDURES article.

FUEL CONTROL

Note. Retrieve DTCs and perform appropriate DTC test before performing FUEL INJECTOR CIRCUIT DIAGNOSIS. See appropriate SELF-DIAGNOSTICS article. Also, ensure all mechanical and ignition coil/module circuit malfunctions are repaired before performing fuel injector circuit diagnosis.

Fuel Injector Balance Test

Note. Allow engine to cool down to avoid irregular readings due to "hot soak" fuel boiling. To prevent flooding, the fuel injector balance test should not be performed more than once without starting and running engine.

Note. If injectors are dirty, they should be cleaned using approved injector cleaning procedure before performing fuel injector balance test.

1. If fuel injector coil test has been performed, go to next step. If fuel injector coil test has not been performed, perform fuel injector coil test. See «FUEL INJECTOR COIL TEST»(/cadillac/seville/v-1998-2004/remont/testing-diagnostics/#engine-control-system-system-testing-engine-component-tests__fuel-injector-coil-test) .
2. If engine coolant temperature is less than 201°F (94°C), go to step 4 . If engine coolant temperature is greater than 201°F (94°C), go to next step.
3. Allow engine to cool until coolant temperature is less than 201°F (94°C), then go to next step.
4. Install fuel pressure gauge. Turn ignition on, and then off. Bleed air from fuel pressure gauge. Using scan tool, energize fuel pump. Observe fuel pressure gauge reading. See appropriate FUEL PUMP PRESSURE SPECIFICATIONS table. If fuel pressure reading is within specification, go to next step. If fuel pressure reading is not within specification, perform fuel system diagnosis. See appropriate BASIC DIAGNOSTIC PROCEDURES article.
5. Turn fuel pump off. Observe fuel pressure gauge. If fuel pressure remains constant, go to next step. If fuel system does not remain constant, perform fuel system diagnosis. See appropriate BASIC DIAGNOSTIC PROCEDURES article.
6. Disconnect fuel injectors harness connector. Using appropriate fuel injector adapter, connect Fuel Injector Tester (J-39021) to fuel injector. Connect fuel injector tester power leads to appropriate battery terminals. Set amperage supply selector switch on fuel injector tester to Balance Test 2.5-amp position. Turn ignition on, and then off. Record fuel pressure reading (first reading). Energize injector by depressing PUSH TO START TEST button on injector tester and hold until fuel pressure gauge stabilizes. Record fuel pressure reading (second reading). Subtract first reading from second reading (this result is pressure drop value). Add pressure drop value for each injector together and divide total by total number of injectors. If any injector's drop value is greater or less than average drop value by 1.5 psi, replace faulty injector(s) as necessary. If no injector's drop value is greater or less than average drop value by 1.5 psi, repair by symptom. See appropriate TROUBLE SHOOTING - NO CODES article.

FUEL PRESSURE SPECIFICATIONS (EXCEPT SATURN)

FUEL PRESSURE SPECIFICATIONS (SATURN)

Fuel Injector Coil Test

1. Perform powertrain diagnostic system check. See appropriate POWERTRAIN DIAGNOSTIC SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article.
2. Using scan tool, check engine coolant temperature. If scan tool displays 50-90°F (10-32°C), go to next step. If scan tool does not display 50-90°F (10-32°C), go to step 4 .
3. Disconnect fuel injector connector. Using DVOM, measure resistance of each fuel injector. Resistance for all injectors should be 11-14 ohms. If resistance is not as specified, go to step 6 . If resistance is as specified, see «INJECTOR COIL TEST DIAGNOSTIC AIDS»(/cadillac/seville/v-1998-2004/remont/testing-diagnostics/#engine-control-system-system-testing-engine-component-tests__injector-coil-test-diagnostic-aids) .
4. Disconnect fuel injector multi-way connector. Using DVOM, measure resistance of each fuel injector. Record each fuel injector value. Subtract lowest resistance value from highest resistance value. If difference is equal to, or less than, 3 ohms, see «INJECTOR COIL TEST DIAGNOSTIC AIDS»(/cadillac/seville/v-1998-2004/remont/testing-diagnostics/#engine-control-system-system-testing-engine-component-tests__injector-coil-test-diagnostic-aids) . If resistance difference is not as specified, go to next step.
5. Add all fuel injector resistance values, to obtain total resistance value. Divide total resistance value by number of fuel injectors, to obtain average resistance value. Subtract lowest and highest individual fuel injector resistance values from average resistance value. Replace fuel injector with greatest resistance difference, above or below average. Repair as necessary. After repairs, go to step 7 .
6. If resistance of fuel injector(s) is not 11-14 ohms, replace fuel injector(s). After repairs, go to next step.
7. Operate system in order to verify repair. If system does not operate properly, go to step 2 .

Injector Coil Test Diagnostic Aids

Monitoring misfire current counters, or misfire graph, may help isolate fuel injector causing condition.

Operating vehicle over a wide temperature range may help isolate fuel injector causing condition.

Perform fuel injector coil test within conditions of customers concern. A fuel injector condition may only be apparent at a certain temperature, or under certain conditions. If fuel injector coil test does not isolate condition perform fuel injector balance test. See FUEL INJECTOR BALANCE TEST .

Injector Leak Test (1.9L)

1. Disconnect negative battery terminal. Remove air intake tube and resonator. Install Fuel Gauge Bar Kit (SA9127E) to fuel pressure test port. Bleed system pressure through bleed hose.
2. Disconnect fuel pressure regulator vacuum hose. Remove fuel lines from bracket, leaving fuel supply lines attached to fuel rail assembly and connectors. Disconnect and plug fuel return line from fuel rail.
3. Remove fuel rail assembly retaining bolts. Pull fuel rail back far enough that injector nozzles are visible but still in intake ports. Secure fuel rail to intake manifold with wire.
4. Wipe off any fuel or debris from fuel injector tips. Place a clean, White towel directly under fuel injectors, with towel lightly touching each fuel injector tip to easily spot a leaky injector.
5. Reconnect negative battery terminal. Ensure battery is fully charged. Cycle ignition on and off several times. DO NOT start engine. Observe fuel injector tips for 5 minutes. Fuel rail pressure should be about 46 psi (3.23 kg/cm 2 ) with fuel rail return line plugged. Run test at least twice. Replace any leaky fuel injector.
6. Bleed fuel pressure through bleed hose and remove fuel pressure gauge. Reinstall fuel rail, fuel return line and pressure regulator vacuum hose. Lubricate injector "O" rings and male end of steel line with clean engine oil prior to installation. Start engine and check for fuel leaks.

Fuel Pump Relay (Gasoline)

See RELAYS under MOTORS, RELAYS & SOLENOIDS.

FUEL SYSTEMS (2.2L - CAVALIER CNG)

Note. For location of components, see COMPONENT LOCATIONS .

Description

Lock-off relay is energized whenever Powertrain Control Module (PCM) supplies power to gasoline fuel pump circuit. PCM supplies power to gasoline fuel pump circuit for approximately 2 seconds at every ignition on cycle and whenever 7X reference pulses indicate engine is cranking or running. When energized, lock-off relay supplies power to high and low pressure lock-off solenoids. At initial ignition on cycle, PCM energizes gasoline fuel pump relay, supplying power to fuel pump power circuit for a two second prime pulse. When prime pulse is supplied to fuel pump power circuit, lock-off relay is energized.

When engine is started, PCM energizes gasoline fuel pump relay, supplying power to fuel pump power circuit. PCM will supply power to fuel pump power circuit, regardless of fuel system that in operation, as long as crankshaft pulses are monitored (engine is running).

High and Low Pressure Lock-Off (HPL and LPL) solenoids are energized by Alternate Fuel Engine Control Unit (AF ECU) when vehicle is operating in CNG mode. At initial ignition on request, AF ECU will close the HPL solenoid control circuit driver (completing circuit path to ground) for a one second CNG prime pulse. Prime pulse occurs at same time as gasoline fuel pump prime pulse occurs. This ensures lock-off relay will be energized and supplying power to lock-off solenoids at the same time AF ECU closes driver and supplies ground path. When engine is cranking or running, AF ECU closes BOTH lock-off solenoid control circuit drivers, allowing engine to operate on CNG.

