Engine Control System Testing & Engine Component Testing Chevrolet Impala VIII

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 .

Description

The boost control solenoid is a normally open valve. Under most conditions, the Powertrain Control Module (PCM) commands the boost control solenoid to operate at 100 percent duty cycle, which closes the solenoid valve to allow the system to boost. This is achieved by allowing manifold vacuum to reach the top port of the bypass valve actuator through the inlet vacuum signal hose. With the boost control solenoid closed, vacuum from the boost source hose can not reach the lower port of the bypass valve actuator to disable boost. However, if reverse gear is selected, the PCM detects deceleration, engine temperature is extremely high, or drive train abuse is detected, then reduced boost pressure is desired. Under these conditions the PCM commands the boost control solenoid to operate at 0 percent duty cycle, which opens the solenoid valve and allows vacuum to pass from the boost source hose, through the boost control solenoid and boost signal hose, to the bypass valve actuator lower port. This disables boost by opening the bypass valve. With the bypass valve open, boost pressure is reduced by recirculating intake air back through the supercharger inlet.

Diagnostic Procedures

1. Perform Diagnostic System Check - Engine Controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in appropriate SELF-DIAGNOSTICS article. After performing Diagnostic System Check - Engine Controls, go to next step.
2. Inspect the following items and repair any condition as necessary: Vacuum lines for cracking, restrictions, and loose fit. The bypass valve actuator for sticking, binding, or damage. The bypass valve for sticking, binding, or damage. The bypass valve linkage for binding or damage. The boost control solenoid for damage. Did you find and correct the condition? If yes, go to step 16 . If no, go to next step.
3. Disconnect the boost signal hose from the bypass valve actuator. Connect a vacuum gauge to the boost signal hose. Start and idle the engine in park. Does the vacuum gauge read near 0 in. Hg? If yes, go to next step. If no, go to step 10 .
4. Connect a scan tool and command the boost control solenoid to 0 percent duty cycle. Observe the vacuum gauge. Does the vacuum gauge read more than 15 in. Hg? If yes, go to next step. If no, go to step 8 .
5. Turn OFF the ignition. Reconnect the boost signal hose to the bypass valve actuator. Disconnect the inlet vacuum signal hose from the bypass valve actuator. Connect a vacuum gauge to the inlet vacuum signal hose. Start and idle the engine in park. Does the vacuum gauge read more than 15 in. Hg? If yes, go to next step. If no, go to step 13 .
6. Turn OFF the ignition. Connect a vacuum pump to the inlet vacuum signal port on the bypass valve actuator. Slowly apply vacuum to 15 in. Hg. Does the bypass valve actuator retract? If yes, go to next step. If no, go to step 11 .
7. Reconnect the inlet vacuum signal hose to the bypass valve actuator. Disconnect the boost signal hose from the bypass valve actuator. Connect a vacuum pump to the boost signal port on the bypass valve actuator. Start and idle the engine in park. Slowly apply vacuum to 20 in. Hg. Does the bypass valve actuator extend? If yes, system is okay. If no, go to step 11 .
8. Turn OFF the ignition. Reconnect the boost signal hose to the bypass valve actuator. Disconnect the boost signal hose from the boost control solenoid. Connect a vacuum gauge to the boost signal port on the boost control solenoid. Start and idle the engine in park. Command the boost control solenoid to 0 percent duty cycle. Does the vacuum gauge read more than 15 in. Hg? If yes, go to step 15 . If no, go to next step.
9. Turn OFF the ignition. Disconnect the boost source hose from the boost control solenoid. Connect a vacuum gauge to the boost source hose. Start and idle the engine in park. Does the vacuum gauge read more than 15 in. Hg? If yes, go to next step. If no, go to step 14 .
10. Replace the boost control solenoid. After repairs, go to step 16 .
11. Inspect the bypass valve and bypass valve actuator linkage for binding, sticking or damage. Repair any condition as necessary. Did you find and correct a condition? If yes, go to step 16 . If no, go to next step.
12. Replace the bypass valve actuator. After repairs, go to step 16 .
13. Repair the inlet vacuum signal hose for a restriction or blockage. After repairs, go to step 16 .
14. Repair the boost source hose for a restriction or blockage. After repairs, go to step 16 .
15. Repair the boost signal hose for a restriction or blockage. After repairs, go to next step.
16. Reconnect any disconnected components. Use the scan tool in order to clear any DTCs that may have set. Turn OFF the ignition for 30 seconds. Operate the vehicle within conditions to verify the repair. Did you verify the repair? If yes, go to next step. If no, go to step 2 .
17. With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS in appropriate SELF-DIAGNOSTICS article. If no, system is okay.

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. For connector terminal identification, see appropriate SELF-DIAGNOSTICS article. See WIRING DIAGRAMS article. Resistance should be less than 5 ohms. If resistance is not less than 5 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. For connector terminal identification, see appropriate SELF-DIAGNOSTICS article. 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. For connector terminal identification, see appropriate SELF-DIAGNOSTICS article. See WIRING DIAGRAMS article. If harness is open or shorted, repair as necessary.

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 .

The Manifold Absolute Pressure (MAP) sensor responds to pressure changes in the intake manifold which gives an indication of the engine load. The MAP sensor has the following circuits

1. A 5-volt reference circuit.
2. A low reference circuit.
3. A signal circuit.

The Powertrain Control Module (PCM) supplies 5 volts to the MAP sensor on the 5-volt reference circuit and provides a ground on the low reference circuit. The MAP sensor provides a signal to the PCM on the signal circuit which is relative to the pressure changes in the manifold. With low MAP such as during idle or deceleration, the PCM should detect a low signal voltage. With high MAP such as ignition ON, with the engine OFF or Wide Open Throttle (WOT), the PCM should detect a high signal voltage. Certain vehicle models will also use the MAP sensor in order to calculate the Barometric (BARO) pressure when the ignition switch is turned ON, with the engine OFF. The BARO reading may also be updated whenever the engine is operated at WOT. The PCM monitors the MAP sensor signal for voltage outside of the normal range. If the PCM detects a MAP sensor signal voltage that is excessively high, DTC P0108 will set. If the PCM detects a MAP sensor signal voltage that is excessively low, DTC P0107 will set.

Test Description

The number below refers to the step number in the diagnostic procedures.

1. 2 This step tests the MAP sensor's ability to correctly indicate BARO. The BARO varies with altitude and atmospheric conditions. 103 kPa is the approximate BARO displayed by the MAP sensor at or near sea level.

1. Perform Diagnostic System Check - Engine Controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in appropriate SELF-DIAGNOSTICS article. After performing Diagnostic System Check - Engine Controls, go to next step.
2. Install a scan tool. Turn ON the ignition, with the engine OFF. With the scan tool observe the MAP sensor pressure. Compare this value to a value observed in a known-good vehicle. Is the difference between the two vehicles less than 3 kPa? If yes, go to next step. If no, go to step 7 .
3. Observe the MAP sensor pressure on the scan tool. Start the engine. Does the MAP sensor value change? If yes, go to next step. If no, go to step 7 .
4. Turn OFF the ignition. Remove the MAP sensor from the engine vacuum source. Leave the MAP sensor connected to the engine harness. Connect a Vacuum Pump (J 23738-A) to the MAP sensor. Turn ON the ignition, with the engine OFF. Observe the MAP sensor pressure as you SLOWLY apply vacuum 1 in. Hg at a time. Each one inch of vacuum should result in a 3 to 4 kPa drop in the MAP sensor pressure. Does the scan tool indicate that the MAP sensor is operating normally? If yes, go to next step. If no, go to step 15 .
5. Observe the MAP sensor pressure on the scan tool with 20 inches Hg of vacuum applied to the sensor. Is the pressure less than 34 kPa? If yes, go to next step. If no, go to step 7 .
6. Disconnect the MAP sensor from the J 23738-A. The MAP sensor pressure should return to the value observed in step 2 . Does the MAP sensor pressure return to the value observed earlier? If yes, system is okay. If no, go to step 15 .
7. Turn OFF the ignition. Disconnect the MAP sensor from the engine harness. Turn ON the ignition, with the engine OFF. Observe the MAP sensor VOLTAGE display on the scan tool. Is the voltage more than 0.1 V? If yes, go to step 11 . If no, go to next step.
8. Connect a test lamp to a good ground. Probe the 5-volt reference circuit of the MAP sensor with the test lamp. Perform a voltage drop test across the test lamp with a DMM. Does the voltage measure more than 4.4 V? If yes, go to next step. If no, go to step 12 .
9. Jumper the MAP sensor 5-volt reference circuit to the MAP sensor signal circuit using a fused jumper wire. Does the scan tool indicate that the MAP sensor voltage is near 5 V? If yes, go to next step. If no, go to step 13 .
10. Remove the jumper. Disconnect the electrical connector of the Engine Coolant Temperature (ECT) sensor. Probe the MAP sensor low reference circuit with a test lamp connected to battery positive voltage. Does the test lamp illuminate? If yes, go to step 15 . If no, go to step 14 .
11. Test the signal circuit for a short to voltage. Did you find and correct the condition? If yes, go to step 19 . If no, go to step 17 .
12. Test the 5-volt reference circuit of the MAP sensor for high resistance or an open. Did you find and correct the condition? If yes, go to step 19 . If no, go to step 17 .
13. Test the signal circuit for the following conditions: High resistance. An open. A short to ground. Did you find and correct the condition? If yes, go to step 19 . If no, go to step 17 .
14. Test the MAP sensor low reference circuit for high resistance or an open. Did you find and correct the condition? If yes, go to step 19 . If no, go to step 17 .
15. Inspect the MAP sensor connector for poor connection or terminal contact. Did you find and correct the condition? If yes, go to step 19 . If no, go to next step.
16. Replace the MAP sensor. After repairs, go to step 19 .
17. Inspect the PCM for poor connection or terminal contact. Did you find and correct the condition? If yes, go to step 19 . If no, go to next step.
18. Replace PCM. Program replacement PCM. See POWERTRAIN CONTROL MODULE under PROGRAMMING in appropriate SELF-DIAGNOSTICS article. After repairs, go to next step.
19. Use the scan tool in order to clear the DTCs that may have set. Turn OFF the ignition for 30 seconds. Start the engine. Did you correct the condition? If yes, system is okay. If no, go to step 2 .

