Engine Controls - System & Component Tests: Diagnosis Chevrolet Venture I

PCM OUTPUT DIAGNOSIS (2.2L - VIN 4)

1. Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. After performing OBD system check, go to next step.
2. Turn ignition on with engine off. Connect scan tool to Data Link Connector (DLC). If a No. 1 is displayed below any of the number output drivers, go to next step. If a No. 1 is not displayed below any of the number output drivers, go to step 4 .
3. Disconnect electrical connector from component related to malfunctioning circuit. If a No. 1 is still displayed below corresponding output driver, go to step 6 . If a No. 1 is not displayed below any of the number output drivers, go to step 9 .
4. Using scan tool, command output being checked while watching corresponding position for that circuit. If that circuits position does not change to a No. 1, go to next step. If that circuits position changes to a No. 1, go to step 7 .
5. If component or function does not operate when commanded, go to step 9 . If component or function operates when commanded, go to step 11 .
6. Turn ignition off. Check for an open, short to voltage or short to ground in any corresponding circuit that indicated a No. 1 below output driver. Repair component or component circuit as necessary and go to step 11 . If circuits are okay, go to step 10 .
7. Disconnect electrical connector from component related to malfunctioning circuit. Using scan tool, command output being checked while watching corresponding position for that circuit. If a No. 1 is still displayed below corresponding output driver, go to next step. If a No. 1 is not displayed below any of the number output drivers, go to step 9 .
8. Turn ignition off. Check for an open, short to voltage or short to ground in any corresponding circuit that indicated a No. 1 below output driver. Repair component or component circuit as necessary and go to step 11 . If circuits are okay, go to step 10 .
9. Diagnose and repair any component that malfunctioned when commanded with scan tool. After repairs, go to step 11 .
10. Replace PCM. Program replacement PCM using required equipment. After repairs, go to next step.
11. Start engine and operate vehicle under condition under which original symptom was noted. If system does not operate properly, go to step 2 . If system operates properly, see «DIAGNOSTIC AIDS»(ref-9314-S04508269662000101700000) .

Diagnostic Aids

Scan tool has the ability to command certain components and functions ON and OFF. If a component or function does not have this capability, operate vehicle during normal function criteria to check for an open or shorted circuit. An open or short to ground will appear in the open positions of the scan tool only when it is not commanded by the PCM or scan tool. A short to voltage will appear in the short positions on the scan tool only while the component is being commanded by the PCM or scan tool.

Fuel Injector Circuit Diagnosis (Except 2.2L & 3.4L)

Note. Fuel injector circuit diagnosis test information for 2.2L (VIN 4) and 3.4L engines is not available from manufacturer.

1. Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. Go to next step.
2. Disconnect fuel injector harness connectors at intake manifold. Using a test light connected to ground, probe appropriate injector ignition feed circuits at fuel injector harness connector. Turn ignition on with engine off. If test light illuminates on both circuits, go to step 6 . If test light does not illuminate on both circuits, go to next step.
3. If test light illuminates on only one injector ignition feed circuit, go to step 5 . If test light does not illuminate on only one injector ignition feed circuit, go to next step.
4. Check injector fuse. If fuse is blown, go to step 10 . If fuse is okay, go to step 11 .
5. Check for an open in appropriate injector feed circuit between PCM and injector harness connector. If open exists, go to step 12 .
6. Connect Fuel Injector Test Light (J-34730-380) to fuel injector harness connectors (PCM side) one at a time. Crank engine while observing test light. If test light does not flash at each injector, go to next step. If test light flashes at each injector, perform injector coil test. See «INJECTOR COIL TEST (EXCEPT 2.2L & 3.4L)»(ref-9314-S12465350512000101700000) .
7. If fuel injector test light illuminates constantly while engine is being cranked, go to next step. If fuel injector test light does not illuminate constantly while engine is being cranked, go to step 9 .
8. Install fuel injector test light on affected circuit. Turn ignition off. Disconnect PCM harness connectors. Turn ignition on with engine off. If test light illuminates, go to step 13 . If test light does not illuminate, go to step 16 .
9. Check for an open in injector control circuit between PCM and injector harness connectors. If open exists, go to step 12 . If an open does not exist, go to step 14 .
10. Check for a short to ground in injector ignition feed circuit between PCM and injector harness connectors. If a short to ground exists, go to step 12 .
11. Repair open or short to ground on both injector ignition feed circuits. After repairs, go to step 17 .
12. Repair circuit as necessary. After repairs, go to step 17 .
13. Repair short to ground in injector control circuit between PCM and injector harness connectors. After repairs, go to step 17 .
14. Check PCM harness connectors for poor connections. If poor connection exists, go to next step. If poor connection does not exist, go to step 16 .
15. Repair terminal contact as necessary. After repairs, go to step 17 .
16. Replace PCM and reprogram PCM. Perform VTD password relearn procedure and crankshaft variation learn procedure. See COMPUTER RELEARN PROCEDURES article in GENERAL INFORMATION. After repairs, go to step 17 .
17. Using scan tool, clear DTCs. Attempt to start engine. If engine starts and continues to run, go to next step. If engine does not start and continue to run, go to step 2 .
18. Let engine idle until normal operating temperature is reached. Retrieve DTCs. If no DTCs are set, system is okay. If any DTCs are set, perform appropriate DTC test. See appropriate SELF-DIAGNOSTICS article.