Diagnostic Procedures

1. If powertrain diagnostic system check has been performed, go to next step. If powertrain diagnostic system check has not been performed, go to POWERTRAIN DIAGNOSTIC SYSTEM CHECK (CNG) under SELF-DIAGNOSTIC SYSTEM in appropriate SELF-DIAGNOSTICS - 2.2L & 2.4L "J" & "N" BODIES - GASOLINE & CNG article. After performing powertrain diagnostic system check, go to next step.
2. Turn ignition off. Locate and disconnect LPL solenoid connector. (Scheme 35) Connect test light between LPL solenoid connector terminal "A" (Purple wire) and ground. Attempt to start engine. If test light illuminates while engine is cranking or running, go to next step. If test light does not illuminate while engine is cranking or running, go to step 6.
3. Turn ignition off and wait 30 seconds. Turn ignition on. Using scan tool, clear any DTCs from AF ECU. Connect test light between LPL solenoid connector terminals "A" (Purple wire) and "B" (Light Blue wire). Attempt to start engine. If test light illuminates while engine is cranking or running, go to next step. If test light does not illuminate while engine is cranking or running, go to step 10.
4. Turn ignition off. Remove CNG fuel tank cover from inside trunk. Locate and disconnect HPL solenoid connector. (Scheme 35) Connect test light between HPL solenoid connector terminal "A" (White wire) and ground. Attempt to start engine. If test light illuminates while engine is cranking or running, go to next step. If test light does not illuminate while engine is cranking or running, go to step 11.
5. Turn ignition off and wait 30 seconds. Connect test light between HPL solenoid connector terminals "A" (White wire) and "B" (Light Green wire). Turn ignition on. If test light illuminates when ignition is turned on, go to step 20. If test light does not illuminate when ignition is turned on, go to step 10.
6. Ensure engine is idling or cranking. Using a test light connected to ground, backprobe lock-off relay connector terminal No. 87 (Purple wire). Lock-off relay is located behind left front fascia, below headlight (18). (Scheme 35) If test light illuminates while engine is running or cranking, go to step 12. If test light does not illuminate while engine is running or cranking, go to next step.
7. Disconnect lock-off relay connector. Ensure engine is idling or cranking. Connect test light between lock-off relay connector terminals No. 85 (Gray wire) and No. 86 (Black wire). If test light illuminates while engine is running or cranking, go to next step. If test light does not illuminate while engine is running or cranking, go to step 9.
8. Ensure engine is idling or cranking. Connect test light between ground and lock-off relay connector terminal No. 30 (Orange wire). If test light illuminates while engine is running or cranking, go to step 16. If test light does not illuminate while engine is running or cranking, go to step 13.
9. Turn ignition off. Connect test light between ground and lock-off relay connector terminal No. 85 (Gray wire). Observe test light. Turn ignition on. Attempt to start engine. If test light illuminates while engine is running or cranking, go to step 14. If test light does not illuminate while engine is running or cranking, go to step 15.
10. Check for open or high resistance in Gray wire between lock-off relay connector terminal No. 85 and splice S004. Check for poor connections at lock-off solenoid and AF ECU. Repair as necessary. After repairs, go to step 20. If circuit and connections are okay, go to step 19.
11. Repair open in Purple wire between splice S005 and connector C454 terminal "A". Purple wire changes to White wire at C454. S005 is located approximately 24" (60 cm) from harness pass-through located below steering column (engine side). Repair open in White wire between connector C454 terminal "A" and HPL solenoid connector terminal "A". After repairs, go to step 20.
12. Repair open in Purple wire between LPL solenoid connector terminal "A" and lock-off relay connector terminal No. 87. After repairs, go to step 20.
13. Repair open in Orange wire between lock-off relay connector terminal No. 30 and splice S001, located approximately 1.5" (3.5 cm) from 4 relay break outs, toward AF ECU connector break outs below left front headlight. After repairs, go to step 20.
14. Repair open in Black wire between lock-off relay connector terminal No. 86 and ground connection located on left side of engine/transmission. After repairs, go to step 20.
15. If test light illuminated for 2 second bulb-check when ignition was first turned on, go to next step. If test light did not illuminate for 2 second bulb-check when ignition was first turned on, go to step 17.
16. Check for open or short in Purple/White wire between Ignition Control Module (ICM) connector C2 terminal "D" and PCM connector C1 terminal No. 8. (Scheme 30)and (Scheme 36). Check for poor connections at PCM and ICM connectors. Repair as necessary. After repairs, go to step 20. If circuit and connections are okay, go to POWERTRAIN DIAGNOSTIC SYSTEM CHECK (CNG) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 2.2L & 2.4L "J" & "N" BODIES - GASOLINE & CNG article.
17. Repair open in Gray wire between lock-off relay connector terminal No. 85 and splice S004. After repairs, go to step 20.
18. Replace lock-off relay. After repairs, go to step 20.
19. Replace AF ECU. See ALTERNATE FUEL ENGINE CONTROL UNIT under COMPUTERIZED ENGINE CONTROLS in REMOVAL, OVERHAUL & INSTALLATION - CARS article. Program (flash) AF ECU with correct vehicle software and calibration. See ALTERNATE FUEL ENGINE CONTROL UNIT under PROGRAMMING in SELF-DIAGNOSTICS - 2.2L & 2.4L "J" & "N" BODIES - GASOLINE & CNG article. After performing repairs and procedures, go to next step.
20. Turn ignition off. Remove all test equipment. Reconnect any disconnected components and/or connectors. Using scan tool, clear DTCs from AF ECU and PCM. Turn ignition off for 30 seconds. Start engine and allow to idle. Start engine and operate vehicle noting operation of Fuel Indicator Light (FIL) and Malfunction Indicator Light (MIL). Observe vehicle performance and driveability in gasoline and alternate fuel modes. If FIL or MIL do not illuminate and vehicle performs normally, system is okay at this time. If FIL or MIL illuminate or vehicle does not performs normally, go to POWERTRAIN DIAGNOSTIC SYSTEM CHECK (CNG) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 2.2L & 2.4L "J" & "N" BODIES - GASOLINE & CNG article.

Scheme 35

Scheme 36

Alternate Fuel Engine Control Unit (AF ECU) supplies power to AF fuel pump relay coil when engine starts and runs on CNG. AF fuel pump relay allows AF ECU to turn off gasoline fuel pump and supply a voltage source for lock-off relay. At initial ignition on, AF fuel pump relay is not energized by AF ECU. Powertrain Control Module (PCM) energizes gasoline fuel pump relay, supplying power to fuel pump power circuit for 2 second prime pulse. When prime pulse is supplied to fuel pump power circuit, lock-off relay is energized and gasoline fuel pump receives 2 second prime pulse power. When the engine is started, PCM energizes gasoline fuel pump relay, supplying power to fuel pump power circuit. When engine is operating on CNG, AF ECU energizes AF fuel pump relay, turning off the gasoline fuel pump. Lock-off relay continues to be energized by gasoline fuel pump relay.