Diagnostic Aids

Inspect for the following conditions

1. Restrictions in the MAP sensor vacuum source.
2. MAP sensor seal missing or damaged.
3. Vacuum hoses disconnected, damaged, or incorrectly routed.
4. Intake manifold vacuum leaks.
5. Vacuum leaks at the throttle body.
6. Vacuum leaks at the Exhaust Gas Recirculation (EGR) valve flange and pipes.

The Manifold Absolute Pressure (MAP) sensor responds to pressure changes in the intake manifold which gives an indication of the engine load. The MAP sensor has the following circuits

1. A 5-volt reference circuit.
2. A low reference circuit.
3. A signal circuit.

The Powertrain Control Module (PCM) supplies 5 volts to the MAP sensor on the 5-volt reference circuit and provides a ground on the low reference circuit. The MAP sensor provides a signal to the PCM on the signal circuit which is relative to the pressure changes in the manifold. With low MAP such as during idle or deceleration, the PCM should detect a low signal voltage. With high MAP such as ignition ON, with the engine OFF or Wide Open Throttle (WOT), the PCM should detect a high signal voltage. Certain vehicle models will also use the MAP sensor in order to calculate the Barometric (BARO) pressure when the ignition switch is turned ON, with the engine OFF. The BARO reading may also be updated whenever the engine is operated at WOT. The PCM monitors the MAP sensor signal for voltage outside of the normal range. If the PCM detects a MAP sensor signal voltage that is excessively high, DTC P0108 will set. If the PCM detects a MAP sensor signal voltage that is excessively low, DTC P0107 will set.

The number below refers to the step number in the diagnostic procedures.

1. 2 This step tests the MAP sensor's ability to correctly indicate BARO. The BARO varies with altitude and atmospheric conditions. 103 kPa is the approximate BARO displayed by the MAP sensor at or near sea level.

1. Perform Diagnostic System Check - Engine Controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in appropriate SELF-DIAGNOSTICS article. After performing Diagnostic System Check - Engine Controls, go to next step.
2. Install a scan tool. Turn ON the ignition, with the engine OFF. With the scan tool, observe the MAP sensor pressure. Compare this value to a value observed in a known-good vehicle. Is the difference between the vehicles less than 3 kPa? If yes, go to next step. If no, go to step 7 .
3. Observe the MAP sensor pressure on the scan tool. Start the engine. Does the MAP sensor value change? If yes, go to next step. If no, go to step 7 .
4. Turn OFF the ignition. Remove the MAP sensor from the engine vacuum source. Leave the MAP sensor connected to the engine harness. Connect a Hand Vacuum Pump (J 23738-A) to the MAP sensor port. Turn ON the ignition, with the engine OFF. Observe the MAP sensor pressure as you slowly apply vacuum 1 in. Hg at a time. Each one inch of vacuum should result in a 3 to 4 kPa drop in the MAP sensor pressure. Does the scan tool indicate that the MAP sensor is operating normally? If yes, go to next step. If no, go to step 13 .
5. Observe the MAP sensor pressure on the scan tool with 20 in. Hg of vacuum applied to the sensor. Is the MAP sensor pressure less than 34 kPa? If yes, go to next step. If no, go to step 7 .
6. Disconnect the MAP sensor from the hand held vacuum pump. Does the MAP sensor pressure return to the value observed in step 2 ? If yes, system is okay. If no, go to step 13 .
7. Turn OFF the ignition. Disconnect the MAP sensor from the engine harness. Turn ON the ignition, with the engine OFF. Observe the MAP sensor voltage display on the scan tool. Is the voltage more than 0 V? If yes, go to step 10 . If no, go to next step.
8. Jumper the MAP sensor 5-volt reference circuit to the MAP sensor signal circuit using a fused jumper wire. Observe the MAP sensor voltage display on the scan tool. Is the voltage near 5 V? If yes, go to next step. If no, go to step 11 .
9. Remove the jumper. Probe the MAP sensor low reference circuit with a test lamp connected to battery positive voltage. Does the test lamp illuminate? If yes, go to step 13 . If no, go to step 12 .
10. Test the signal circuit for a short to voltage. This short will have resistance as a complete short would have set a DTC. Did you find and correct the condition? If yes, go to step 17 . If no, go to step 15 .
11. Test the 5-volt reference and the signal circuit for high resistance or an open. Did you find and correct the condition? If yes, go to step 17 . If no, go to step 15 .
12. Test the MAP sensor low reference circuit for high resistance or an open. Did you find and correct the condition? If yes, go to step 17 . If no, go to step 15 .
13. Inspect the MAP sensor connector for poor connection or terminal contact. Did you find and correct the condition? If yes, go to step 17 . If no, go to next step.
14. Replace the MAP sensor. After repairs, go to step 17 .
15. Inspect the PCM for poor connection or terminal contact. Did you find and correct the condition? If yes, go to step 17 . If no, go to next step.
16. Replace PCM. Program replacement PCM. See POWERTRAIN CONTROL MODULE under PROGRAMMING in appropriate SELF-DIAGNOSTICS article. After repairs, go to next step.
17. Use the scan tool in order to clear the DTCs that may have set. Turn OFF the ignition for 30 seconds. Start the engine. Did you correct the condition? If yes, system is okay. If no, go to step 2 .

Inspect for the following conditions

1. Restrictions in the MAP sensor vacuum source.
2. MAP sensor seal missing or damaged.
3. Vacuum hoses disconnected, damaged, or incorrectly routed.
4. Intake manifold vacuum leaks.
5. Vacuum leaks at the throttle body.
6. Vacuum leaks at the Exhaust Gas Recirculation (EGR) valve flange and pipes.

PARK NEUTRAL POSITION SWITCH

See appropriate DIAGNOSIS 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 MOTOR

See IDLE CONTROL SYSTEM .

A/C COMPRESSOR CLUTCH RELAY

See appropriate MANUAL 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.

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 DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in appropriate SELF-DIAGNOSTICS article.

Note. For location of components, see COMPONENT LOCATIONS .

FUEL DELIVERY

Note. See appropriate FUEL SYSTEM PRESSURE TEST article under BASIC FUEL SYSTEM CHECKS in BASIC DIAGNOSTIC PROCEDURES - CARS - EXCEPT PRIZM article.

Fuel Pump Circuit

See FUEL PUMP ELECTRICAL CIRCUIT DIAGNOSIS under appropriate NO-START - ENGINE CRANKS OKAY article under NO-START DIAGNOSIS in BASIC DIAGNOSTIC PROCEDURES - CARS - EXCEPT PRIZM article.

Fuel Pressure Regulator

See appropriate FUEL SYSTEM PRESSURE TEST article under BASIC FUEL SYSTEM CHECKS in BASIC DIAGNOSTIC PROCEDURES - CARS - EXCEPT PRIZM article.

The scan tool first energizes the fuel pump and then the injectors for a precise amount of time allowing a measured amount of fuel into the manifold. This causes a drop in system fuel pressure that can be recorded and used to compare each injector.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 3 The Engine Coolant Temperature (ECT) must be below the operating temperature in order to avoid irregular fuel pressure readings due to hot soak fuel boiling.
2. 4 The fuel pressure should be within the specified range. See «FUEL PRESSURE SPECIFICATIONS (EXCEPT SATURN)»(/chevrolet/impala/viii-1999-2006/remont/testing-diagnostics/#engine-control-system-testing-engine-component-testing) table or «FUEL PRESSURE SPECIFICATIONS (SATURN)»(/chevrolet/impala/viii-1999-2006/remont/testing-diagnostics/#engine-control-system-testing-engine-component-testing) table. If the fuel pressure is not within the specified range, see appropriate FUEL SYSTEM PRESSURE TEST article under BASIC FUEL SYSTEM CHECKS in BASIC DIAGNOSTIC PROCEDURES - CARS - EXCEPT PRIZM article.
3. 5 The fuel pressure should reach a steady value. See appropriate FUEL SYSTEM PRESSURE TEST article under BASIC FUEL SYSTEM CHECKS in BASIC DIAGNOSTIC PROCEDURES - CARS - EXCEPT PRIZM article.
4. 6 If the pressure drop value for each fuel injector is within 1.5 psi of the average pressure drop value, the fuel injectors are flowing properly. Calculate the pressure drop value for each fuel injector by subtracting the second pressure reading from the first pressure reading.