Injector Balance Test (2.2L - VIN 4 & 3.4L)

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

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

1. Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. Go to next step.
2. If injector coil test has been performed, go to next step. If injector coil test has not been performed, see appropriate INJECTOR COIL TEST - ECT IS 50-95°F.
3. If engine coolant temperature is greater than 201°F (94°C), go to next step. If engine coolant temperature is less than 201°F (94°C), go to step 5 .
4. Allow engine to cool to less than 201°F (94°C). After engine cools to less than 201°F (94°C), go to next step.
5. Install fuel pressure gauge. Using scan tool, energize fuel pump. Place fuel pressure gauge bleed hose into container. Bleed air out of fuel pressure gauge. Using scan tool, energize fuel pump again. Wait for fuel pressure to build. Observe fuel pressure. If fuel pressure reading is 41-47 psi (2.9-3.3 kg/cm 2 ), go to next step. If fuel pressure reading is not within specification, perform fuel system diagnosis. See appropriate BASIC DIAGNOSTIC PROCEDURES article.
6. Turn fuel pump off. Observe fuel pressure gauge. If fuel pressure remains constant, go to next step. If fuel system does not remain constant, perform fuel system diagnosis. See appropriate BASIC DIAGNOSTIC PROCEDURES article.
7. Disconnect fuel injectors harness connector. Using appropriate fuel injector adapter, connect Fuel Injector Tester (J-39021) to fuel injector. Connect fuel injector tester power leads to appropriate battery terminals. Set amperage supply selector switch on fuel injector tester to Balance Test 0.5-2.5-amp position. Turn ignition on, and then off to pressurize system. Record fuel pressure reading after fuel pressure stabilizes (first reading). Energize injector by depressing PUSH TO START TEST button on injector tester and hold until fuel pressure gauge stabilizes. Record fuel pressure reading (second reading). Subtract first reading from second reading (this result is pressure drop value). Repeat procedure for each injector. Add pressure drop value for each injector together and divide total by total number of injectors. If any injector's drop value is greater or less than average drop value by 1.5 psi, replace faulty injector(s) as necessary. If no injector's drop value is greater or less than average drop value by 1.5 psi, repair by symptom. See appropriate TROUBLE SHOOTING - NO CODES article.

Injector Balance Test (Except 2.2L & 3.4L)

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

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

1. Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. Go to next step.
2. If engine coolant temperature is greater than 201°F (94°C), go to next step. If engine coolant temperature is less than 201°F (94°C), go to step 4 .
3. Allow engine to cool to less than 201°F (94°C). After engine cools to less than 201°F (94°C), go to next step.
4. Turn ignition off. Relieve fuel pressure. Install fuel pressure gauge. Turn ignition on with engine off. Install scan tool. Using scan tool, energize fuel pump. Place fuel pressure gauge bleed hose into container. Bleed air out of fuel pressure gauge. Using scan tool, energize fuel pump again. Wait for fuel pressure to build. Observe fuel pressure while fuel pump is running. If fuel pressure reading is 60-66 psi (4.2-4.6 kg/cm 2 ) on 4.3L, 5.0L and 5.7L, or 55-62 psi (4.0-4.4 kg/cm 2 ) on 4.8L, 5.3L, 6.0L and 7.4L, go to next step. If fuel pressure reading is not within specification, perform fuel system diagnosis. See appropriate BASIC DIAGNOSTIC PROCEDURES article.
5. After fuel pump stops, fuel pressure should slightly decrease. If fuel pressure remains constant within 55-60 psi (4.0-4.2 kg/cm 2 ) on 4.3L, 5.0L and 5.7L, or 48-52 psi (3.4-3.7 kg/cm 2 ) on 4.8L, 5.3L, 6.0L and 7.4L, go to next step. If fuel pressure reading is not within specification, perform fuel system diagnosis. See appropriate BASIC DIAGNOSTIC PROCEDURES article.
6. Turn ignition off. Turn ignition on with engine off. Using scan tool, select SPECIAL FUNCTIONS. Select FUEL SYSTEMS, and then INJECTOR BALANCE TEST. Select injector to be tested. Press enter, this will prime fuel pump. After fuel pressure stabilizes, record fuel pressure reading on fuel pressure gauge (first reading). Energize injector by depressing PULSE INJECTOR button on scan tool. Injector will be energized and fuel pressure will decrease. Record fuel pressure reading after fuel pressure stabilizes (second reading). Press enter on scan tool to return to SELECT INJECTOR. Repeat procedure for each injector. Subtract first reading from second reading for each injector (this result is pressure drop value). Add pressure drop value for each injector together and divide total by total number of injectors. If any injector's drop value is greater or less than average drop value by 1.5 psi, replace faulty injector(s) as necessary. If no injector's drop value is greater or less than average drop value by 1.5 psi, perform injector coil test. See «INJECTOR COIL TEST (EXCEPT 2.2L & 3.4L)»(ref-9314-S12465350512000101700000) .