1. If alternative fuels engine controls diagnostic system check has been performed, go to next step. If alternative fuels engine controls diagnostic system check has not been performed, go to POWERTRAIN DIAGNOSTIC SYSTEM CHECK (CNG) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 2.2L & 2.4L "J" & "N" BODIES - GASOLINE & CNG article. After performing alternative fuels engine controls diagnostic system check, go to next step.
2. Ensure both alternate fuel and gasoline fuel systems have 1/4 tank of fuel. Add fuel to ensure this criteria is reached. If CNG 20-amp fuse has been removed, replace fuse in underhood fuse block. (Scheme 37) Crank and attempt to start engine. If engine starts and runs at all, go to step 4. If engine does not start and run at all, go to next step.
3. Turn ignition off and wait 30 seconds. Disconnect Black fuel pump connector C019 located at top left of engine (26). (Scheme 35) Connect test light between ground and relay side of fuel pump connector C019 terminal "A" (Gray wire). Turn ignition on. If test light illuminates for 2 seconds and turns off, go to step 14. If test light does not illuminate for 2 seconds or does not turn off, go to step 13.
4. If vehicle operates on CNG but not gasoline, go to next step. If does not operate on CNG or gasoline, or only operates on gasoline, go to POWERTRAIN DIAGNOSTIC SYSTEM CHECK (CNG) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 2.2L & 2.4L "J" & "N" BODIES - GASOLINE & CNG article.
5. Turn ignition off and wait 30 seconds. Locate AF fuel pump relay. (Scheme 35) Using a test light connected to ground, backprobe AF fuel pump relay connector terminal No. 30 (Gray wire). Turn ignition on. If test light illuminates for 2 seconds and turns off, go to next step. If test light does not illuminate for 2 seconds or does not turn off, go to step 16.
6. Start engine and allow to idle. Ensure vehicle is operating on CNG. Using a test light connected to ground, backprobe AF fuel pump relay connector terminal 87A (Gray/Black wire). If test light illuminates, go to step 8. If test light does not illuminate, go to next step.
7. Using scan tool, attempt to communicate with AF ECU. With test light still connected, command AF fuel pump relay on and off. If test light illuminates when AF fuel pump relay is commanded off, go to step 10. If test light does not illuminate when AF fuel pump relay is commanded off, go to step 17.
8. Ensure engine is idling. Using a test light connected to battery voltage, backprobe AF fuel pump relay connector terminal No. 85 (Black wire). If test light illuminates, go to next step. If test light does not illuminate, go to step 18.
9. Ensure engine is idling. Using a test light connected to ground, backprobe AF fuel pump relay connector terminal No. 86 (Brown wire). If test light illuminates, go to step 21. If test light does not illuminate, go to step 19.
10. Ensure ignition is off. Remove CNG fuse (20-amp) from underhood fuse block to force a switchover to gasoline operation. Crank engine. If engine starts and runs on gasoline, go to step 23. If engine does not start and run on gasoline, go to next step.
11. Turn ignition off and wait 30 seconds. Disconnect Black fuel pump connector C019 located at top left of engine (26). (Scheme 35) Connect jumper wire between underhood relay side of AF fuel pump connector terminals "A" (Gray wire) and "B" (Gray wire). Crank engine. If engine starts and runs on gasoline, go to step 20. If engine does not start and run on gasoline, go to next step.
12. A failure exists in gasoline fuel pump circuit between gasoline fuel pump and connector C019 or poor ground connection for fuel pump. Diagnose and repair as necessary. After repairs, go to step 23.
13. A failure exists in gasoline fuel pump relay circuit. If a blown gasoline fuel pump fuse is diagnosed, check for short to ground in CNG harness. Diagnose and repair as necessary. After repairs, go to step 23.
14. Monitor test light while cranking engine. If test light illuminates while engine is cranking, go to next step. If test light does not illuminate while engine is cranking, go to NO START - ENGINE CRANKS OKAY (2.2L - CAVALIER & SUNFIRE) under NO-START DIAGNOSIS in BASIC DIAGNOSTIC PROCEDURES - CARS - EXCEPT METRO & PRIZM article.
15. Check for open or poor connections in Gray wire between connector C019 terminal "A" and splice S004. Repair as necessary. After repairs, go to step 23. If circuit is okay, go to POWERTRAIN DIAGNOSTIC SYSTEM CHECK (CNG) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 2.2L & 2.4L "J" & "N" BODIES - GASOLINE & CNG article.
16. Repair open in Gray wire between AF fuel pump relay connector terminal No. 30 and splice S004. After repairs, go to step 23.
17. Check for poor connections at AF fuel pump relay. Check for short to voltage in Brown wire between AF fuel pump relay connector terminal No. 86 and AF ECU Blue connector C001 terminal No. 30. (Scheme 39) Repair as necessary. After repairs, go to step 23. If circuit and connections are okay, go to step 21.
18. Repair open in Black wire between AF fuel pump relay connector terminal No. 85 and splice S006 located approximately 18" (40 cm) from ground connection on left side of engine. After repairs, go to step 23.
19. Check for poor connections at AF fuel pump relay. Using DVOM, check continuity of Brown wire between AF fuel pump relay connector terminal No. 86 and AF ECU Blue connector C001 terminal No. 30. (Scheme 39) Also check for short to ground in Brown wire. Repair as necessary. After repairs, go to step 23. If circuit and connections are okay, go to step 22.
20. Repair open in Gray/Black wire between AF fuel pump relay connector terminal 87A and connector C019 terminal "B". After repairs, go to step 23.
21. Replace AF fuel pump relay. After repairs, go to step 23.
22. Replace AF ECU. See ALTERNATE FUEL ENGINE CONTROL UNIT under COMPUTERIZED ENGINE CONTROLS in REMOVAL, OVERHAUL & INSTALLATION - CARS article. Program (flash) AF ECU with correct vehicle software and calibration. See ALTERNATE FUEL ENGINE CONTROL UNIT under PROGRAMMING in SELF-DIAGNOSTICS - 2.2L & 2.4L "J" & "N" BODIES - GASOLINE & CNG article. After performing repairs and procedures, go to next step.
23. Turn ignition off. Remove all test equipment. Reconnect any disconnected components and/or connectors. Using scan tool, clear DTCs from AF ECU and PCM. Turn ignition off for 30 seconds. Start engine and allow to idle. Start engine and operate vehicle noting operation of Fuel Indicator Light (FIL) and Malfunction Indicator Light (MIL). Observe vehicle performance and driveability in gasoline and alternate fuel modes. If FIL or MIL do not illuminate and vehicle performs normally, system is okay at this time. If FIL or MIL illuminate or vehicle does not performs normally, go to POWERTRAIN DIAGNOSTIC SYSTEM CHECK (CNG) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 2.2L & 2.4L "J" & "N" BODIES - GASOLINE & CNG article.

Scheme 37

Alternative Fuel Engine Control Unit (AF ECU) controls fuel system while vehicle is operating on alternative fuel. AF ECU receives signals from various engine sensors and determines correct amount of fuel required by engine. Full tank can contain fuel at 3600 psi (24,820 kPa). A High Pressure Lock-Off (HPL) solenoid in the tank and Low Pressure Lock-Off (LPL) solenoid in fuel line prevent fuel flow. AF ECU commands the HPL ONLY open for one second at every ignition ON for a CNG prime pulse. CNG prime pulse is performed charge fuel line and allow Fuel Pressure Sensor (FPS) to monitor amount of fuel pressure in tank. AF ECU commands both HPL and LPL open when engine RPM indicates engine is cranking or running on CNG.

This fuel delivery system uses 3 different pressure stages to lower fuel pressure from tank pressure down to a delivery pressure which is slightly above atmospheric pressure.

1. High Pressure (Tank) Stage - When AF ECU commands HPL open, fuel begins to flow through High Pressure Regulator (HPR). HPR reduces fuel pressure to 115-220 psi (793-1517 kPa). Outlet of HPR is intermediate pressure stage.
2. Intermediate Pressure Stage With pressure 115-220 psi (793-1517 kPa), fuel exiting HPR flows through intermediate fuel line to Low Pressure Lock-Off (LPL) solenoid. LPL is controlled by AF ECU. Fuel flows out of LPL through another portion of the intermediate fuel line and into Low Pressure Regulator (LPR). Inlet of LPR is the low pressure stage.
3. Low Pressure Stage Low pressure regulator is a 2 stage regulator. Fuel enters LPR at intermediate stage pressure of 115-220 psi (793-1517 kPa). Primary stage of LPR operation reduces fuel pressure down to 4-6 psi (28-41 kPa). Fuel pressure is then again reduced in the secondary stage of LPR, down to 2-5 in. H 2 0 (5.1-12.7 cm). Fuel exits LPR and flows through low pressure hose and into Gas Mass Sensor/Mixture Control Valve (GMS/MCV).