1. Perform Diagnostic System Check - Engine Controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in appropriate SELF-DIAGNOSTICS article. After performing Diagnostic System Check - Engine Controls, go to next step.
2. 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»(/chevrolet/impala/viii-1999-2006/remont/testing-diagnostics/#engine-control-system-testing-engine-component-testing) .
3. Observe the ECT parameter on the scan tool. Does the scan tool indicate that the ECT parameter is less than 201°F (94°C)? If yes, go to next step. If no, allow engine to cool below 201°F (94°C), then go to next step.
4. Turn OFF the ignition. Turn OFF all accessories. Install the fuel pressure gauge. Turn ON the ignition, with the engine OFF. Command the fuel pump ON with a scan tool. The fuel pump may need to be commanded ON a few times in order to obtain the highest possible fuel pressure. DO NOT start the engine. Observe the fuel pressure gauge, with the fuel pump commanded ON. Is the fuel pressure within the specified value? See «FUEL PRESSURE SPECIFICATIONS (EXCEPT SATURN)»(/chevrolet/impala/viii-1999-2006/remont/testing-diagnostics/#engine-control-system-testing-engine-component-testing) table or «FUEL PRESSURE SPECIFICATIONS (SATURN)»(/chevrolet/impala/viii-1999-2006/remont/testing-diagnostics/#engine-control-system-testing-engine-component-testing) table. If yes, go to next step. If no, see appropriate FUEL SYSTEM PRESSURE TEST article under BASIC FUEL SYSTEM CHECKS in BASIC DIAGNOSTIC PROCEDURES - CARS - EXCEPT PRIZM article.
5. Monitor the fuel pressure gauge for 1 minute. Does the fuel pressure decrease by more than 5 psi? If yes, see appropriate FUEL SYSTEM PRESSURE TEST article under BASIC FUEL SYSTEM CHECKS in BASIC DIAGNOSTIC PROCEDURES - CARS - EXCEPT PRIZM article. If no, go to next step.
6. With a scan tool, select the Fuel Injector Balance Test function, within the Special Functions menu. Select an injector to be tested. Press Enter. This will prime the fuel system. Record the fuel pressure indicated by the fuel pressure gauge after the fuel pressure stabilizes. This is the 1st pressure reading. Record the fuel pressure value immediately after the fuel injector stops pulsing. The fuel pressure may rise after the fuel injector stops pulsing. DO NOT record the higher fuel pressure value. Energize the fuel injector by depressing the Pulse Injector button on the scan tool. This will energize the injector and decrease the fuel pressure. Record the fuel pressure indicated by the fuel pressure gauge after the fuel injector has stopped pulsing. This is the 2nd pressure reading. Press Enter again to bring you back to the Select Injector screen. Repeat for each fuel injector. Subtract the 2nd pressure reading from the 1st pressure reading for one fuel injector. The result is the pressure drop value. Obtain a pressure drop value for each fuel injector. Add all of the individual pressure drop values. This is the total pressure drop. Divide the total pressure drop by the number of fuel injectors. This is the average pressure drop. Does any fuel injector have a pressure drop value that is either higher than the average pressure drop or lower than the average pressure drop by 1.5 psi? If yes, go to next step. If no, see appropriate TROUBLE SHOOTING - NO CODES article.
7. Replace the affected fuel injectors. After repairs, go to next step.
8. Operate the system in order to verify the repair. Did you correct the condition? If yes, system is okay. If no, see appropriate TROUBLE SHOOTING - NO CODES article.

FUEL PRESSURE SPECIFICATIONS (EXCEPT SATURN)

FUEL INJECTOR BALANCE TEST (SATURN)

Note. If engine is at operating temperature, allow a 10 minute cool down period.

1. On the SOHC engine, remove air intake tube.
2. Before the Fuel Injector Balance Test is started, the electrical connector should be tested using a Noid Light (J34730). Disconnect electrical connectors at fuel injectors. Connect a noid light to the female connector. Crank the engine. If the noid light does not blink, the electrical problem must be corrected before continuing.
3. Connect Gauge Bar Set (SA9127E) to fuel test port.
4. Connect the Electronic Fuel Injection Tester (SA9182E). Connect the plug to a fuel injector. Connect the red clip to the positive battery post. Connect the black clip to a clean ground. Check the power light. If it is not on, check the battery connection again.
5. Set the switch on the fuel injector tester to the 50 Pulse-10 MS setting.
6. Cycle the ignition key On/Off several times (do not start engine) and bleed off all air in the system using the pressure gauge shut-off valve.
7. Turn the ignition to the Off position for ten seconds. After ten seconds, turn ignition key to the On position (do not start engine) and record gauge pressure (1st reading).
8. Using the injector tester, pulse injector No. 1.
9. Record pressure at the instant the gauge needle stops moving (2nd reading).
10. Repeat steps 6 through 9 for the remaining injectors.
11. Add all the 2nd Readings together and divide by 4 (this is the 2nd reading Average).
12. Subtract Average of 2nd Readings from each 2nd Reading to obtain the Difference.
13. An injector is faulty if the Difference is greater than plus or minus 1.5 psi.
14. Check that all fuel injector connectors are connected. Pull back to ensure a positive engagement.
15. Remove fuel gauge bar adapter from fuel pressure test port and recap it.
16. Install air intake tube.
17. Start engine and check for leaks.

FUEL PRESSURE SPECIFICATIONS (SATURN)

The Powertrain Control Module (PCM) enables the appropriate fuel injector on the intake stroke for each cylinder. A voltage is supplied directly to the fuel injectors. The PCM controls each fuel injector by grounding the control circuit via a solid state device called a driver. A fuel injector coil winding resistance that is too high, or low, will affect engine driveability. A fuel injector control circuit DTC may not set, but a misfire may be apparent. The fuel injector coil windings are affected by temperature. The resistance of the fuel injector coil windings will increase as the temperature of the fuel injector increases.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 3 This step tests each fuel injector resistance within a specific temperature range. If any of the fuel injectors display a resistance outside of the specified value, replace the fuel injector.
2. 4 This step determines if all of the fuel injectors are within 3 ohms of each other. If the highest resistance value is within 3 ohms of the lowest resistance value, then all of the fuel injector coil windings are okay.
3. 5 This step determines which fuel injector is faulty. After subtracting the highest and lowest resistance values from the average value, replace the fuel injector that has the greatest resistance difference from the average.

1. Perform Diagnostic System Check - Engine Controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in appropriate SELF-DIAGNOSTICS article. After performing Diagnostic System Check - Engine Controls, go to next step.
2. Using scan tool, check Engine Coolant Temperature (ECT). Is the ECT value within 50-90°F (10-32°C)? If yes, go to next step. If no, go to step 4 .
3. Disconnect fuel injector connector. Using DVOM, measure resistance of each fuel injector. Do any of the fuel injectors display a resistance outside 11-14 ohms? If yes, go to step 6 . If no, see «DIAGNOSTIC AIDS»(/chevrolet/impala/viii-1999-2006/remont/testing-diagnostics/#engine-control-system-testing-engine-component-testing) .
4. Disconnect fuel injector connector. Using DVOM, measure resistance of each fuel injector. Record each fuel injector value. Subtract lowest resistance value from highest resistance value. Is the difference equal to, or less than, 3 ohms? If yes, see «DIAGNOSTIC AIDS»(/chevrolet/impala/viii-1999-2006/remont/testing-diagnostics/#engine-control-system-testing-engine-component-testing) . If no, 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. Did you correct the condition? If yes, system is okay. If no, go to step 2 .

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. Remove air induction tube and resonator.
2. Relieve fuel system pressure. See «FUEL SYSTEM PRESSURE RELIEF (SATURN)»(/chevrolet/impala/viii-1999-2006/remont/testing-diagnostics/#engine-control-system-basic-diagnostic-procedures__fuel-system-pressure-relief-saturn) under BASIC FUEL SYSTEM CHECKS in BASIC DIAGNOSTIC PROCEDURES - CARS - EXCEPT PRIZM.
3. Remove throttle cable from throttle cable support bracket.
4. Remove upper power steering support brace.
5. Connect Gauge Bar Set (SA9127E) to fuel pressure port.
6. Remove fuel feed line clip attachment nut.
7. Remove fuel rail assembly attachment bolts and pull fuel rail back far enough so that the nozzles of the fuel injectors are visible but still in ports. Attach the fuel rail to the intake manifold with safety wire.
8. Connect fuel pressure gauge bar to pressure adapter.
9. Wipe the tips of the fuel injectors free of any fuel or debris and place a clean White towel directly under fuel injectors. The clean White towel must lightly contact each fuel injector tip. This will serve as an indicator of leaky fuel injectors by showing spots where fuel has leaked as well as block the injector ports from any debris that might enter.
10. Connect scan tool and turn ignition On.
11. Energize fuel pump using scan tool and observe the fuel injector tips for leakage of fuel. If one or more of the White towels becomes wet with fuel after five minutes, replace the faulty fuel injector. It is very difficult to measure drops of fuel from a injector. Pressure gauge reading should be approximately 40-55 psi (276-379 kPa).
12. Test assembly a minimum of two times.
13. Install bleed hose from Pressure Test Adapter (309725) into an approved container and open valve to bleed system pressure. Once pressure is bled, remove fuel gauge adapter from the fuel pressure test port and recap it.
14. Lubricate injector "O" rings with clean engine oil and install fuel rail assembly.
15. Start engine and check for leaks.