Injector Coil Test (Except 2.2L & 3.4L)

1. Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. Go to next step.
2. Turn ignition off. Relieve fuel pressure. Connect Fuel Injector Tester (J-39021) to battery voltage. Connect Injector Switch Box (J-39021-210). Set amperage on fuel injector tester to 0.5 amp. Connect DVOM to fuel injector tester. Install scan tool and monitor engine coolant temperature. If coolant temperature is 50-95°F (10-35°C), go to step 4 . If coolant temperature is not as specified, go to next step.
3. Allow engine to warm or cool as necessary. If engine coolant temperature is now 50-95°F (10-35°C), go to next step.
4. Using fuel injector tester, press PUSH TO START TEST button and monitor DVOM reading. Repeat procedure for each injector. Voltage reading should be 5.44-7.53 volts. If voltage reading is as specified, go to next step. If voltage reading is not as specified, perform injector balance test. See «INJECTOR BALANCE TEST (EXCEPT 2.2L & 3.4L)»(ref-9314-S02106239072000101700000) .
5. Replace faulty injector nozzle and poppet assembly. After repairs, go to next step.
6. Using scan tool, clear DTCs. Start engine. If engine starts and continues to run, go to next step. If engine does not start, or starts and dies, go to step 2 .
7. Warm engine to normal operating temperature. Using scan tool, retrieve DTCs. If no DTC(s) are set, system is okay. If any DTC(s) are set, perform appropriate DTC(s) test. See appropriate SELF-DIAGNOSTICS article.

Injector Coil Test - ECT Is 50-95°F (2.2L - VIN 4)

1. Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. Go to next step.
2. Install scan tool. Using scan tool, check engine coolant temperature. If coolant temperature is 50-95°F (10-35°C), go to next step. If coolant temperature is not 50-95°F (10-35°C), perform injector coil test. See «INJECTOR COIL TEST - ECT IS NOT 50-95°F (2.2L - VIN 4)»(ref-9314-S27930313112000101700000) .
3. Turn ignition off. Relieve fuel pressure. Disconnect fuel injectors harness connector. Using appropriate fuel injector adapter, connect Fuel Injector Tester (J-39021) to fuel injector. Connect fuel injector tester power leads to appropriate battery terminals. Set amperage supply selector switch on fuel injector tester to Coil Test 2.5-amp position. Connect DVOM to injector tester. Depress PUSH TO START TEST button. Record lowest voltage reading within first second of test. Repeat procedure for each injector. If any injector has erratic voltage reading or reading not within 4.7-5.8 volts, go to next step. If no injector has erratic voltage reading or reading not within 4.7-5.8 volts, perform injector balance test. See «INJECTOR BALANCE TEST (2.2L - VIN 4 & 3.4L)»(ref-9314-S11861583122000101700000) .
4. Replace faulty injector(s). After repairs, perform injector balance test. See «INJECTOR BALANCE TEST (2.2L - VIN 4 & 3.4L)»(ref-9314-S11861583122000101700000) .

Injector Coil Test - ECT Is 50-95°F (3.4L)

1. Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. Go to next step.
2. Install scan tool. Using scan tool, check engine coolant temperature. If coolant temperature is 50-95°F (10-35°C), go to next step. If coolant temperature is not 50-95°F (10-35°C), perform injector coil test. See «INJECTOR COIL TEST - ECT IS NOT 50-95°F (3.4L)»(ref-9314-S27930313112000101700000) .
3. Turn ignition off. Relieve fuel pressure. Connect Fuel Injector Tester (J-39021), Injector Switch Box (J-39021-210) and Fuel Injector Test Harness (J-39021-306) to fuel injector connector. Set amperage on fuel injector tester to Coil Test 0.5 amp position. Connect DVOM to fuel injector tester. Select fuel injector using injector switch box. Depress PUSH TO START TEST button. Record lowest voltage reading within first second of test. Repeat procedure for each injector. If any injector has erratic voltage reading or reading not within 5.7-6.6 volts, go to next step. If no injector has erratic voltage reading or reading not within 5.7-6.6 volts, perform injector balance test. See «INJECTOR BALANCE TEST (2.2L - VIN 4 & 3.4L)»(ref-9314-S11861583122000101700000) .
4. Replace faulty injector(s). After repairs, perform injector balance test. See «INJECTOR BALANCE TEST (2.2L - VIN 4 & 3.4L)»(ref-9314-S11861583122000101700000) .