Diagnostic Procedure

1. Perform powertrain diagnostic system check. See POWERTRAIN DIAGNOSTIC SYSTEM CHECK (CNG) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 2.2L & 2.4L "J" & "N" BODIES - GASOLINE & CNG article. If any DTCs other than P1202 are set, diagnose those DTCs first. See DIAGNOSTIC TROUBLE CODE DEFINITIONS in SELF-DIAGNOSTICS - 2.2L & 2.4L "J" & "N" BODIES - GASOLINE & CNG article. If no DTCs other than P1202 are set, go to next step.
2. Connect vehicle to CNG dispensing equipment and verify that CNG tank is at least 3/4 full. This would be a pressure of 1200 psi (8274 kPa). Add CNG to tank as necessary to bring to proper level. Go to next step. NOTE: During next step, rhythmic pressure fluctuations of 10-20 psi are normal. A defective HPR is not indicated unless fluctuations become excessive.
3. Turn ignition off. Remove dust cap from fuel pressure test port located on fuel line near LPR. (Scheme 38) Using parts included in CNG Electronic Pressure Gauge Set (J 39970), install Fuel Test Port Adaptor (J 39970-100) onto fuel pressure test port. Connect Electronic Fuel Pressure Gauge (J 39970) to adaptor. Connect DVOM to gauge. Observe pressure while cranking engine. If a DTC sets that forces a switch-over to gasoline operation (for example: DTC P1202), fuel pressure can only be monitored before DTC sets. If vehicle will not idle in CNG mode, note pressures during cranking. If possible, start engine and allow to idle until engine reaches operating temperature. Record pressure on DVOM at idle. Observe and record pressure while performing the following procedures: Apply parking brake. Press and firmly hold brake pedal. Place vehicle in Drive. Depress throttle to 80 percent (power brake) for maximum of 10 seconds. Release throttle and allow engine to idle in neutral for a minimum of 2 minutes for transmission to cool. If recorded pressure values are 115-200 psi (793-1517 kPa), go to step 5. If recorded pressure values are not 115-200 psi (793-1517 kPa), go to next step.
4. If recorded pressure was more than 220 psi (1517 kPa), go to step 14. If recorded pressure was not more than 220 psi (1517 kPa), go to step 8.
5. Turn ignition off. Remove LPR primary test port plug. (Scheme 38) Connect pressure gauge adaptor to LPR primary test port. Connect 0-15 PSI Pressure Gauge (J 28552) to adaptor. Observe pressure while cranking engine. If a DTC sets that forces a switch-over to gasoline operation (for example: DTC P1202), fuel pressure can only be monitored before DTC sets. If vehicle will not idle in CNG mode, note pressures during cranking and go to next step. If vehicle will start and idle, run until operating temperature is reached. Record pressure while engine is idling. Observe and record pressure while performing the following procedures: Apply parking brake. Press and firmly hold brake pedal. Place vehicle in Drive. Depress throttle to 80 percent (power brake) for maximum of 10 seconds. Release throttle and allow engine to idle in neutral for a minimum of 2 minutes for transmission to cool. If recorded pressure values are 4-6 psi (28-41 kPa), go to next step. If recorded pressure values are not 4-6 psi (28-41 kPa), go to step 13.
6. Turn ignition off. Remove LPR secondary test port plug. A small amount of oil may drain from this port. Connect pressure gauge adaptor to secondary test port. Install primary test port plug using teflon sealant, NOT teflon tape. Connect Slack Tube Manometer (J 7333-6) to pressure gauge adaptor. Ensure vent port of manometer is closed until engine is started. Start engine and allow to idle until normal operating temperature is reached. Open vent port on manometer. Record manometer reading at idle. Observe and record manometer reading while performing the following procedures: Apply parking brake. Press and firmly hold brake pedal. Place vehicle in Drive. Depress throttle to 80 percent (power brake) for maximum of 10 seconds. Release throttle and allow engine to idle in neutral for a minimum of 2 minutes for transmission to cool. If recorded manometer values are 4-5 in. H 2 O (5.1-5.7 cm), go to step 19. If recorded manometer values are not 4-5 in. H 2 O (5.1-5.7 cm), go to next step.
7. Check for loose clamps, cracks or deterioration of vapor hoses between LPR and GMS/MCV and between GMS/MCV and Gas Distribution Adaptor (GDA). Check GDA for loose or missing components or physical damage. Check that butterfly valve inside GMS/MCV rotates freely and does not drag when rotated. Repair or replace components as necessary. After repairs, go to step 20. If components are okay, go to step 13.
8. Using scan tool, command LPL on and off. Listen and feel for LPL operation as LPL solenoid is energized and de-energized. If LPL operation is heard or felt when energized, go to next step. If LPL operation is not heard or felt when energized, go to step 15.
9. Using scan tool, command HPL on and off. Listen for HPL operation as HPL solenoid is energized and de-energized. If HPL operation is heard when energized, go to next step. If HPL operation is not heard when energized, go to step 17.
10. Turn ignition off. Remove rubber access plug located on fuel tank cover inside trunk. Verify that manual lock-down Allen screw of HPL is fully seated in a counter-clockwise direction (fully open). If manual lock-down Allen screw is not fully open, open as necessary and go to step 20. If manual lock-down Allen screw is fully open, go to next step.
11. Check fuel line between HPL, HPR and LPR for kinks, bends, damage or obstructions. An obstructed fuel line may be cool or have frost on the surface near obstruction when fuel is flowing through line. Repair or replace as necessary. After repairs, go to step 20. If fuel line is okay, go to next step. NOTE: During next step, rhythmic pressure fluctuations of 10-20 psi are normal. A defective HPR is not indicated unless fluctuations become excessive.
12. Relieve fuel pressure. See FUEL SYSTEM PRESSURE RELEASE under FUEL SYSTEMS in REMOVAL, OVERHAUL & INSTALLATION - CARS article. Replace HPR filter. See HIGH PRESSURE FUEL REGULATOR (2.2L - CAVALIER - CNG) under FUEL SYSTEMS in REMOVAL, OVERHAUL & INSTALLATION - CARS article. Observe pressure while cranking engine. If a DTC sets that forces a switch-over to gasoline operation (for example: DTC P1202), fuel pressure can only be monitored before DTC sets. If vehicle will not idle in CNG mode, note pressures during cranking. If possible, start engine and allow to idle until engine reaches operating temperature. Record pressure at idle. Observe and record pressure while performing the following procedures: Apply parking brake. Press and firmly hold brake pedal. Place vehicle in Drive. Depress throttle to 80 percent (power brake) for maximum of 10 seconds. Release throttle and allow engine to idle in neutral for a minimum of 2 minutes for transmission to cool. If recorded pressure values are 115-220 psi (793-1517 kPa), go to step 17. If recorded pressure values are not 115-220 psi (793-1517 kPa), go to step 14.
13. Replace LPR. See LOW FUEL PRESSURE REGULATOR (2.2L - CAVALIER - CNG) under FUEL SYSTEMS in REMOVAL, OVERHAUL & INSTALLATION - CARS article. After repairs, go to step 20.
14. Replace HPR. See HIGH PRESSURE FUEL REGULATOR (2.2L - CAVALIER - CNG) under FUEL SYSTEMS in REMOVAL, OVERHAUL & INSTALLATION - CARS article. After repairs, go to step 20.
15. Disconnect low pressure lock-off solenoid connector. Connect test light between low pressure lock-off solenoid connector terminals "A" (Purple wire) and "B" (Light Blue wire). Using scan tool, command LPL solenoid on and off. If test light turns on when commanded on, go to next step. If test light does not turn on when commanded on, go to DTC P1215: OUTPUT DRIVER CIRCUIT FAULT (2.2L - CNG) under DIAGNOSTIC TESTS in SELF-DIAGNOSTICS - 2.2L & 2.4L "J" & "N" BODIES - GASOLINE & CNG article.
16. Replace low pressure lock-off solenoid. See LOCK-OFF SOLENOIDS (2.2L - CAVALIER - CNG) under FUEL SYSTEMS in REMOVAL, OVERHAUL & INSTALLATION - CARS article. After repairs, go to step 20.
17. Disconnect high pressure lock-off solenoid connector. Connect test light between high pressure lock-off solenoid connector terminals "A" (White wire) and "B" (Light Green wire). Using scan tool, command HPL solenoid on and off. If test light turns on when commanded on, go to next step. If test light does not turn on when commanded on, go to DTC P1215: OUTPUT DRIVER CIRCUIT FAULT (2.2L - CNG) under DIAGNOSTIC TESTS in SELF-DIAGNOSTICS - 2.2L & 2.4L "J" & "N" BODIES - GASOLINE & CNG article.
18. Replace high pressure lock-off solenoid. See LOCK-OFF SOLENOIDS (2.2L - CAVALIER - CNG) under FUEL SYSTEMS in REMOVAL, OVERHAUL & INSTALLATION - CARS article. After repairs, go to step 20.
19. Observe pressure gauge and turn engine off. If pressure drops to zero within seconds of turning engine off, go to next step. If pressure does not drop to zero within seconds of turning engine off, go to step 16.
20. Relieve fuel pressure. See FUEL SYSTEM PRESSURE RELEASE under FUEL SYSTEMS in REMOVAL, OVERHAUL & INSTALLATION - CARS article. Turn ignition off. Remove all test equipment. Ensure dust caps and plugs are reinstalled. Use teflon sealant on plugs, NOT teflon tape. Start engine and allow to idle. Using Ultrasonic Leak Detector (J 41416), check for leaks between fuel tank and Low Pressure Regulator (LPR). Check for leaks at LPR and between LPR and Gas Distribution Ring (GDR) using SNOOP® or soapy water. Repair any leaks as necessary. Using scan tool, clear any DTCs from AF ECU and PCM. Turn ignition off and wait 30 seconds. Start engine and operate vehicle noting operation of Fuel Indicator Light (FIL) and Malfunction Indicator Light (MIL). Observe vehicle performance and driveability in gasoline and alternate fuel modes. If FIL or MIL do not illuminate and vehicle performs normally, system is okay at this time. If FIL or MIL illuminate or vehicle does not performs normally, go to POWERTRAIN DIAGNOSTIC SYSTEM CHECK (CNG) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 2.2L & 2.4L "J" & "N" BODIES - GASOLINE & CNG article.

Scheme 38

Alternate Fuel Engine Control Unit (AF ECU) and Powertrain Control Module (PCM) are connected by Natural Gas Operation (NGO) enable circuit. For engine to switch-over to CNG operation, PCM must be commanded to disable gasoline fuel injectors, switch to a different ignition spark calibration and disable some PCM DTCs. AF ECU performs switch-over command by grounding NGO enable circuit when CNG operation is desired.

This vehicles primary fuel source is compressed natural gas (CNG). Vehicle will only switch-over to gasoline operation if one of the following conditions is present

1. Fuel Pressure Sensor (FPS) indicates CNG tank is empty.
2. A wide-open Mixture Control Valve (MCV) is detected.
3. System fault is detected by control module (AF ECU or PCM).
4. Manual shut-off valve is closed.
5. Engine crank time exceeds 8 seconds.
6. On every 100th start and also when coolant temperature is less than 10°F (-12°C), vehicle will start and run briefly on gasoline. A switch-over to CNG will occur only during a decel condition.