INJECTOR LEAK TEST (2.2L SATURN)

1. Remove air cleaner inlet tube.
2. Relieve fuel system pressure. See «FUEL SYSTEM PRESSURE RELIEF (SATURN)»(/chevrolet/impala/viii-1999-2006/remont/testing-diagnostics/#engine-control-system-basic-diagnostic-procedures__fuel-system-pressure-relief-saturn) under BASIC FUEL SYSTEM CHECKS in BASIC DIAGNOSTIC PROCEDURES - CARS - EXCEPT PRIZM.
3. Connect Pressure Gauge Adapter (309725) to fuel pressure test port.
4. Remove fuel line attachment screw and fuel lines from clamp.
5. Remove fuel rail assembly. Pull fuel rail back far enough so that nozzles of injectors are visible but still in ports. Attach fuel rail to intake manifold with wire.
6. Connect fuel pressure gauge bar to pressure adapter.
7. Wipe tips of fuel injectors free of any fuel or debris. Place a clean White towel directly under fuel injectors. Ensure towel lightly contacts each fuel injector tip.
8. Connect scan tool and turn ignition On. Battery must be at a minimum of 12 volts when performing any fuel system test. Charge battery before proceeding if below 12 volts.
9. Using the scan tool, energize fuel pump.
10. Observe fuel injector tips for leakage of fuel. If one or more of White towels becomes wet with fuel after five minutes, replace faulty fuel injector. Pressure gauge reading should be approximately 50-60 psi (345-414 kPa).
11. Test assembly a minimum of two times.
12. Install bleed hose from Pressure Test Adapter (309725) into an approved container.
13. Open valve to bleed system pressure.
14. Remove fuel pressure adapter from fuel pressure test port.
15. Install fuel pressure test port cap.
16. Lubricate injector "O" rings with clean engine oil and install fuel rail assembly.
17. Start engine and check for leaks.

INJECTOR LEAK TEST (3.0L)

1. Relieve fuel system pressure. See «FUEL SYSTEM PRESSURE RELIEF (SATURN)»(/chevrolet/impala/viii-1999-2006/remont/testing-diagnostics/#engine-control-system-basic-diagnostic-procedures__fuel-system-pressure-relief-saturn) under BASIC FUEL SYSTEM CHECKS in BASIC DIAGNOSTIC PROCEDURES - CARS - EXCEPT PRIZM.
2. Connect Fuel Flow/Pressure Adapter (SA9127E-7) to fuel pressure test port.
3. Remove fuel rail assembly. Pull fuel rail back far enough so that nozzles of injectors are visible but still in ports. Attach fuel rail to intake manifold with wire.
4. Connect Gauge Bar Set (SA9127E) to pressure adapter.
5. Wipe tips of fuel injectors free of any fuel or debris. Place a clean White towel directly under fuel injectors. Ensure towel lightly contacts each fuel injector tip.
6. Connect scan tool and turn ignition On. Battery must be at a minimum of 12 volts when performing any fuel system test. Charge battery before proceeding if below 12 volts.
7. Using scan tool, energize fuel pump.
8. Observe fuel injector tips for leakage of fuel. If one or more of the White towels becomes wet with fuel after five minutes, replace faulty fuel injector. Pressure gauge reading should be approximately 40-50 psi (276-345 kPa).
9. Test assembly a minimum of two times.
10. Install bleed hose from fuel flow/pressure adapter into an approved container.
11. Open valve to bleed system pressure.
12. Remove fuel pressure adapter from fuel pressure test port.
13. Install fuel pressure test port cap. Replace plastic fuel line retainers whenever fuel supply lines are disconnected at fuel filter and fuel rail. Install new retainer into female portion of connection. Care must be taken to assure that locking tab is centered in window of female connection. Firmly press male and female portions together until a "click" is heard, then pull firmly back to confirm engagement.
14. Lubricate injector "O" rings with clean engine oil and install fuel rail assembly.
15. Start engine and check for leaks.

See FUEL PUMP RELAY under MOTORS, RELAYS & SOLENOIDS.

FUEL SYSTEMS (2.2L - CAVALIER CNG)

Note. For location of components, see COMPONENT LOCATIONS .

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 Module (AF ECM) when vehicle is operating in CNG mode. At initial ignition on request, AF ECM 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 ECM closes driver and supplies ground path. When engine is cranking or running, AF ECM closes BOTH lock-off solenoid control circuit drivers, allowing engine to operate on CNG.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 1 The System Check must be performed before proceeding with this diagnostic test. Failure to perform the System Check will result in misdiagnosis.
2. 2 This step checks the battery voltage supply from the lock-off relay to the LPL. The lock-off relay is energized regardless of which fuel system is operating the vehicle.
3. 3 This step checks the AF ECM and the Low Pressure Lock-Off Solenoid Control circuit for proper operation. The test lamp should illuminate for a few seconds then turn OFF as the engine cannot start on CNG with the LPL disconnected.
4. 4 This step checks the battery voltage supply from the lock-off relay to the HPL. The lock-off relay is energized regardless of which fuel system is operating the vehicle.
5. 5 This step check the AF ECM and the High Pressure Lock-Off Solenoid Control circuit for proper operation. The test lamp should illuminate for a few seconds then turn OFF as the AF ECM opens the HPL for system priming prior to cranking the engine.
6. 6 This step checks for proper battery voltage output from the lock-off relay.
7. 7 This step checks for proper relay coil positive voltage and ground supply.
8. 8 This step checks for proper battery voltage supply from the CNG fuse (20-amp) circuit to the lock-off relay. If the test lamp fails to illuminate the failure can only exist between the relay and the circuit splice. For example: a blown fuse would cause a lack of power to the AF ECM causing no scan tool communication in which the OBD System Check would have directed you to a different diagnostic procedure.
9. 9 This step checks for proper positive voltage supply from the gasoline fuel pump circuit to the lock-off relay.

1. If powertrain diagnostic system check has been performed, go to next step. If powertrain diagnostic system check has not been performed, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-140667-S19215153262002052400000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 2.2L CAVALIER - CNG article. After performing powertrain diagnostic system check, go to next step.
2. Turn ignition off. Locate and disconnect Low Pressure Lock-Off (LPL) solenoid connector. (Scheme 41) 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 ECM. 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 High Pressure Lock-Off (HPL) solenoid connector. (Scheme 41) 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 41) 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 ECM. 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 ECM 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. For connector terminal identification, see «CONNECTOR IDENTIFICATION»(ref-140667-S31111358522002052400000) in SELF-DIAGNOSTICS - 2.2L CAVALIER - CNG article. (Scheme 42) Check for poor connections at PCM and ICM connectors. Repair as necessary. After repairs, go to step 20. If circuit and connections are okay, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-140667-S19215153262002052400000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 2.2L CAVALIER - 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 ECM. See «ALTERNATE FUEL ENGINE CONTROL MODULE»(ref-150258-S32258339112002110700000) under COMPUTERIZED ENGINE CONTROLS in REMOVAL, OVERHAUL & INSTALLATION - CAVALIER & SUNFIRE article. Program (flash) AF ECM with correct vehicle software and calibration. See «ALTERNATE FUEL ENGINE CONTROL MODULE»(ref-140667-S13949165432002052400000) under PROGRAMMING in SELF-DIAGNOSTICS - 2.2L CAVALIER - 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 ECM 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, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-140667-S19215153262002052400000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 2.2L CAVALIER - CNG article.