Injector Coil Test - ECT Is Not 50-95°F (2.2L - VIN 4)

1. Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. Go to next step.
2. Install scan tool. Using scan tool, check engine coolant temperature. If coolant temperature is not 50-95°F (10-35°C), go to next step. If coolant temperature is 50-95°F (10-35°C), perform injector coil test. See «INJECTOR COIL TEST - ECT IS 50-95°F (2.2L - VIN 4)»(ref-9314-S19058377832000101700000) .
3. Turn ignition off. Relieve fuel pressure. Disconnect fuel injectors harness connector. Using appropriate fuel injector adapter, connect Fuel Injector Tester (J-39021) to fuel injector. Connect fuel injector tester power leads to appropriate battery terminals. Set amperage supply selector switch on fuel injector tester to Coil Test 2.5-amp position. Connect DVOM to injector tester. Depress PUSH TO START TEST button. Record lowest voltage reading within first second of test. Record highest voltage reading other than those above 9.5 volts. Subtract any other voltage reading observed from highest voltage reading. Repeat procedure for each injector. If difference is greater than 4.7-5.8 volts, go to next step. If difference is less than 4.7-5.8 volts, perform injector balance test. See «INJECTOR BALANCE TEST (2.2L - VIN 4 & 3.4L)»(ref-9314-S11861583122000101700000) .
4. Replace any injector(s) showing an initial reading greater than 9.5 volts, erratic reading or difference is greater than 0.6 volt. After repairs, perform injector balance test. See «INJECTOR BALANCE TEST (2.2L - VIN 4 & 3.4L)»(ref-9314-S11861583122000101700000) .

Injector Coil Test - ECT Is Not 50-95°F (3.4L)

1. Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. Go to next step.
2. Install scan tool. Using scan tool, check engine coolant temperature. If coolant temperature is not 50-95°F (10-35°C), go to next step. If coolant temperature is 50-95°F (10-35°C), perform injector coil test. See «INJECTOR COIL TEST - ECT IS 50-95°F (3.4L)»(ref-9314-S04927570122000101700000) .
3. Turn ignition off. Relieve fuel pressure. Connect Fuel Injector Tester (J-39021), Injector Switch Box (J-39021-210) and Fuel Injector Test Harness (J-39021-306) to fuel injector connector. Set amperage on fuel injector tester to Coil Test 0.5 amp position. Connect DVOM to fuel injector tester. Select fuel injector using injector switch box. Depress PUSH TO START TEST button. Record lowest voltage reading within first second of test. Record highest voltage reading other than those above 9.5 volts. Subtract any other voltage reading observed from highest voltage reading. Repeat procedure for each injector. If difference is greater than 0.6 volt, go to next step. If difference is less than 0.6 volt, perform injector balance test. See «INJECTOR BALANCE TEST (2.2L - VIN 4 & 3.4L)»(ref-9314-S11861583122000101700000) .
4. Replace any injector(s) showing an initial reading greater than 9.5 volts, erratic reading or difference is greater than 0.6 volt. After repairs, perform injector balance test. See «INJECTOR BALANCE TEST (2.2L - VIN 4 & 3.4L)»(ref-9314-S11861583122000101700000) .

PRELIMINARY GLOW PLUG DIAGNOSIS

Note. Glow plug on-and-off times vary with engine temperature, system voltage and/or ambient temperature. Lower temperatures cause longer duration of cycling.

1. If system does not operate as described in «NORMAL GLOW PLUG CIRCUIT OPERATION»(ref-9314-S06011242702000101700000) , ensure glow plug system is correctly installed. Ensure all connectors are properly attached, clean and tight. Inspect engine harness ground connection. Ensure nuts securing glow plug relay to engine are tightened to 31 ft. lbs. (42 N.m). Ensure connector is fully seated in relay.
2. Ensure glow plug relay copper stud upper nuts are tightened to 44 INCH lbs. (5 N.m). DO NOT overtighten nuts. Inspect WAIT TO START light on instrument cluster for tight connection and proper operation.

FUEL HEATER DIAGNOSIS

1. If water in fuel light is operating properly, go to next step. If water in fuel light is not operating properly, perform water in fuel light diagnosis. See «WATER-IN-FUEL LIGHT DIAGNOSIS»(ref-9314-S32734898652000101700000) .
2. Disconnect fuel heater harness connector and remove heater from filter housing. With fuel heater temperature greater than 50°F (10°C), apply battery voltage to fuel heater terminal "C" (Pink wire) and ground fuel heater terminal "A" (Black wire). Observe heater element. If heat does not exist, go to next step. If heat exists, go to step 4 .
3. Cool fuel heater to less than 46°F (8°C) and wet heating element with fuel. Connect fuel heater to battery voltage and ground as in step 2 . Observe heater element. If heat does not exist, go to next step. If heat exists, go to step 5 .
4. Replace fuel heater. After repairs, go to next step.
5. Operate vehicle under conditions when problem was noted. If system does not operate properly, go to step 1 .