1. If alternative fuels engine controls diagnostic system check has been performed, go to next step. If alternative fuels engine controls diagnostic system check has not been performed, go to POWERTRAIN DIAGNOSTIC SYSTEM CHECK (CNG) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 2.2L & 2.4L "J" & "N" BODIES - GASOLINE & CNG article. After performing alternative fuels engine controls diagnostic system check, go to next step.
2. Using scan tool, communicate with AF ECU and observe NGO SIGNAL and NGO SIGNAL COMMAND parameters. Start engine while monitoring parameters. If both parameters indicate NATURAL GAS OPERATION is enabled, go to next step. If both parameters do not indicate NATURAL GAS OPERATION is enabled, go to step 5.
3. Monitor Fuel Indicator Light (FIL) located in fuel gauge select switch. If FIL is illuminated, go to MIL ON STEADY (CNG) under SYSTEM TESTS in SELF-DIAGNOSTICS - 2.2L & 2.4L "J" & "N" BODIES - GASOLINE & CNG article. If FIL is not illuminated, go to next step.
4. Fault is not present at this time. If any additional DTCs are set and need to be repaired, go to appropriate diagnostic procedure. See DIAGNOSTIC TROUBLE CODE DEFINITIONS in SELF-DIAGNOSTICS - 2.2L & 2.4L "J" & "N" BODIES - GASOLINE & CNG article. If no additional DTCs are set, go to «DIAGNOSTIC AIDS»(/cadillac/seville/v-1998-2004/remont/testing-diagnostics/#engine-control-system-system-testing-engine-component-tests__diagnostic-aids).
5. Using scan tool, communicate with AF ECU and observe Fuel Pressure Sensor (FPS) parameter. If FPS is more than 1200 psi (8274 kPa), go to next step. If FPS is less than 1200 psi (8274 kPa), go to step 10.
6. Using scan tool, observe NGO SIGNAL parameter and command NGO ENABLE circuit to natural gas operation. If parameter indicates NATURAL GAS OPERATION is enabled, go to next step. If parameter does not indicate NATURAL GAS OPERATION is enabled, go to step 13.
7. Natural gas operation will be disabled if any of the following conditions occur: FPS indicates fuel pressure drops to less than 0.85 volts (350 psi at 70°F or 2412 kPa at 21°C). Natural gas operation will NOT be enabled until fuel pressure sensor indicates fuel pressure is more than 1.50 volts (1000 psi at 70°F or 6890 kPa at 21°C). An AF ECU DTC is set. Not all AF ECU DTCs cause a switch-over to gasoline. A wide-open Mixture Control Valve (MCV) is detected. Check MCV control circuits for proper terminal contact and circuit continuity between MCV and GMS connectors. Engine crank time is more than 8 seconds. The following conditions cause a start-up on gasoline followed by switch-over to natural gas during a vehicle decel condition: An engine coolant temperature of less than 10°F (-12°C) is detected at start-up or every 100th engine start. Test FPS, Engine Coolant Temperature (ECT) sensor and MCV for proper operation. Check FPS accuracy by connecting vehicle to a CNG filling station and verifying tank pressure. Repair as necessary. After repairs, go to step 22. If no problems are found, go to next step. NOTE: A higher secondary voltage is required for CNG. A vehicle that operates normally on gasoline does not indicate a properly operating ignition system. If vehicle starts and stalls, check for malfunctioning Crankshaft Position (CKP) sensor.
8. Check ignition system voltage using ONLY Spark Tester (J 26792). Check CKP sensor for proper parameters using scan tool. Remove spark plugs and check for fouled (wet), cracked, excessively worn, incorrectly gapped, burned electrodes or heavy deposits. Check for damaged spark plug wires. While engine is running, spray plug wires with a fine mist of water and note any crossfire or misfire. Check AF ECU and PCM grounds for proper contact. Repair as necessary. After repairs, go to step 22. If no problems are found, go to next step.
9. Perform fuel system diagnosis. See «FUEL SYSTEM DIAGNOSIS (2.2L - CAVALIER - CNG)»(/cadillac/seville/v-1998-2004/remont/testing-diagnostics/#engine-control-system-system-testing-engine-component-tests). Repair as necessary. After repairs, go to step 22. If fuel system is okay, go to step 21.
10. Start engine and allow to idle. Using scan tool, monitor FPS parameter and command HPL open. If FPS increases to more than 1200 psi (8274 kPa) when HPL is commanded open, go to step 15. If FPS does not increase to more than 1200 psi (8274 kPa) when HPL is commanded open, go to next step. NOTE: Before performing next step, ensure manual lock-down screw of HPL manual shut-off fitting is opened by rotating Allen screw counter-clockwise until fully seated.
11. Verify CNG fuel tank is at full pressure by connecting vehicle to a CNG filling station and filling tank to full capacity. Turn ignition on. Compare dispensing station gauge reading to FPS reading on scan tool. If FPS reading is close to dispensing station gauge reading, go to next step. If FPS reading is not close to dispensing station gauge reading, go to TEST J: FUEL GAUGE INACCURATE/INOPERATIVE (CNG) under SYSTEM TESTS in ANALOG INSTRUMENT PANELS - CAVALIER & SUNFIRE article.
12. While monitoring FPS parameter, start engine and allow to idle. Ensure vehicle is operating on alternate fuel. Monitor FPS reading for a few minutes while engine idles. Review test description. See «DESCRIPTION»(/cadillac/seville/v-1998-2004/remont/testing-diagnostics/#engine-control-system-system-testing-engine-component-tests). If FPS parameter ever drops to less than 1200 psi (8274 kPa), go to step 19. If FPS parameter does not drop to less than 1200 psi (8274 kPa), go to step 22.
13. Observe NGO SIGNAL parameter for PCM. Turn ignition off for 30 seconds. Locate AF ECU and disconnect connectors. AF ECU is located behind left front fascia, below headlight. (Scheme 35) Connect a fused jumper wire between AF ECU Blue connector C001 terminal No. 3 (Pink wire) and ground. (Scheme 39) Turn ignition on. If fused jumper blows, repair short to voltage in Pink wire. If NGO signal indicates natural gas operation is enabled, go to step 16. If NGO signal does not indicate natural gas operation is enabled, go to next step.
14. Check for open in Pink wire between AF ECU and PCM connector C1 terminal No. 71. (Scheme 30) Check for poor connections ate PCM. Check that PCM is calibrated with proper bi-fuel information. Repair circuit connections or program PCM as necessary. After repairs, go to step 22. If no problems are found, go to step 17.
15. Check for fuel system leak or LPL that will not hold pressure when CNG system is closed. Check HPL for proper prime pulse operation. Repair as necessary and go to step 22.
16. Check for poor connections at AF ECU. Repair as necessary. After repairs, go to step 22. If connections are okay, go to step 18.
17. Replace PCM. See POWERTRAIN CONTROL MODULE under COMPUTERIZED ENGINE CONTROLS in REMOVAL, OVERHAUL & INSTALLATION - CARS article. Program (flash) PCM with correct vehicle software and calibration. See POWERTRAIN CONTROL MODULE REPROGRAMMING under PROGRAMMING in SELF-DIAGNOSTICS - 2.2L & 2.4L "J" & "N" BODIES - GASOLINE & CNG article. To perform CKP variation learn procedure, a switch-over to gasoline operation is necessary. Remove CNG fuse (20-amp) located in underhood fuse block to perform switch-over. Perform CKP system variation learn procedure. See CRANKSHAFT POSITION SENSOR SYSTEM VARIATION LEARN PROCEDURE under PROGRAMMING in SELF-DIAGNOSTICS - 2.2L & 2.4L "J" & "N" BODIES - GASOLINE & CNG article. After performing repairs and procedures, go to step 18.
18. Replace AF ECU. See ALTERNATE FUEL ENGINE CONTROL UNIT under COMPUTERIZED ENGINE CONTROLS in REMOVAL, OVERHAUL & INSTALLATION - CARS article. Program (flash) AF ECU with correct vehicle software and calibration. See ALTERNATE FUEL ENGINE CONTROL UNIT under PROGRAMMING in SELF-DIAGNOSTICS - 2.2L & 2.4L "J" & "N" BODIES - GASOLINE & CNG article. After performing repairs and procedures, go to step 18.
19. Locate and disconnect High Pressure Lock-Off (HPL) solenoid connector. (Scheme 35) Connect test light between HPL solenoid connector terminals "A" (White wire) and "B" (Light Green wire). Using scan tool, command HPL solenoid on and off. If test light illuminates when commanded on, go to next step. If test light does not illuminate when commanded on, go to DTC P1215: OUTPUT DRIVER CIRCUIT FAULT (2.2L - CNG) under DIAGNOSTIC TESTS in SELF-DIAGNOSTICS - 2.2L & 2.4L "J" & "N" BODIES - GASOLINE & CNG article.
20. Replace high pressure lock-off solenoid. See LOCK-OFF SOLENOIDS (2.2L - CAVALIER - CNG) under FUEL SYSTEMS in REMOVAL, OVERHAUL & INSTALLATION - CARS article. After repairs, go to step 18.
21. Replace GMS/MCV. See GAS MASS SENSOR/MIXTURE CONTROL VALVE (2.2L - CAVALIER - CNG) under FUEL SYSTEMS in REMOVAL, OVERHAUL & INSTALLATION - CARS article. After repairs, go to next step.
22. Turn ignition off. Remove all test equipment. Reconnect any disconnected components and/or connectors. Using scan tool, clear DTCs from AF ECU and PCM. Turn ignition off for 30 seconds. Start engine and allow to idle. Start engine and operate vehicle noting operation of Fuel Indicator Light (FIL) and Malfunction Indicator Light (MIL). Observe vehicle performance and driveability in gasoline and alternate fuel modes. If FIL or MIL do not illuminate and vehicle performs normally, system is okay at this time. If FIL or MIL illuminate or vehicle does not performs normally, go to POWERTRAIN DIAGNOSTIC SYSTEM CHECK (CNG) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 2.2L & 2.4L "J" & "N" BODIES - GASOLINE & CNG article.