Scheme 41

Scheme 42

Alternate Fuel Engine Control Module (AF ECM) supplies power to AF fuel pump relay coil when engine starts and runs on CNG. AF fuel pump relay allows AF ECM 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 ECM. 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 ECM energizes AF fuel pump relay, turning off the gasoline fuel pump. Lock-off relay continues to be energized by gasoline fuel pump relay.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 1 The Diagnostic System Check - Engine Controls must be performed before proceeding with this diagnostic test. Failure to perform the OBD System Check will result in misdiagnosis.
2. 2 This step tests if the engine will start and run. A failure that causes the engine to not start on either fuel can be isolated to the CNG harness or a base vehicle problem such as a malfunctioning gasoline fuel pump relay.
3. 3 This step tests the gasoline control modules ability to supply power to the gasoline fuel pump circuit.
4. 5 This step tests for voltage through the AF fuel pump relay. With the ignition ON and the engine OFF the AF ECM does not energize the AF fuel pump relay allowing voltage to flow through the relay and energize the gasoline fuel pump.
5. 6 This step tests the AF ECMs ability to energize the AF fuel pump relay and disable the gasoline fuel pump during CNG operation.
6. 7 This step tests for stuck AF fuel pump relay contacts or a shorted AF Fuel Pump Relay control circuit.
7. 10 If the engine did not operate on gasoline during the Diagnostic System Check - Engine Controls but now operates on gasoline inspect for intermittent terminal contact or a AF fuel pump relay with sticking contacts that may have been disturbed during testing.
8. 11 This step tests if the CNG harness is the cause of the no-start on gasoline.
9. 15 If the Fuel Pump Power circuit tests okay there is a base vehicle problem that is causing the no-start 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, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-140667-S19215153262002052400000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 2.2L CAVALIER - 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 43) 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 41) 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 vehicle does not operate on CNG or gasoline, or only operates on gasoline, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-140667-S19215153262002052400000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 2.2L CAVALIER - CNG article.
5. Turn ignition off and wait 30 seconds. Locate AF fuel pump relay. (Scheme 41) 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 ECM. 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 41) 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, the 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 & 2.4L - ALERO, CAVALIER, GRAND AM & SUNFIRE)»(/chevrolet/impala/viii-1999-2006/remont/testing-diagnostics/#engine-control-system-basic-diagnostic-procedures__no-start-engine-cranks-okay) under NO-START DIAGNOSIS in BASIC DIAGNOSTIC PROCEDURES - CARS - EXCEPT 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, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-140667-S19215153262002052400000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 2.2L CAVALIER - 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 ECM Blue connector C001 terminal No. 30. (Scheme 45) 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 ECM Blue connector C001 terminal No. 30. (Scheme 45) 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 ECM. See «ALTERNATE FUEL ENGINE CONTROL MODULE»(ref-150258-S32258339112002110700000) under COMPUTERIZED ENGINE CONTROLS in REMOVAL, OVERHAUL & INSTALLATION - CAVALIER & SUNFIRE article. Program (flash) AF ECM with correct vehicle software and calibration. See «ALTERNATE FUEL ENGINE CONTROL MODULE»(ref-140667-S13949165432002052400000) under PROGRAMMING in SELF-DIAGNOSTICS - 2.2L CAVALIER - 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 ECM 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, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-140667-S19215153262002052400000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 2.2L CAVALIER - CNG article.

Scheme 43

Alternative Fuel Engine Control Module (AF ECM) controls fuel system while vehicle is operating on alternative fuel. AF ECM 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 ECM 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 ECM 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 ECM 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 ECM. 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).

The numbers below refer to the step numbers in the diagnostic procedures.

1. 3 This step tests the fuel pressure output of the High Pressure Regulator (HPR).
2. 5 This step tests the fuel pressure output of the Primary Stage of the Low Pressure Regulator (LPR).
3. 6 CNG fuel may contain small amounts of fill station compressor oil. As the CNG fuel pressure drops in the LPR secondary chamber this oil separates from the CNG fuel and collects in the secondary chamber. Allow the oil to drain as this condition is normal and no repair is required. This step tests the fuel pressure output of the Secondary Stage of the Low Pressure Regulator (LPR).
4. 8 This step tests for the sound of a functioning LPL. A circuit failure to solenoid should set a DTC.
5. 9 This step tests for the sound of a functioning HPL. A circuit failure to solenoid should set a DTC.
6. 10 This step tests for a restricted High Pressure Regulator (HPR) filter. If a restricted HPR filter is found also inspect the fill valve filter for contamination, damage or restriction.
7. 11 This step inspects for a closed manual lock-down screw.
8. 12 This step inspects for damage to the fuel line between the HPL and the LPR.
9. 19 This step tests for a leaking LPL. A leaking LPL would allow CNG fuel to enter the engine after the ignition has been turned OFF. The leaking LPL could cause a hard or no-start condition during the next ignition cycle. A leaking LPL would cause the gauge to indicate fuel pressure for up to several minutes after the ignition has been turned OFF.
10. 20 This step tests for proper operation of the system after repairs are complete.

Diagnostic Procedure

1. Perform Diagnostic System Check - Engine Controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-140667-S19215153262002052400000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 2.2L CAVALIER - CNG article. If any DTCs other than P1202 are set, diagnose those DTCs first. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-140667-S18589168882002052400000) in SELF-DIAGNOSTICS - 2.2L CAVALIER - 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 1/3 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 44) Using parts included in CNG Electronic Pressure Gauge Set (J 39970), install Fuel Test Port Adapter (J 39970-100) onto fuel pressure test port. Connect Electronic Fuel Pressure Gauge (J 39970) to adapter. 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 44) Connect pressure gauge adapter to LPR primary test port. Connect 0-15 PSI Pressure Gauge (J 28552) to adapter. 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 2-64 psi, go to next step. If recorded pressure values are not 2-64 psi, 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 adapter 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 adapter. 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 2-5 in. H 2 O (5.1-12.7 cm), go to step 19. If recorded manometer values are not 2-5 in. H 2 O (5.1-12.7 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 Adapter (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 (CNG)»(ref-150258-S41180194732002110700000) under FUEL SYSTEMS (CNG ENGINE) in REMOVAL, OVERHAUL & INSTALLATION - CAVALIER & SUNFIRE article. Replace HPR filter. See «HIGH PRESSURE FUEL REGULATOR»(ref-150258-S33518118192002110700000) under FUEL SYSTEMS (CNG ENGINE) in REMOVAL, OVERHAUL & INSTALLATION - CAVALIER & SUNFIRE 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 PRESSURE REGULATOR»(ref-150258-S28245829532002110700000) under FUEL SYSTEMS (CNG ENGINE) in REMOVAL, OVERHAUL & INSTALLATION - CAVALIER & SUNFIRE article. After repairs, go to step 20.
14. Replace HPR. See «HIGH PRESSURE FUEL REGULATOR»(ref-150258-S33518118192002110700000) under FUEL SYSTEMS (CNG ENGINE) in REMOVAL, OVERHAUL & INSTALLATION - CAVALIER & SUNFIRE 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: GROUND FAULT DETECTION INDICATED»(ref-140667-S09177120322002052400000) under DIAGNOSTIC TESTS in SELF-DIAGNOSTICS - 2.2L CAVALIER - CNG article.
16. Replace low pressure lock-off solenoid. See «LOW PRESSURE LOCK-OFF SOLENOID»(ref-150258-S26568693392002110700000) under FUEL SYSTEMS (CNG ENGINE) in REMOVAL, OVERHAUL & INSTALLATION - CAVALIER & SUNFIRE 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: GROUND FAULT DETECTION INDICATED»(ref-140667-S09177120322002052400000) under DIAGNOSTIC TESTS in SELF-DIAGNOSTICS - 2.2L CAVALIER - CNG article.
18. Replace high pressure lock-off solenoid. See «HIGH PRESSURE LOCK-OFF»(ref-150258-S06620230142002111200000) under FUEL SYSTEMS (CNG ENGINE) in REMOVAL, OVERHAUL & INSTALLATION - CAVALIER & SUNFIRE 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 (CNG)»(ref-150258-S41180194732002110700000) under FUEL SYSTEMS (CNG ENGINE) in REMOVAL, OVERHAUL & INSTALLATION - CAVALIER & SUNFIRE 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 ECM 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 perform normally, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-140667-S19215153262002052400000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 2.2L CAVALIER - CNG article.

Scheme 44

Alternate Fuel Engine Control Module (AF ECM) and Powertrain Control Module (PCM) are connected by the Alternative Fuels Operation (AFO) 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 ECM performs switch-over command by grounding AFO 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 Tank Pressure (FTP) sensor indicates CNG tank is empty.
2. A wide-open Mixture Control Valve (MCV) is detected.
3. System fault is detected by control module (AF ECM 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.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 1 The System Check must be performed before proceeding with this diagnostic procedure. Failure to perform the System Check will result in misdiagnosis.
2. 2 This step inspects if the AF ECM has commanded the gasoline control module, using the AFO Enable circuit, to start on CNG. The AFO Signal Command parameter is the commanded state of the AFO Enable circuit from the AF ECM. The AFO Signal parameter is the monitored state of the AFO Enable circuit from the GASOLINE control module (PCM).
3. 3 This step inspects if the FIL is illuminated during CNG operation. The FIL should illuminate only during gasoline operation.
4. 5 This step inspects if the FTP sensor is monitoring adequate fuel tank pressure for the vehicle to start on CNG.
5. 6 This step tests the ability of the AF ECM to command Alternative Fuels Operation (AFO) and the gasoline control modules ability to monitor the command.
6. 7 This step indicates all the possibilities that cause a switch-over to gasoline operation.
7. 8 This step inspects the ignition system of the vehicle for proper operation. A vehicle that operates correctly on gasoline but not on CNG may have a faulty ignition system.
8. 9 Performing the Fuel System Diagnosis checks the basic AF fuel system for proper pressures and lock-off solenoid operation.
9. 10 A fuel system that is unable to retain fuel pressure after the ignition is turned OFF may cause an Unwanted Switch to Gasoline. The AF ECM commands the HPL open for about 1 second every time the ignition is turned ON. If the fuel line system leaks during ignition OFF the next ignition ON prime pulse will usually recharge the fuel lines and the FTP sensor. A sluggish HPL may not open enough during the 1 second prime pulse but will open when commanded with the scan tool.
10. 11 This step tests for proper fuel tank pressure sensor operation.
11. 12 This step tests for an inoperative HPL. After connecting to a CNG dispensing station the CNG fuel lines, the FTP sensor and the fuel tank will be charged by the station. The CNG fuel pressure in the lines and the FTP sensor will quickly drop if the engine is operating on CNG but the HPL fails to open.
12. 13 This step tests for proper operation of the AFO Enable circuit and the gasoline control module.
13. 15 This step tests for a leaking fuel system with a sluggish HPL.