WATER-IN-FUEL LIGHT DIAGNOSIS

1. Turn ignition on with engine off. If WATER IN FUEL light does not illuminate, go to next step. If WATER IN FUEL light illuminates briefly, go to step 5.
2. Disconnect water-in-fuel sensor harness connector. Ensure ignition is on with engine off. Using an unpowered test light connected to ground, probe ignition feed circuit (Pink wire) at water-in-fuel sensor harness connector. (Scheme 6) If test light illuminates, go to next step. If test light does not illuminate, go to step 6.
3. Connect test light between ignition feed circuit (Pink wire) and ground circuit (Black wire) at water-in-fuel sensor harness connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 8.
4. Using test light connected to ground, probe indicator light control circuit (Yellow/Black wire) at water-in-fuel sensor harness connector. (Scheme 6) If test light illuminates, go to step 11. If test light does not illuminate, go to step 10.
5. Operate vehicle under conditions when problem was noted. If system does not operate properly, go to step 2.
6. Check for open in ignition feed circuit (Pink wire) between underhood fuse/relay center and water-in-fuel sensor. If problem exists, repair as necessary and go to step 12. If problem does not exist, go to next step.
7. Check ignition feed circuit (Pink wire) for poor connection at water-in-fuel sensor. If problem exists, repair as necessary and go to step 12. If problem does not exist, go to step 11.
8. Check for open in ground circuit (Black wire) between water-in-fuel sensor and ground connection. If problem exists, repair as necessary and go to step 12. If problem does not exist, go to next step.
9. Check ground circuit (Black wire) for poor connection at water-in-fuel sensor. If problem exists, repair as necessary and go to step 12. If problem does not exist, go to step 11.
10. Repair open in indicator light control circuit (Yellow/Black wire) between instrument cluster and water-in-fuel sensor. After repairs, go to step 12.
11. Replace water-in-fuel sensor. After repairs, go to next step.
12. Operate vehicle under conditions when problem was noted. If system does not operate properly, go to step 1.

Scheme 6

GLOW PLUG SYSTEM DIAGNOSIS

1. Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. Go to next step.
2. Retrieve DTCs. If DTC P0117, P0118 and/or P0380 is not set, go to next step. If DTC P0117, P0118 and/or P0380 is set, perform appropriate DTC test. See appropriate SELF-DIAGNOSTICS article.
3. Turn ignition off. Disconnect all glow plug harness connectors. Using a test light connected to battery voltage, probe each glow plug spade terminal at glow plugs. If test light illuminates at each glow plug, go to next step. If test light does not illuminate at each glow plug, go to step 9 .
4. Ensure all glow plug harness connectors are still disconnected. Turn ignition on with engine off. Using scan tool, command glow plugs on. Using a test light connected to ground, probe each glow plug harness connector terminal. If test light illuminates at each glow plug harness connector, go to next step. If test light does not illuminate at each glow plug harness connector, go to step 10 .
5. Using scan tool, command glow plugs off. Using a test light connected to ground, probe each glow plug harness connector terminal. If test light illuminates at any glow plug harness connector, go to next step. If test light does not illuminate at any glow plug harness connector, go to step 11 .
6. Remove glow plug relay. Using scan tool, command glow plugs off. Using a test light connected to ground, probe each glow plug harness connector terminal. If test light illuminates at any glow plug harness connector, go to next step. If test light does not illuminate at any glow plug harness connector, go to step 8 .
7. Repair short to voltage in glow plug output circuit or glow plug signal circuit. After repairs, go to step 11 .
8. Replace glow plug relay. After repairs, go to step 11 .
9. Replace glow plugs that did not illuminate test light. After repairs, go to step 11 .
10. Repair open in glow plug circuit(s) that did not illuminate test light. After repairs, go to next step.
11. Operate vehicle under conditions when problem was noted. If system does not operate properly, go to step 1 .

INJECTION PUMP HOUSING LEAKAGE TEST

1. Remove injection pump and drain all fuel. Connect an air supply line to fuel inlet fitting. Ensure air supply is clean and dry. Seal off return line fitting. Completely immerse pump assembly in a container of clean test oil.
2. Apply 20 psi (1.4 kg/cm 2 ) to pump. Leave pump immersed for 10 minutes to allow trapped air to escape. Watch for leaks after 10 minutes. If no leaks are observed after 10 minutes, reduce air pressure to 2 psi (.14 kg/cm 2 ) for 30 seconds.
3. If there are still no leaks, increase pressure to 20 psi (1.4 kg/cm 2 ) again. If no leaks are observed, pump is okay. If leaks are noticed, replace pump.