Scheme 39

Diagnostic Aids

Diagnostic information should be utilized only if concern of vehicle operator can be duplicated. An unwanted switch may occur only during specific vehicle operation. Examples of unwanted switch are as follow

1. Vehicle has an intermittently leaking Low Pressure Lock-Off (LPL) solenoid.
2. After turning engine OFF and waiting several minutes, all CNG purges from fuel lines.
3. During next ignition ON key cycle, High Pressure Lock-Off (HPL) solenoid is opened for approximately one second. At the same moment HPL is opened, AF ECU monitors fuel pressure sensor. If LPL is still leaking, CNG pressure cannot build within the system and low fuel pressure is observed by AF ECU. Detecting low fuel pressure in the system, AF ECU performs a switch-over to gasoline.
4. Vehicle may start and run on CNG during any ignition cycle in which LPL does not leak. Customer concern would be an intermittent unwanted switch to gasoline with no DTCs stored and possibly a no-start flooded condition.

If an unwanted switch only occurs during certain driving conditions, perform fuel system diagnosis and verify that fuel pressure can be maintained during all driving conditions. See FUEL SYSTEM DIAGNOSIS .

IDLE CONTROL SYSTEMS

Note. For idle control system testing not listed, perform related DTC testing procedure. See appropriate SELF-DIAGNOSTICS article.

Note. Perform powertrain diagnostic system check prior to testing, and after completing any repairs. See POWERTRAIN DIAGNOSTIC SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article.

1. Perform powertrain diagnostic system check. See appropriate POWERTRAIN DIAGNOSTIC SYSTEM CHECK in SELF-DIAGNOSTICS article.
2. Set parking brake and block drive wheels. Install scan tool. Start engine. Turn all accessories off. Using scan tool RPM control function, slowly increment engine speed to 1800 RPM, then to 600 RPM. Then to 1800 RPM. Exit RPM control function. If engine RPM stabilizes within 60 RPM for automatic transmission and/or within 100 RPM for manual transmission of commanded RPM during test, see «DIAGNOSTIC AIDS»(/cadillac/seville/v-1998-2004/remont/testing-diagnostics/#engine-control-system-system-testing-engine-component-tests) . If engine RPM does not stabilize as specified, go to next step.
3. Turn ignition off. Disconnect IAC valve harness connector. See WIRING DIAGRAMS article. Connect IAC System Motor Analyzer (J 37027-A) to IAC valve. Start engine. Using IAC system motor analyzer, command IAC valve in until about 600 RPM is reached and then command IAC valve out until about 1800 RPM is reached. Return engine RPM to desired idle as indicated on scan tool data list. If engine RPM steadily decreased to about 600 RPM and increased to about 1800 RPM when IAC valve was commanded in and out, go to step 5 . If engine RPM did not decrease and increase as specified, go to next step.
4. If idle RPM is high and can not be controlled by IAC motor driver, go to step 11 . If idle RPM is not high and can be controlled by IAC motor driver, go to step 12 .
5. Using a test light connected to ground, probe one IAC valve circuit at IAC valve harness connector. See WIRING DIAGRAMS article. Start engine. Using IAC system motor analyzer, command low RPM while observing scan tool until IAC counts start to increment, then command high RPM until IAC counts start to increment. Observe test light while incrementing IAC counts. Return engine to idle as indicated on scan tool data list. Repeat procedure for other three IAC valve circuits. If test light remained on (never flashing) while IAC counts where incrementing at any IAC valve circuits during test, go to step 10 . If test light did not remain on while incrementing IAC counts, go to next step.
6. If test light remained off (never flashing) while IAC Counts where incrementing at any IAC valve circuits, go to step 9 . If test light did not remain off, go to next step.
7. Using Connector Test Adaptor Kit (J 35616-A) connect a test light between IAC coil "A" low circuit and IAC coil "A" high circuit at IAC valve harness connector. Using IAC system motor driver, command low RPM while observing scan tool until IAC counts start to increment, then command high RPM until IAC counts start to increment. Observe test light while incrementing IAC counts. Return engine speed to desired idle as indicated on scan tool data list. Repeat procedure on IAC coil "B" low circuit and IAC coil "B" high circuit. If test light stayed illuminated (never flashing) while IAC counts where incrementing, go to next step. If test light did not remained illuminated while IAC counts where incrementing, go to step 16 .
8. Check for poor connection at IAC valve harness connector. Repair as necessary. After repairs, go to step 17 . If IAC valve harness connections are okay, see «DIAGNOSTIC AIDS»(/cadillac/seville/v-1998-2004/remont/testing-diagnostics/#engine-control-system-system-testing-engine-component-tests) .
9. Turn ignition off. Disconnect PCM harness connectors. Check for open or short to ground in IAC valve circuit where test light remained off. Repair as necessary. After repairs, go to step 17 . If circuits are okay, go to step 13 .
10. Turn ignition on. Check for short to voltage on IAC valve circuit where test lamp remained illuminated. Repair as necessary. After repairs, go to step 17 . If circuits are okay, go to step 13
11. Visually and physically inspect for the following: Throttle body damage and tampering. Skewed TP sensor signal. Throttle lever screw tampering (if equipped). Vacuum leaks. Faulty, incorrectly installed PCV valve and hose (if equipped). Throttle shaft binding. Throttle linkage or cruise control linkage binding (if equipped). Remove IAC valve. Inspect for the following: Clogged IAC passage. Excessive deposits on throttle plate. Excessive deposits in throttle bore. Excessive deposits on IAC valve pintle. Repair as necessary. After repairs, go to step 17 . If all listed components are okay, go to step 14 .
12. Visually and physically inspect for the following: Throttle body damage and tampering. Throttle lever screw tampering (if equipped). Restricted air intake system. Excessive deposits on throttle plate. Excessive deposits in throttle bore. Remove IAC valve and inspect for excessive deposits on IAC valve pintle and in IAC valve passage. Repair as necessary. After repairs, go to step 17 . If all listed components are okay, go to step 14 .
13. Check for poor PCM harness connections. Repair as necessary. After repairs, go to step 17 . If PCM connections are okay, go to step 16 .
14. Check for poor IAC valve harness connection. Repair as necessary. After repairs, go to step 17 . If IAC valve harness connection is okay, go to next step.
15. Replace IAC valve. After repairs, go to step 17 .
16. Replace PCM. After repairs, go to next step.
17. Using scan tool, clear any DTCs that may have set. Turn ignition off for 30 seconds. Operate vehicle within conditions to verify repair.

Inspect for the following conditions

1. Skewed high TP sensor.
2. Restricted air intake system.
3. Objects blocking IAC passage or throttle bore.
4. Correct Positive Crankcase Ventilation (PCV) valve, properly installed and proper operation of PCV valve (if equipped).
5. Proper operation and installation of all air intake components.
6. Proper installation and operation of Mass Air Flow (MAF) sensor (if equipped).
7. Tampered with or damaged throttle stop screw.
8. Tampered with or damaged throttle plate, throttle shaft, throttle linkage, or cruise control linkage (if equipped).
9. Excessive deposits in IAC passage or on IAC pintle.
10. Excessive deposits in throttle bore or on throttle plate.
11. Vacuum leaks
12. Excessive engine load caused by faulty transmission, power steering, alternator, etc.
13. High or unstable idle condition caused by a non-IAC system problem that can not be overcome by IAC valve.
14. Low or unstable idle condition caused by a non-IAC system problem that can not be overcome by IAC valve.

IGNITION SYSTEMS

Note. For basic ignition system checks, see appropriate BASIC DIAGNOSTIC PROCEDURES article.

Note. For ignition system testing, perform related DTC testing procedure. See appropriate SELF-DIAGNOSTICS article.

Ignition relay is positive voltage supply source for Gas Mass Sensor/Mixture Control Valve (GMS/MCV) and fuel gauge select switch. Ignition relay coil is energized when ignition switch is turned to Run or Start positions. Ignition relay switch contact is supplied voltage at all times.