1. If alternative fuels Diagnostic System Check - Engine Controls has been performed, go to next step. If alternative fuels Diagnostic System Check - Engine Controls has not been performed, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-140667-S19215153262002052400000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 2.2L CAVALIER - CNG article. After performing alternative fuels engine controls diagnostic system check, go to next step.
2. Using scan tool, communicate with AF ECM and observe AFO SIGNAL and AFO 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»(ref-140667-S01707024172002052400000) under SYSTEM TESTS in SELF-DIAGNOSTICS - 2.2L CAVALIER - 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»(ref-140667-S18589168882002052400000) in SELF-DIAGNOSTICS - 2.2L CAVALIER - CNG article. If no additional DTCs are set, go to «DIAGNOSTIC AIDS»(/chevrolet/impala/viii-1999-2006/remont/testing-diagnostics/#engine-control-system-testing-engine-component-testing).
5. Using scan tool, communicate with AF ECM and observe fuel pressure sensor parameter. If fuel pressure sensor is more than 1200 psi (8274 kPa), go to next step. If fuel pressure sensor is less than 1200 psi (8274 kPa), go to step 10.
6. Using scan tool, observe AFO SIGNAL parameter and command AFO 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: Fuel pressure sensor indicates fuel pressure drops to less than 0.85 volt (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 ECM DTC is set. Not all AF ECM 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 FTP sensor, 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 ECM 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»(/chevrolet/impala/viii-1999-2006/remont/testing-diagnostics/#engine-control-system-testing-engine-component-testing). 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 fuel pressure parameter and command HPL open. If fuel pressure increases to more than 1200 psi (8274 kPa) when HPL is commanded open, go to step 15. If fuel pressure 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 FTP sensor reading is close to dispensing station gauge reading, go to next step. If FTP sensor reading is not close to dispensing station gauge reading, go to FUEL GAUGE INACCURATE/INOPERATIVE (CNG) under SYSTEM TESTS in appropriate ANALOG INSTRUMENT PANELS article.
12. While monitoring fuel pressure parameter, start engine and allow to idle. Ensure vehicle is operating on alternate fuel. Monitor fuel pressure reading for a few minutes while engine idles. Review test description. See «DESCRIPTION»(/chevrolet/impala/viii-1999-2006/remont/testing-diagnostics/#engine-control-system-testing-engine-component-testing). If fuel pressure parameter ever drops to less than 1200 psi (8274 kPa), go to step 19. If fuel pressure parameter does not drop to less than 1200 psi (8274 kPa), go to step 22.
13. Observe AFO SIGNAL parameter for PCM. Turn ignition off for 30 seconds. Locate AF ECM and disconnect connectors. AF ECM is located behind left front fascia, below headlight. (Scheme 41) Connect a fused jumper wire between AF ECM Blue connector C001 terminal No. 3 (Pink wire) and ground. (Scheme 45) Turn ignition on. If fused jumper blows, repair short to voltage in Pink wire. If AFO signal indicates natural gas operation is enabled, go to step 16. If AFO signal does not indicate natural gas operation is enabled, go to next step.
14. Check for open in Pink wire between AF ECM and PCM connector C1 terminal No. 71. For connector terminal identification, see «CONNECTOR IDENTIFICATION»(ref-140667-S31111358522002052400000) in SELF-DIAGNOSTICS - 2.2L CAVALIER - CNG article. 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 ECM. Repair as necessary. After repairs, go to step 22. If connections are okay, go to step 18.
17. Replace PCM. See «POWERTRAIN CONTROL MODULE»(ref-150258-S17158143372002110700000) under COMPUTERIZED ENGINE CONTROLS in REMOVAL, OVERHAUL & INSTALLATION - CAVALIER & SUNFIRE article. Program (flash) PCM with correct vehicle software and calibration. See «POWERTRAIN CONTROL MODULE REPROGRAMMING»(ref-140667-S34504727982002052400000) under PROGRAMMING in SELF-DIAGNOSTICS - 2.2L CAVALIER 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»(ref-140667-S39992957302002052400000) under PROGRAMMING in SELF-DIAGNOSTICS - 2.2L CAVALIER - CNG article. After performing repairs and procedures, go to step 18.
18. Replace AF ECM. See «ALTERNATE FUEL ENGINE CONTROL MODULE»(ref-150258-S32258339112002110700000) under COMPUTERIZED ENGINE CONTROLS in REMOVAL, OVERHAUL & INSTALLATION - CAVALIER & SUNFIRE article. Program (flash) AF ECM with correct vehicle software and calibration. See «ALTERNATE FUEL ENGINE CONTROL MODULE»(ref-140667-S13949165432002052400000) under PROGRAMMING in SELF-DIAGNOSTICS - 2.2L CAVALIER - CNG article. After performing repairs and procedures, go to step 18.
19. Locate and disconnect High Pressure Lock-Off (HPL) solenoid connector. (Scheme 41) 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: GROUND FAULT DETECTION INDICATED»(ref-140667-S09177120322002052400000) under DIAGNOSTIC TESTS in SELF-DIAGNOSTICS - 2.2L CAVALIER - CNG article.
20. Replace high pressure lock-off solenoid. See «HIGH PRESSURE LOCK-OFF»(ref-150258-S06620230142002111200000) under FUEL SYSTEMS (CNG ENGINE) in REMOVAL, OVERHAUL & INSTALLATION - CAVALIER & SUNFIRE article. After repairs, go to step 18.
21. Replace GMS/MCV. See «GAS MASS SENSOR/MIXTURE CONTROL VALVE»(ref-150258-S12929915382002110700000) under FUEL SYSTEMS (CNG ENGINES) in REMOVAL, OVERHAUL & INSTALLATION - CAVALIER & SUNFIRE 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 ECM 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, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-140667-S19215153262002052400000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 2.2L CAVALIER - CNG article.

Scheme 45

Scheme 46

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 ECM monitors fuel pressure sensor. If LPL is still leaking, CNG pressure cannot build within the system and low fuel pressure is observed by AF ECM. Detecting low fuel pressure in the system, AF ECM 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 DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in appropriate SELF-DIAGNOSTICS article.

The engine idle speed is controlled by the Idle Air Control (IAC) valve. The IAC valve is on the throttle body. The IAC valve pintle moves in and out of an idle air passage bore to control air flow around the throttle plate. The valve consists of a movable pintle, driven by a gear attached to a two phase bi-polar permanent magnet electric motor called a stepper motor. The stepper motor is capable of highly accurate rotation, or of movement, called steps. The stepper motor has two separate windings that are called coils. Each coil is fed by two circuits from the Powertrain Control Module (PCM). When the PCM changes polarity of a coil, the stepper motor moves one step. The PCM uses a predetermined number of counts to determine the IAC pintle position. Observe IAC counts with a scan tool. The IAC counts will increment up or down as the PCM attempts to change the IAC valve pintle position. An IAC Reset will occur when the ignition key is turned OFF. First, the PCM will seat the IAC pintle in the idle air passage bore. Second, the PCM will retract the pintle a predetermined number of counts to allow for efficient engine start-up. If the engine idle speed is out of range for a calibrated period of time, an idle speed Diagnostic Trouble Code (DTC) may set.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 5 This test determines the ability of the PCM and IAC valve circuits to control the IAC valve.
2. 7 This test determines the ability of the PCM to provide the IAC valve circuits with a ground. On a normally operating system, the test lamp should not flash while the IAC counts are incrementing.