Test Preparation

1. Remove injector nozzles from engine. Clean carbon from tip area of nozzle with soft brass wire brush. DO NOT use steel brush or motorized brush to clean nozzle tip. Damage to nozzle tip may result.
2. Connect injector nozzle to injection nozzle tester. Place clear plastic tubing on both fuel return fittings to prevent bleed-off from being confused with leaks. Close tester shutoff valve to pressure gauge.
3. Fill tester with test fluid. Fill and flush nozzle assembly with test fluid by operating tester lever briskly and repeatedly. This purges air from injector nozzle and coats all parts with test fluid.

Opening Pressure Test

1. Open tester shutoff valve 1/4 turn from closed position. Slowly depress tester lever and observe gauge. Note pressure at which needle of pressure gauge stops. Some injector nozzles may pop while other injector nozzles may drip (this is not a leak).
2. Injector opening pressure should not fall to less than 1500 psi (105 kg/cm 2 ). Replace any injector nozzle where measurement does not meet lowest acceptable pressure. Release tester pressure.

Leakage Test

1. Open tester shutoff valve 3/4 to 1 3/4 turns from closed position. Blow dry injector nozzle tip. Slowly depress tester lever until pressure gauge reads 1400 psi (98 kg/cm 2 ). Maintain pressure for 10 seconds and observe injector nozzle tip.
2. A drop may form on end of injector nozzle, but should not fall off within a 10 second period. Replace injector nozzle if a drop of test fluid falls from tip during 10 second period. (Scheme 7) Release tester pressure.

Scheme 7

Chatter Test

Chatter for new and used injector nozzles may vary. With some used injector nozzles, chatter is difficult to detect during slow actuation of tester lever. Some injector nozzles may chatter louder than others. As long as there is audible chatter, injector nozzle is acceptable.

1. Close tester shutoff lever at pressure gauge. Slowly depress lever and note whether chatter is heard. If no chatter is heard, increase speed of lever movement until it reaches a point at which injector nozzle chatters.
2. At fast lever movement, injector nozzle may emit a "hissing" or "squealing" sound rather than normal chatter. This is acceptable. These sounds indicate that injector nozzle needle moves freely and injector nozzle seat, guide and pintle have no mechanical defects. Replace any injector nozzle assembly that does not chatter.

Spray Pattern Test

The injector nozzles used with this system have several features that make pattern testing difficult. These features include longer nozzle overlap, greater pintle-to-body clearances and an internal wave washer between injector nozzle nut and injector. Typical injector nozzle tester cannot deliver fuel with sufficient velocity to obtain proper spray patterns. DO NOT replace injector nozzle(s) based on spray pattern.

Circuit Description

The Alternative Fuel Engine Control Unit (AF ECU) controls fuel system when vehicle is operating on CNG. CNG is stored in a tank at pressures up to 3600 psi. A High Pressure Lock-Off (HPL) in the tank and a Low Pressure Lock-Off (LPL) in fuel line prevent fuel flow. When ignition is turned on, AF ECU commands HPL open for one second to charge fuel system, and allows Fuel Pressure Sensor (FPS) to monitor tank pressure. When engine is cranking or running, AF ECU opens both HPL and LPL. System pressure is reduced at three stages. Fuel tank and system before high pressure regulator is at up to 3600 psi. Intermediate section pressure after high pressure regulator is 130-200 psi. Fuel pressure is reduced to 4-6 psi inside low pressure regulator. Secondary stage of low pressure regulator reduces pressure to 4.5-7 in. Hg. Fuel exits low pressure regulator and enters Gas Mass Sensor/Mixture Control Valve (GMS/MCV).

Diagnostic Procedure

Note. If DTC sets causing gasoline operation, check pressure only before DTC sets. If vehicle will not idle on CNG, check cranking pressure. A rhythmic pressure fluctuation of 10-20 psi is normal.