1. If alternative fuels engine controls diagnostic system check has been performed, go to next step. If alternative fuels engine controls diagnostic system check has not been performed, go to POWERTRAIN DIAGNOSTIC SYSTEM CHECK (CNG) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 2.2L & 2.4L "J" & "N" BODIES - GASOLINE & CNG article. After performing alternative fuels engine controls diagnostic system check, go to next step.
2. Turn ignition off. Remove and inspect CNG fuse (20-amp) located in underhood fuse block. (Scheme 37) Remove and inspect PCM fuse (10-amp) located in instrument panel fuse block. If either fuse is blown, go to step 13. If both fuses are okay, go to next step.
3. Reinstall CNG and PCM fuses. Turn ignition on. Using a test light connected to ground, probe each terminal of CNG and PCM fuse. If test light illuminates at all terminals, go to step 5. If test light does not illuminate at all terminals, go to next step.
4. Check for poor fuse contact. Check for proper voltage of supply circuit to malfunctioning fuse. See POWER DISTRIBUTION article in WIRING DIAGRAMS. Repair as necessary. After repairs, go to step 22.
5. Turn ignition off. Locate and disconnect Alternate Fuel Engine Control Unit (AF ECU) connectors. AF ECU is located behind left front fascia, below headlight. Turn ignition on. Using a test light connected to ground, probe AF ECU Blue connector C001 terminals No. 13 (Pink wire), No. 15 (Pink wire) and No. 16 (Orange wire). (Scheme 39) If test light illuminates at all terminals, go to next step. If test light does not illuminate at all terminals, go to step 14.
6. Using a test light connected to battery voltage, probe Black wire at AF ECU Clear/White connector C002 terminals No. 21, 22, 23 and 24. (Scheme 39) If test light illuminates at all terminals, go to step 20. If test light does not illuminate at all terminals, go to step 14.
7. Turn ignition off and wait 30 seconds. Monitor Fuel Indicator Light (FIL) located on fuel gauge select switch to left of steering column. Turn ignition on. If FIL illuminates for 2 second bulb check, go to step 9. If FIL does not illuminate for 2 second bulb check, go to next step.
8. Ensure ignition is on. Using test light connected to ground, backprobe ignition relay terminal No. 87 (Red wire). Ignition relay is located below left front headlight. (Scheme 35) If test light illuminates, go to TEST L: FUEL INDICATOR LIGHT INOPERATIVE (CNG) under SYSTEM TESTS in ANALOG INSTRUMENT PANELS - CAVALIER & SUNFIRE article. If test light does not illuminate, go to step 10.
9. Ensure ignition is on. Using test light connected to ground, backprobe ignition relay terminal No. 87 (Red wire). Ignition relay is located below left front headlight. (Scheme 35) Observe test light. Turn ignition off. If test light is illuminated with ignition off, go to step 15. If test light is not illuminated with ignition off, go to POWERTRAIN DIAGNOSTIC SYSTEM CHECK (CNG) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 2.2L & 2.4L "J" & "N" BODIES - GASOLINE & CNG article.
10. Ensure ignition is on. Using test light connected to ground, backprobe ignition relay terminal No. 30 (Orange wire). If test light illuminates, go to next step. If test light does not illuminate, go to step 16.
11. Ensure ignition is on. Using test light connected to ground, backprobe ignition relay terminal No. 85 (Pink wire). If test light illuminates, go to next step. If test light does not illuminate, go to step 17.
12. Disconnect ignition relay. Ignition relay is located below left headlight. (Scheme 35) Ensure ignition is on. Connect test light between ignition relay connector terminals No. 85 (Pink wire) and No. 86 (Black wire). If test light is illuminated, go to step 19. If test light is not illuminated, go to step 18.
13. Check for cause of blown fuse. For blown CNG fuse, check for the following conditions: Shorted GMS/MCV circuit. Shorted fuel gauge select switch circuit. Shorted lock-off solenoid or circuit. Shorted AF ECU or AF ECU battery voltage supply circuit. For blown PCM fuse, check for the following conditions: Shorted ignition relay coil or circuit. Shorted AF ECU or AF ECU ignition voltage supply circuit. Shorted base vehicle circuit. See POWER DISTRIBUTION article in WRING DIAGRAMS. Repair as necessary. After repairs, go to step 22.
14. Repair open in AF ECU circuit that did not illuminate test light. After repairs, go to step 22.
15. Replace stuck ignition relay or repair short to battery voltage in Pink wire between CLS/PCM fuse (10-amp) located in instrument panel fuse block and ignition relay connector terminal No. 85. After repairs, go to step 22.
16. Repair open in Orange wire between ignition relay connector terminal No. 30 and splice S001 located approximately 1.5" (3.5 cm) from the 4 relay break outs, towards AF ECU connector break outs. After repairs, go to step 22.
17. Repair open in Pink wire between ignition relay connector terminal No. 85 and splice S028 located approximately 6" (14 cm) from ignition relay connector. After repairs, go to step 22.
18. Repair open in Black wire between ignition relay connector terminal No. 86 and ground connection located on left side of engine/transmission. After repairs, go to step 22.
19. Replace ignition relay. After repairs, go to step 22.
20. Check for poor connections at AF ECU connectors. Repair as necessary. After repairs, go to step 22. If connections are okay, go to next step.
21. Replace AF ECU. See ALTERNATE FUEL ENGINE CONTROL UNIT under COMPUTERIZED ENGINE CONTROLS in REMOVAL, OVERHAUL & INSTALLATION - CARS article. Program (flash) AF ECU with correct vehicle software and calibration. See ALTERNATE FUEL ENGINE CONTROL UNIT under PROGRAMMING in SELF-DIAGNOSTICS - 2.2L & 2.4L "J" & "N" BODIES - GASOLINE & CNG article. After performing repairs and procedures, go to next step.
22. Turn ignition off. Remove all test equipment. Reconnect any disconnected components and/or connectors. Using scan tool, clear DTCs from AF ECU and PCM. Turn ignition off for 30 seconds. Start engine and allow to idle. Start engine and operate vehicle noting operation of Fuel Indicator Light (FIL) and Malfunction Indicator Light (MIL). Observe vehicle performance and driveability in gasoline and alternate fuel modes. If FIL or MIL do not illuminate and vehicle performs normally, system is okay at this time. If FIL or MIL illuminate or vehicle does not performs normally, go to POWERTRAIN DIAGNOSTIC SYSTEM CHECK (CNG) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 2.2L & 2.4L "J" & "N" BODIES - GASOLINE & CNG article.

EMISSION SYSTEMS & SUBSYSTEMS

Note. For emission and subsystem testing not listed, perform related DTC testing procedure. See appropriate SELF-DIAGNOSTICS article.

Electric AIR Pump

Note. For electric AIR pump testing, perform related DTC testing procedure. See appropriate SELF-DIAGNOSTICS article.

EXHAUST GAS RECIRCULATION

Note. Manufacturer does not provide testing procedures for many individual systems and components. For EGR system testing not listed, perform related DTC testing procedure. See appropriate SELF-DIAGNOSTICS article.

Note. For EGR system diagnosis, see appropriate INSPECTION/MAINTENANCE PROCEDURES in appropriate SELF-DIAGNOSTICS article.

Exhaust System Check

1. Remove heated oxygen sensor. Install exhaust backpressure tester in place of oxygen sensor. Start engine and let idle. If pressure reading is not 1.25 psi or greater, go to next step. If pressure reading is 1.25 psi or greater, go to step 3 .
2. Increase engine speed to 2000 RPM. If pressure reading is greater than 3 psi, go to next step. If pressure reading is not greater than 3 psi, go to step 5 .
3. Check exhaust system for crushed pipe, internal muffler damage or heat distress. If problem does not exist, go to next step. If problem exists, repair as necessary and go to step 5 .
4. Replace catalytic converter. After repairs, go to next step.
5. Operate vehicle within conditions under which original symptom was noted. If system operate properly, system is okay. If system does not operate properly, go to step 1 .

FUEL EVAPORATION

Note. Ensure all vacuum line and EVAP system components are not damaged or missing before proceeding with this test.

EVAP Control System Diagnosis (3.1L Lumina)

