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Engine Control System - System Testing & Engine Component Tests: Diagnosis Oldsmobile Alero I

Testing & Diagnostics 5 illustrations ~9695 words

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 .

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»(ref-128919-S26268796292001110600000) .
  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.
Application(1) psi (kg/cm 2 )
2.2L & 2.4L53-59 (3.8-4.2)
3.0L40-46 (2.8-3.2)
3.1L & 3.4L52-59 (3.7-4.2)
3.5L, 4.0L & 4.6L41-47 (2.9-3.3)
3.8L
Camaro & Firebird48-54 (3.4-3.8)
Bonneville, Grand Prix, Park Avenue & Regal48-55 (3.4-3.9)
All Others52-59 (3.7-4.2)
5.7L55-62 (3.9-4.4)
(1) Specification listed is with ignition on and engine off.
(1)Specification listed is with ignition on and engine off.

FUEL PRESSURE SPECIFICATIONS (EXCEPT SATURN)

Application(1) psi (kg/cm 2 )
1.9L40-55 (2.8-3.9)
2.2L50-59 (3.5-4.2)
3.0L65 (4.6)
(1) Specification listed is with ignition on and engine off.
(1)Specification listed is with ignition on and engine off.

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»(ref-128919-S24247316652001111400000) .
  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»(ref-128919-S24247316652001111400000) . 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.

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 43) 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 43) 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 43) 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. see scheme 1and (Scheme 44). 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 43

Scheme 43
Scheme 43

Scheme 44

Scheme 44
Scheme 44
  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 45) 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 43) 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 43) 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 43) 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 47) 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 47) 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 45

Scheme 45
Scheme 45

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 46) 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 46) 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 46

Scheme 46
Scheme 46
  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»(ref-128919-S04063784992002010400000).
  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)»(ref-128919-S01365648772001121000000). 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»(ref-128919-S18211714422002010400000). 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 43) Connect a fused jumper wire between AF ECU Blue connector C001 terminal No. 3 (Pink wire) and ground. (Scheme 47) 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. see scheme 1 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 43) 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 47

Scheme 47
Scheme 47

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 .

  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»(ref-128919-S04787606292001111400000) . 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»(ref-128919-S04787606292001111400000) .
  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.
  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 45) 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 47) 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 47) 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 43) 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 43) 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 43) 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.

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.

More articles — Engine Control System - System Testing & Engine Component Tests