1. Perform OBD system check. See ON BOARD DIAGNOSTIC (OBD) SYSTEM CHECK under SELF-DIAGNOSTIC SYSTEM in appropriate SELF-DIAGNOSTICS article. If any DTCs except P1202 exist, perform appropriate test. See appropriate SELF-DIAGNOSTICS article.
2. Connect vehicle to filling station. Ensure fuel tank is at least 1/3 full (1200 psi). Go to next step.
3. Relieve fuel system pressure. See BASIC FUEL SYSTEM CHECKS (CNG) in appropriate BASIC DIAGNOSTIC PROCEDURES article. Remove pressure relief device from High Pressure Regulator (HPR). Install electronic pressure gauge adapter (J-39970-UPD) in HPR. Connect pressure gauge to adapter. Connect DVOM to pressure gauge. Monitor fuel pressure. Start engine. Warm engine to operating temperature. Apply parking brake. Firmly depress brake. Shift vehicle into Drive. Depress throttle to at least 80 percent for 10 seconds. Allow engine to idle for 2 minutes to cool transmission. If fuel pressure does not remain 130-220 psi during testing, go to next step. If fuel pressure remains 130-220 psi during testing, go to step 5 .
4. If pressure is more than 220 psi, go to step 19 If pressure is less than 130 psi, go to step 10 .
5. Turn ignition off. Remove primary test port plug from Low Pressure Regulator (LPR). Install adapter and 0-15 psi pressure gauge from Test Kit (J-42580). Monitor fuel pressure. Start engine. Warm engine to operating temperature. Apply parking brake. Firmly depress brake. Shift vehicle into Drive. Depress throttle to at least 80 percent for 10 seconds. Allow engine to idle for 2 minutes to cool transmission. If fuel pressure does not remain 4-6 psi during testing, go to next step. If fuel pressure remains 4-6 psi during testing, go to step 7 .
6. If pressure is more than 6 psi, go to step 18 . If pressure is less than 4 psi, go to step 15 .
7. Turn ignition off. Remove gauge and adapter from primary test port. Install plug, using Teflon® sealant, not tape. Remove secondary test port plug from LPR and install adapter. Some oil may drain from test port. Connect Slack Tube Manometer (J-7333-6) to adapter. Keep vent port of manometer closed until after engine starts. Start engine. Warm engine to operating temperature. Apply parking brake. Firmly depress brake. Shift vehicle into Drive. Depress throttle to at least 80 percent for 10 seconds. Allow engine to idle for 2 minutes to cool transmission. If fuel pressure does not remain 4.5-7.0 in Hg during testing, go to next step. If fuel pressure remains 4.5-7.0 in Hg during testing, go to step 9 .
8. Check for loose clamps, damage, cracks or worn components. Check vapor hose between LPR and GMS/MCV. Check hose between GMS/MCV and Gas Distribution Adapter (GDA). Check for smooth, free operation of butterfly valve in GMS/MCV. If no problem is found, go to step 18 . If any problem is found, repair as necessary. After repairs, go to step 22 .
9. Turn ignition off. Remove manometer and adapter from secondary test port. Install plug, using Teflon® sealant, not tape. With DVOM from step 3 and a helper in vehicle, test drive vehicle. Check pressure with vehicle in gear at idle. Check pressure when accelerating with throttle depressed at least 80 percent. If fuel pressure does not remain 130-220 psi during testing, go to step 19 . If fuel pressure remains 130-220 psi during testing, go to step 22 .
10. Relieve fuel system pressure. See BASIC FUEL SYSTEM CHECKS (CNG) in appropriate BASIC DIAGNOSTIC PROCEDURES article. Replace filter in High Pressure Regulator (HPR). Monitor fuel pressure. Start engine. Warm engine to operating temperature. Apply parking brake. Firmly depress brake. Shift vehicle into Drive. Depress throttle to at least 80 percent for 10 seconds. Allow engine to idle for 2 minutes to cool transmission. If fuel pressure does not remain 130-220 psi during testing, go to next step. If fuel pressure remains 130-220 psi during testing, go to step 22 .
11. Turn ignition off. Remove fuel tank cover. Disconnect 2-pin HPL connector C313. Connect test light between harness connector terminals. Crank engine. If test light illuminates, go to next step. If test light does not illuminate, check relay. See «LOCK-OFF RELAY»(ref-9314-S38627876982000102600000) .
12. Ensure manual lock-down screw on HPL manual shut-off fitting is open by turning Allen screw fully counter-clockwise. If shut off valve was open, go to next step. If shut off valve was not fully open, open valve and go to step 22 .
13. Turn ignition off. Connect HPL connector. AF ECU should energize HPL for one second when ignition is turned on. Check HPL operation while turning ignition on. If HPL is okay, go to next step. If HPL does not operate, go to step 20 .
14. Check for kinks, bends, damage and obstruction in fuel line between HPL and HPR. If no problem is found, go to step 19 . If any problem is found, repair as necessary. After repairs, go to step 22 .
15. Turn ignition off. Disconnect 2-pin LPL connector C014. Connect test light between harness connector terminals. Crank engine. If test light illuminates, go to next step. If test light does not illuminate, check relay. See «LOCK-OFF RELAY»(ref-9314-S38627876982000102600000) .
16. Connect switch box from CNG Tank Venting Kit (J-42435) to LPL and vehicle battery. Using switch box, turn LPL on and off. If LPL operates, go to next step. If LPL does not operate, go to step 21 .
17. Check for kinks, bends, damage and obstruction in fuel line between LPL and HPR. If no problem is found, go to next step. If any problem is found, repair as necessary. After repairs, go to step 22 .
18. Replace low pressure regulator. After repairs, go to step 22 .
19. If sent from step 9 , check for kinks, bends, damage and obstruction in fuel line between HPL and HPR. Repair as necessary. If no problem is found or sent from any other step, replace high pressure regulator. After repairs, go to step 22 .
20. Replace high pressure lock-off solenoid. After repairs, go to step 22 .
21. Replace low pressure lock-off solenoid. After repairs, go to next step.
22. Relieve fuel system pressure. See BASIC FUEL SYSTEM CHECKS (CNG) in appropriate BASIC DIAGNOSTIC PROCEDURES article. Turn ignition off. Remove all test equipment. Ensure PRD and test port plugs are installed using Teflon® sealant, not tape. Star engine. Check for system leaks. Repair any leaks as necessary. Using scan tool, clear DTCs from AF ECU and VCM. Turn ignition off for 30 seconds. Start engine. Test drive vehicle. If driveability is okay and MIL does not illuminate, test is complete. If driveability problems exist and/or MIL illuminates, check system. See ON BOARD DIAGNOSTIC (OBD) SYSTEM CHECK under SELF-DIAGNOSTIC SYSTEM in appropriate SELF-DIAGNOSTICS article.