1. Perform powertrain diagnostic system check. See appropriate POWERTRAIN DIAGNOSTIC SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article.
2. If any DTC is set, perform appropriate DTC test in appropriate SELF-DIAGNOSTICS article. If DTC is not set, go to next step.
3. Check EVAP system for the following conditions: Loose, incorrect, defective or missing fuel fill cap. Improperly routed, kinked or damaged EVAP system purge or vapor pipes. Pinched off or damaged fresh air vent hose. Damaged EVAP system components. Loose, missing or damaged service port dust cap and/or Schrader valve. Repair as necessary. After repairs, go to step 9 . If above system checks are okay, go to next step.
4. Disconnect EVAP vapor pipe from fuel tank or EVAP canister. Turn ignition on, engine off. Using scan tool, observe fuel tank pressure parameter. If fuel tank pressure is about zero, go to next step. If fuel tank pressure is not about zero, see DTC P0453 in appropriate SELF-DIAGNOSTICS article.
5. Reconnect all EVAP hardware. Install Fuel Tank Cap Adapter (J 41415-40) to fuel fill neck and fuel fill cap. Connect EVAP Pressure/Purge Diagnostic Station (J 41413) to fuel tank cap adaptor. Using scan tool, select SEAL option to seal EVAP system. Using EVAP station, pressurize system to 5 in. H2O (1.25 kPa) by slowly turning rotary switch to PRESSURE position. DO NOT exceed 5 in. H2O (1.25 kPa) pressure. If 5 in. H2O (1.25 kPa) is achieved, go to next step. If 5 in. H2O (1.25 kPa) is not achieved, see DTC P0440 in appropriate SELF-DIAGNOSTICS article.
6. Using EVAP diagnostic station, maintain fuel tank pressure at 5 in. H2O (1.25 kPa). If scan tool indicates fuel tank pressure of 5 in. H2O (1.25 kPa), go to next step. If fuel tank pressure is not 5 in. H2O (1.25 kPa), see DTC P0452 in appropriate SELF-DIAGNOSTICS article.
7. Using scan tool, command vent valve off. If pressure decrease is about 0 in. H2O (0 kPa) within 2 minutes with rotary switch in OFF/HOLD position, go to next step. If pressure decrease is not as specified, see DTC P0446 in appropriate SELF-DIAGNOSTICS article.
8. Using EVAP station, increase fuel tank pressure to 5 in. H2O (1.25 kPa). Using scan tool, observe fuel tank pressure. If scan tool indicates fuel tank pressure decrease to 0 in. H2O (0 kPa) within 15 seconds, see DTC P1441 in appropriate SELF-DIAGNOSTICS article. If fuel tank pressure is not as specified, go to next step.
9. Reconnect all EVAP hardware. Turn ignition on, engine off. Using scan tool, select SEAL option to seal EVAP system. Do not exceed 15 in H2O pressure. Using EVAP station, pressurize system to 15 in. H2O by slowly turning rotary switch to PRESSURE position. Monitor pressure with gauge on cart with rotary switch in OFF/HOLD position. If EVAP pressure decrease is less than 10 in. H2O within 2 minutes, see DTC P0442 in appropriate SELF-DIAGNOSTICS article. If pressure is as specified, system is okay.

EVAP Control System Diagnosis (Except 3.1L Lumina)

Note. The following procedure does not apply to 2.2L Saturn.

For EVAP control system diagnosis, see appropriate INSPECTION/MAINTENANCE PROCEDURES in appropriate SELF-DIAGNOSTICS article.

Required Service

The PCV system may require service for obstructions if any of the following conditions exist

1. Rough idle.
2. Stalling or slow idle speed.
3. Oil leaks.
4. Oil in air cleaner.
5. Sludge in engine.

A leaking PCV valve or hose could cause

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

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

Checking PCV Valve Function

1. Disconnect PCV valve vacuum hose from cylinder head cover. Run engine at idle. Place thumb over open end of PCV valve vacuum hose to check for vacuum. If vacuum does not exist, check for obstruction in source vacuum supply. If source vacuum supply is okay, replace PCV valve.
2. Turn ignition off. Remove PCV valve. Shake valve and listen for rattle of check valve inside PCV valve. If a clear rattle is not heard, replace PCV valve.
3. Visually inspect valve for varnish or deposits which may make PCV valve operation sticky or restricted, or cause incomplete seating of valve. Replace as necessary.
4. Engine must be sealed for PCV system to function as designed. If leakage, sludging or dilution of oil is noted and PCV system is functioning properly, check engine for cause and repair as required to ensure PCV system will continue to function properly.
5. An engine operating without any crankcase ventilation can be damaged, so it is important to replace PCV valve and air cleaner breather (if equipped) at regular intervals (at least every 30,000 miles). Check all hoses and clamps for failure or deterioration.

MISCELLANEOUS CONTROLS

Note. Although some of the controlled devices listed here are not technically engine performance components, they can affect driveability if they malfunction.

Note. Manufacturer does not provide testing procedures for many individual systems and components. For system and component testing not listed, perform related DTC testing procedure. See appropriate SELF-DIAGNOSTICS article.

A/C COMPRESSOR CLUTCH CONTROLS

Note. For A/C compressor clutch circuit testing, see appropriate MANUAL A/C-HEATER SYSTEMS article in AIR CONDITIONING & HEATING.

ELECTRIC COOLING FAN

Note. For electric cooling fan circuit testing, see appropriate ELECTRIC COOLING FANS article in ENGINE COOLING.

TRANSMISSION

Note. For transmission electronic controls testing, see appropriate ELECTRONIC CONTROLS article in AUTOMATIC TRANSMISSIONS. For component circuit identification, see WIRING DIAGRAMS article.

COMPONENT LOCATIONS

Note. Component location tables for Saturn vehicles are not available. Refer to appropriate illustrations. (Scheme 40)- (Scheme 46).

COMPONENT LOCATIONS (2.2L VIN 4 & 2.4L VIN T - CAVALIER & SUNFIRE - GASOLINE)

COMPONENT LOCATIONS (2.2L VIN 4 & 2.4L VIN T - CAVALIER & SUNFIRE - GASOLINE)

COMPONENT LOCATIONS (2.2L VIN 4 & 2.4L VIN T - CAVALIER & SUNFIRE - CNG)

Note. Component locations for 2.2L VIN 4 & 2.4L VIN T - CAVALIER & SUNFIRE - CNG vehicles apply to CNG components only. For gasoline components, see COMPONENT LOCATIONS (2.2L VIN 4 & 2.4L VIN T - CAVALIER & SUNFIRE - GASOLINE) .

COMPONENT LOCATIONS (2.2L VIN 4 & 2.4L VIN T - CAVALIER & SUNFIRE - CNG)

COMPONENT LOCATIONS (2.4L VIN T - ALERO & GRAND AM)

COMPONENT LOCATIONS (2.4L VIN T - ALERO & GRAND AM)

COMPONENT LOCATIONS (3.0L VIN R - CATERA)

COMPONENT LOCATIONS (3.0L VIN R - CATERA)

COMPONENT LOCATIONS (3.1L VIN J - CENTURY)

COMPONENT LOCATIONS (3.1L VIN J - CENTURY)

COMPONENT LOCATIONS (3.1L VIN J - MALIBU)

COMPONENT LOCATIONS (3.1L VIN J - MALIBU)

COMPONENT LOCATIONS (3.1L VIN J - LUMINA)

COMPONENT LOCATIONS (3.1L VIN J - LUMINA)

COMPONENT LOCATIONS (3.1L VIN J - GRAND PRIX)

COMPONENT LOCATIONS (3.1L VIN J - GRAND PRIX)

COMPONENT LOCATIONS (3.4L VIN E - ALERO & GRAND AM)

COMPONENT LOCATIONS (3.4L VIN E - ALERO & GRAND AM)

COMPONENT LOCATIONS (3.4L VIN E - IMPALA & MONTE CARLO)

COMPONENT LOCATIONS (3.4L VIN E - IMPALA & MONTE CARLO)

COMPONENT LOCATIONS (3.5L VIN H - AURORA)

COMPONENT LOCATIONS (3.5L VIN H - AURORA)

COMPONENT LOCATIONS (3.5L VIN H - INTRIGUE)

COMPONENT LOCATIONS (3.5L VIN H - INTRIGUE)

COMPONENT LOCATIONS (3.8L VIN K & 1 - BONNEVILLE, LESABRE & PARK AVENUE)

COMPONENT LOCATIONS (3.8L VIN K & 1 - BONNEVILLE, LESABRE & PARK AVENUE)

COMPONENT LOCATIONS (3.8L VIN K - CAMARO & FIREBIRD)

COMPONENT LOCATIONS (3.8L VIN K - CAMARO & FIREBIRD)

COMPONENT LOCATIONS (3.8L VIN K & 1 - GRAND PRIX)

COMPONENT LOCATIONS (3.8L VIN K & 1 - GRAND PRIX)

COMPONENT LOCATIONS (3.8L VIN K - IMPALA & MONTE CARLO)

COMPONENT LOCATIONS (3.8L VIN K - IMPALA & MONTE CARLO)

COMPONENT LOCATIONS (3.8L VIN K & 1 - REGAL)

COMPONENT LOCATIONS (3.8L VIN K & 1 - REGAL)

COMPONENT LOCATIONS (4.0L VIN C - AURORA)

COMPONENT LOCATIONS (4.0L VIN C - AURORA)

COMPONENT LOCATIONS (4.6L VIN Y & 9 - DEVILLE, ELDORADO & SEVILLE)

COMPONENT LOCATIONS (4.6L VIN Y & 9 - DEVILLE, ELDORADO & SEVILLE)

COMPONENT LOCATIONS (5.7L VIN G - CAMARO & FIREBIRD)

COMPONENT LOCATIONS (5.7L VIN G - CAMARO & FIREBIRD)

COMPONENT LOCATIONS (5.7L VIN G - CORVETTE)

COMPONENT LOCATIONS (5.7L VIN G - CORVETTE)

Scheme 40

Scheme 41

Scheme 42

Scheme 43

Scheme 44

Scheme 45

Scheme 46

See also:
• MODEL IDENTIFICATION
• COMPONENT LOCATIONS
• IDLE CONTROL SYSTEM
• FUEL INJECTOR COIL TEST
• INJECTOR COIL TEST DIAGNOSTIC AIDS
• FUEL INJECTOR BALANCE TEST
• DIAGNOSTIC AIDS