1. Perform Diagnostic System Check - Engine Controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in appropriate 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 1700 RPM, then to 600 RPM. Then to 1700 RPM. Exit RPM control function. Did the engine speed stabilize within specifications during the above test? See «RPM VARIATION LIMITS»(/chevrolet/impala/viii-1999-2006/remont/testing-diagnostics/#engine-control-system-testing-engine-component-testing) table. If yes, see «DIAGNOSTIC AIDS»(/chevrolet/impala/viii-1999-2006/remont/testing-diagnostics/#engine-control-system-testing-engine-component-testing) . If no, go to next step.
3. Turn ignition off. Disconnect IAC valve harness connector. 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 1700 RPM is reached. Return engine RPM to desired idle as indicated on scan tool data list. Did the engine speed steadily decrease to near 600 RPM and steadily increase to near 1700 RPM when the IAC valve was commanded in and out? If yes, go to step 5 . If no, go to next step.
4. Did you observe an excessively high idle condition that could not be controlled with the IAC motor driver during the last test? If yes, go to step 11 . If no, 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. Did the test lamp remain ON, never flashing, while the IAC counts where incrementing at any of the IAC valve circuits during the above test? If yes, go to step 10 . If no, go to next step.
6. Did the test lamp remain OFF, never flashing, while the IAC counts where incrementing at any of the IAC valve circuits during the above test? If yes, go to step 9 . If no, go to next step.
7. Using Connector Test Adapter 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. Did the test lamp stay illuminated, never flashing, while the IAC counts where incrementing during the above test? If yes, go to next step. If no, go to step 17 .
8. Check for poor connection at IAC valve harness connector. Did you find and correct the condition? If yes, go to step 18 . If no, go to step 13 .
9. Turn ignition off. Disconnect PCM harness connectors. With a DMM, test the circuit where the test lamp remained off for the following: An open circuit. A short to ground. A short to another IAC valve circuit. Did you find and correct the condition? If yes, go to step 18 . If no, go to step 13 .
10. Turn ignition on. With a DMM, test the circuit where the test lamp remained illuminated for the following: A short to voltage. A short to another IAC valve circuit. Did you find and correct the condition? If yes, go to step 18 . If no, 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. Did you find and correct the condition? If yes, go to step 18 . If no, go to step 15 .
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. Did you find and correct the condition? If yes, go to step 18 . If no, go to step 15 .
13. Check for poor PCM harness connections. Did you find and correct the condition? If yes, go to step 18 . If no, go to next step.
14. Disconnect the PCM harness connectors. With a DMM, test all IAC valve circuits for high resistance. Did you find and correct the condition? If yes, go to step 18 . If no, go to step 17 .
15. Check for poor IAC valve harness connection. Did you find and correct the condition? If yes, go to step 18 . If no, go to next step.
16. Replace IAC valve. After repairs, go to step 18 .
17. Replace PCM. See POWERTRAIN CONTROL MODULE under COMPUTERIZED ENGINE CONTROLS in appropriate REMOVAL, OVERHAUL & INSTALLATION article. Program (flash) PCM with correct vehicle software and calibration. See POWERTRAIN CONTROL MODULE REPROGRAMMING under PROGRAMMING in appropriate SELF-DIAGNOSTICS article. After repairs, go to next step.
18. Reconnect any disconnected components. Use the scan tool to clear any DTCs that may have set. Turn OFF the ignition for 30 seconds. Operate the vehicle within conditions to verify the repair. Did you verify the repair? If yes, go to next step. If no, go to step 2 .
19. With a scan tool, observe the stored information in Capture Info. Does the scan tool display any DTCs that you have not diagnosed? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS in appropriate SELF-DIAGNOSTICS article. If no, system is okay.

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.

RPM VARIATION LIMITS

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.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 1 The System Check must be performed before proceeding with this diagnostic test. Failure to perform the System Check will result in misdiagnosis.
2. 3 This step tests the AF ECM fuses for opens and also tests the voltage supply to the fuses.
3. 5 This step tests the battery positive and switched ignition voltage circuits to the AF ECM.
4. 6 This step tests the AF ECM ground circuits.
5. 7 This step inspects for proper operation of the FIL. If the FIL illuminates then the ignition relay is ON.
6. 9 This step inspects the ignition relays ability to turn OFF.
7. 12 This step tests the Ignition Relay coils ground circuit. If the test lamp illuminates then the Ignition relay must be faulty.
8. 13 This step indicates the components or circuits that may have caused a fuse to blow. Some components may require they be turned ON in order to blow the fuse. An example would be depressing the fuel gauge select switch in order to test the select switch circuit for a short.

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, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-140667-S19215153262002052400000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 2.2L CAVALIER - 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 43) 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 Module (AF ECM) connectors. AF ECM is located behind left front fascia, below headlight. Turn ignition on. Using a test light connected to ground, probe AF ECM Blue connector C001 terminals No. 13 (Pink wire), No. 15 (Pink wire) and No. 16 (Orange wire). (Scheme 45) 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 ECM Clear/White connector C002 terminals No. 21, 22, 23 and 24. (Scheme 46) 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 41) If test light illuminates, go to FUEL INDICATOR LIGHT INOPERATIVE (CNG) under SYSTEM TESTS in appropriate ANALOG INSTRUMENT PANELS 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 41) 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, see «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-140667-S19215153262002052400000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 2.2L CAVALIER - 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 41) 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 ECM or AF ECM battery voltage supply circuit. For blown PCM fuse, check for the following conditions: Shorted ignition relay coil or circuit. Shorted AF ECM or AF ECM 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 ECM 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 ECM 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 ECM connectors. Repair as necessary. After repairs, go to step 22. If connections are okay, go to next step.
21. Replace AF ECM. See «ALTERNATE FUEL ENGINE CONTROL MODULE»(ref-150258-S32258339112002110700000) under COMPUTERIZED ENGINE CONTROLS in REMOVAL, OVERHAUL & INSTALLATION - CAVALIER & SUNFIRE article. Program (flash) AF ECM with correct vehicle software and calibration. See «ALTERNATE FUEL ENGINE CONTROL MODULE»(ref-140667-S13949165432002052400000) under PROGRAMMING in SELF-DIAGNOSTICS - 2.2L CAVALIER - 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 ECM 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, see DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in appropriate SELF-DIAGNOSTICS article.

Circuit Description

There are 2 separate ignition module assemblies, one for each bank of cylinders. Each assembly contains an ignition control (IC) module and 4 ignition coils. Each IC module consists of the following circuits

1. The ignition 1 voltage
2. A ground
3. The IC timing low reference
4. The IC control circuits for cylinders 1-8

Each ignition coil connects directly to its spark plug via a short boot. The IC control circuits transmit timing pulses from the powertrain control (PCM) module to the IC modules, which trigger the coils to fire the plugs in the correct sequence. The PCM monitors each IC control circuit for improper voltage levels.

When servicing the ignition system components, use the following recommended procedures

1. If a boot remains attached to a coil or to a spark plug, twist the boot prior to removal.
2. Inspect the boot for a missing or damaged internal spring.
3. Do not re-install any component that has visible signs of damage.
4. Install the boots onto the coils until the boots are bottomed out. Then install the assembly onto the spark plugs. If this is not possible due to space limitations, start the boots onto the spark plugs and then install the coil assembly as straight down onto the plugs as possible.
5. Ensure that the boots are installed right side up.
6. Lift the module beauty cover at the end opposite the module in order to remove.
7. Repair a torn perimeter seal with room temperature vulcanizing (RTV) sealant.
8. Adhere to the torque specifications when installing the coil cassette to the cam cover and the ignition module to the coil cassette.

A suspected ignition system misfire may actually be a condition other than the secondary ignition system. Verify proper operation of the following items

1. The fuel system Fuel Injector Balance Test with Special Tool or Fuel Injector Balance Test with Tech 2 Fuel Injector Coil Test.
2. Engine Mechanical Test for base engine conditions that could produce an engine misfire. Refer to «SYMPTOMS - ENGINE MECHANICAL»(ref-153484-S15373770172005041500000) in Engine Mechanical-4.0L.

The numbers below refer to the step numbers on the diagnostic table.

7. An ignition coil, boots, or spark plugs may misfire only when moisture is present. Although difficult to test on this engine, selectively wetting down parts of the system and monitoring for misfire may isolate an intermittent condition. If moisture is present in the spark plug/ignition coil cavity of the cam cover, inspect the perimeter seal for damage. Repair any tears in the perimeter seal with an RTV sealant.

8. The J 26792 Spark Tester (ST 125) places a higher load on the secondary ignition than a normal spark plug.

13. Use the correct adaptor harness when connecting the Ignition Module Tester. Using an adaptor harness for a different engine application will result in incorrect tool operation.

The green Power LED should come on any time the ignition module tester is connected and the ignition switch is in the run position. This LED indicates that J 43298 Ignition Module Tester is receiving adequate power and ground to perform the test. The Test button is used as an LED check for the 4 red LEDs. In order to use this function, connect the tool, turn the ignition switch to run, then momentarily press the Test button. All 4 red LEDs should come on brightly. Then crank the vehicle. If the 4 red LEDs flash, this confirms proper operation of the primary ignition system, including the PCM, the wiring, the connections, and the ignition control module (ICM). The ignition module tester may get hot during actual testing. This is because the tester is attempting to simulate the load of the ignition coils primary windings.

If the LEDs flash, the module output drivers are operating. If one or more LEDs are inoperative, and no individual IC Circuit (DTC P0351-P0358) Group, or IC Circuit Group (DTC P1359 and/or P1360) DTCs are set, replace the module.

Scheme 47

Scheme 48

Scheme 49

Scheme 50

Scheme 51

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 (Except Saturn)

1. Remove the pre-catalyst HO2S sensor. Install the Exhaust Back Pressure Gauge (J 35314-A) in place of the HO2S sensor. Start and run the engine. Increase and monitor the engine speed at specified RPM. See «EXHAUST BACKPRESSURE SPECIFICATIONS»(/chevrolet/impala/viii-1999-2006/remont/testing-diagnostics/#engine-control-system-testing-engine-component-testing) table. Observe the exhaust system back pressure reading on the gauge. Does the reading exceed the specified value? If yes, go to next step. If no, go to step 6 .
2. Turn the engine off and place the ignition in the lock position. Remove the J 35314-A. Install the pre-catalyst HO2S sensor. Remove the post-catalyst HO2S sensor. Install the J 35314-A in place of the post HO2S sensor. Start and run the engine. Increase and monitor the engine at specified RPM. See «EXHAUST BACKPRESSURE SPECIFICATIONS»(/chevrolet/impala/viii-1999-2006/remont/testing-diagnostics/#engine-control-system-testing-engine-component-testing) table. Observe the exhaust system back pressure reading on the gauge. Does the reading exceed the specified value? If yes, go to next step. If no, go to step 4 .
3. Inspect the exhaust system for the following conditions: Damage in the exhaust pipe. Debris in the exhaust pipe. Muffler or resonator internal failure. Two-layer exhaust pipe separation. After repairs, go to step 5 .
4. Replace the catalytic converter. After repairs, go to next step.
5. Remove the J 35314-A. Install the post-catalyst HO2S sensor. Clear any codes. Road test the vehicle in order to verify the repair. Did you find and correct the condition? If yes, system is okay. If no, go to step 1 .
6. Remove the J 35314-A. Install the pre-catalyst HO2S sensor. Clear any codes. Road test the vehicle in order to verify the repair. Did you find and correct the condition? If yes, system is okay. If no, go to step 1 .

EXHAUST BACKPRESSURE SPECIFICATIONS

Exhaust System Check - Parked (Saturn)

1. Remove oxygen sensor.
2. Insert Exhaust Back Pressure Adapter (SA9306E) into exhaust manifold. The thread designation is M18 x 1.50.
3. Connect Gauge Bar Set (SA9127E), 0-60 in. H2O (0-15 kPa) gauge to back pressure adapter.
4. With engine at normal operating temperature, observe exhaust back pressure at 4000 RPM.
5. The exhaust back pressure must be less than 20.13 in. H2O (5.0 kPa).

Exhaust System Check - Road Test (Saturn)

1. Remove heated oxygen sensor. Use 0-100 psi (0-690 kPa) gauge and appropriate hoses in Service Gauge Bar Kit (SA9127E).
2. Install Exhaust Back Pressure Adapter (SA9306E) into exhaust manifold. The thread designation is M18 x 1.50.
3. Connect gauge bar set SA9127E, 0-100 psi (0-861 kPa) gauge.
4. With engine at normal operating temperature, perform a 15 MPH (24 km/h) road test. Automatic transaxles should be in "D" and manual transaxles in "3rd" gear. Maximum exhaust back pressure readings are taken during short wide open throttle accelerations.
5. The maximum exhaust back pressure during wide open throttle accelerations must be less than 7.25 psi (50 kPa). If exhaust pressure exceeds specification, inspect for a dented or collapsed exhaust pipe. It may be necessary to disconnect exhaust pipe before or behind converter and repeat step 4 . If removing muffler does not lower back pressure, disconnect three way catalytic converter from exhaust manifold pipe and repeat test.
6. Replace any part of exhaust system found to be damaged.
7. Install anti-seize on heated oxygen sensor's threads and install sensor. It may be necessary to disconnect negative battery terminal in order to clear any codes set while operating engine with heated oxygen sensor removed or disconnected.

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

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.

Inspection Procedure

Note. Use the EVAP Pressure/Purge Diagnostic Station (J 41413) in order to provide a clean, dry, low pressure gas source. Do not substitute any other pressurized gas source. Damage may result to the EVAP system. Turn OFF the ignition. Remove the EVAP canister purge valve. Lightly tap the EVAP canister purge valve on a hard surface. Inspect for carbon particles exiting either of the vacuum ports. If no carbon particles were detected, but a blockage was detected during a diagnostic procedure. Install the original EVAP canister purge valve and continue with the cleaning procedure. If carbon particles are found during the inspection procedure. Replace the EVAP canister purge valve and continue with the cleaning procedure. If a diagnostic procedure directed you to replace the EVAP canister purge valve and no carbon particles were detected, replace the EVAP canister purge valve and return to diagnostic procedure.

Cleaning Procedure

1. Raise the vehicle.
2. Remove the EVAP canister.
3. Turn OFF the main valve on the J 41413.
4. Disconnect the hose from the diagnostic station pressure regulator.
5. Using a section of vacuum hose, connect one end onto the diagnostic station pressure regulator.
6. Connect the other end of the vacuum hose to the canister side of the purge pipe.
7. Turn ON the main nitrogen cylinder valve and continue to discharge nitrogen for 15 seconds.
8. If the nitrogen does not dislodge the carbon particles, replace the purge pipe.
9. Return the EVAP pressure/purge diagnostic station to the original condition of the station.
10. Install a new EVAP canister.
11. Lower the vehicle.
12. Install a new EVAP canister purge valve.
13. Return to the published service procedure.

The fuel tank leak test is used to locate any fuel or fuel vapor escaping the fuel tank area. Fuel vapors escaping above the fuel level will be detected when the Evaporative (EVAP) emission diagnostics complete one test cycle. The Malfunction Indicator Lamp (MIL) will illuminate after the EVAP diagnostics complete two test cycles.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 1 Perform this procedure in order to determine that no EVAP diagnostic DTC is present.
2. 3 This test is to locate fuel leakage in the fuel lines.
3. 4 This tests for fuel leaks below the fuel tank fuel level.
4. 5 This test is to locate fuel vapors escaping above the fuel level in the fuel tank.

1. Perform Diagnostic System Check - Engine Controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in appropriate SELF-DIAGNOSTICS article.
2. Raise the vehicle. Inspect the fuel tank and fuel pipes for damage or external leaks. Did you find fuel leaking from the fuel tank? If yes, go to step 7 . If no, go to next step.
3. Turn ON the ignition, with the engine OFF. With a scan tool, command the fuel pump ON. Inspect for fuel leaking from the fuel pipes. Did fuel leak from the fuel pipes? If yes, go to step 8 . If no, go to next step.
4. Install the Fuel Tank Cap Adapter (J 41415-40). Connect the EVAP Pressure/Purge Diagnostic Station (J 41413) to the fuel tank cap adapter. With a scan tool, seal the EVAP system. DO NOT exceed 15 in. H2O. With the EVAP pressure/purge diagnostic station, pressurize the fuel tank. Did fuel leak from the fuel tank? If yes, go to step 7 . If no, go to next step.
5. With the EVAP pressure/purge diagnostic station, maintain pressure in the fuel tank. The fuel tank may need to be partially lowered. With the Ultrasonic Leak Detector (J 41416), test for leaks above the fuel level in the following locations. The fuel tank, fill limiter vent valve, pressure relief valve and rollover valves. The fuel sender housing and fuel sender seal. The Fuel Tank Pressure (FTP) sensor seal. The EVAP vapor pipes. The fuel fill pipe and hose. Did you locate a fuel leak? If yes, go to next step. If no, see «DIAGNOSTIC AIDS»(/chevrolet/impala/viii-1999-2006/remont/testing-diagnostics/#engine-control-system-testing-engine-component-testing) .
6. Repair the system as necessary. After repairs, system is okay.
7. Replace the fuel tank. After repairs, system is okay.
8. Replace the leaking fuel pipe. After repairs, system is okay.

1. Operate the vehicle under the condition of the customers concern. Under high temperature conditions fuel vapors may increase to the point of EVAP canister vapor saturation. Fuel vapors would then be released into the atmosphere. Once the engine is running and EVAP purge is enabled, all fuel vapor release would be eliminated.
2. Test for fuel leaking in the fuel tank and the fuel feed and return pipes.
3. Test for fuel vapor leaks in the fuel tank, fill limiter vent valve and rollover valves, the fuel fill pipe, hose and fuel fill cap, the fuel sender housing and seal, the Fuel Tank Pressure (FTP) sensor seal and the EVAP vapor pipe.
4. Movement of the EVAP pipes or fuel pipes may help find an intermittent condition.

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 or AUTOMATIC 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 DIAGNOSIS 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 52)- (Scheme 58).

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

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

COMPONENT LOCATIONS (2.2L VIN 4 - CAVALIER - CNG)

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

COMPONENT LOCATIONS (2.2L VIN 4 - CAVALIER - CNG)

COMPONENT LOCATIONS (2.2L VIN F - ALERO & GRAND AM)

COMPONENT LOCATIONS (2.2L VIN F - ALERO & GRAND AM)

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 - 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)

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

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 - PARK AVENUE)

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

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 52

Scheme 53

Scheme 54

Scheme 55

Scheme 56

Scheme 57

Scheme 58

See also:
• FUEL SYSTEM PRESSURE RELIEF (SATURN)
• NO-START - ENGINE CRANKS OKAY (2.2L & 2.4L - ALERO, CAVALIER, GRAND AM & SUNFIRE)
• MODEL IDENTIFICATION
• COMPONENT LOCATIONS
• IDLE CONTROL SYSTEM
• FUEL PUMP RELAY