CNG vehicles have 2 modes, gasoline and natural gas operation (NGO). Vehicle operates on CNG except during the following conditions

1. Fuel pressure sensor indicates CNG tank is empty.
2. A wide-open Mixture Control Valve (MCV) is detected.
3. AF ECU detects a system fault. Not all DTCs will cause gasoline operation.
4. Engine crank time exceeds 8 seconds.
5. Every 100 starts, vehicle will start and run briefly on gasoline.
6. When engine coolant temperature is less than 10°F (-12°C), vehicle will start and run briefly on gasoline.
7. If CNG fuse (20-amp) is removed from underhood fuse block.

Switch to CNG will only take place during deceleration. Under certain heavy load conditions, switch to gasoline may occur. Perform system diagnosis to verify system pressure is sufficient. See FUEL SYSTEM DIAGNOSIS (ALTERNATIVE FUEL) . Fuel Indicator Light (FIL), located on fuel gauge select switch will illuminate during gasoline operation.

1. Perform OBD system check. See ON BOARD DIAGNOSTIC (OBD) SYSTEM CHECK under SELF-DIAGNOSTIC SYSTEM in appropriate SELF-DIAGNOSTICS article. Go to next step.
2. Using scan tool, monitor AF ECU NGO enable input and output data parameters. Start engine. If NGO is enabled, go to next step. If NGO is not enabled, go to step 5 .
3. Check Fuel Indicator Light (FIL), located on fuel gauge select switch. If FIL is not illuminated, go to next step. If FIL is illuminated (gasoline operation), see «FUEL GAUGE SELECTOR SWITCH/FUEL INDICATOR LIGHT»(ref-9314-S30531723182000102600000) .
4. Fault is not present at this time. If problem still exists, perform OBD system check. See ON BOARD DIAGNOSTIC (OBD) SYSTEM CHECK under SELF-DIAGNOSTIC SYSTEM in appropriate SELF-DIAGNOSTICS article.
5. Using scan tool, check fuel pressure sensor data. If pressure is 1200 psi or more, go to next step. If pressure is less than 1200 psi, go to step 10 .
6. Using scan tool, command NGO. Check NGO enabled data. If NGO is enabled, go to next step. If NGO is not enabled, go to step 13 .
7. Check fuel pressure sensor, engine coolant sensor and mixture control valve. If no problem is found, go to next step. If any problem is found, repair as necessary. After repairs, go to step 21 .
8. Check ignition sensors (CMP and CKP). Check secondary ignition system. Check all control module grounds. If no problem is found, go to next step. If any problem is found, repair as necessary. After repairs, go to step 21 .
9. Perform «FUEL SYSTEM DIAGNOSIS (ALTERNATIVE FUEL)»(ref-9314-S33519839542000102400000) , then return to this step. If no repairs were required, go to step 20 . If any repairs were required, go to step 21 .
10. Start engine. Using scan tool, command HPL open. If FPS data is less than 1200 psi, go to next step. If FPS data is 1200 psi or more, go to step 15 .
11. Ensure CNG tank is full by connecting vehicle to refilling station and filling tank. Turn ignition on. Compare filling station pressure reading to scan tool Fuel Pressure Sensor (FPS) data reading. If FPS is accurate, go to next step. If FPS is not accurate, see «CNG FUEL GAUGE READING INACCURATE»(ref-9314-S36359362002000102600000) .
12. Monitor FPS data. Start engine. Ensure vehicle is operating on CNG. Allow engine to idle for a few minutes. If FPS is ever less than 1200 psi, go to step 20 . If FPS remains at 1200 psi or more, go to step 21 .
13. Using scan tool, monitor VCM NGO data. Turn ignition off. Disconnect AF ECU connectors. Using a fused jumper wire, connect AF ECU harness connector C001 terminal No. 3 (Pink wire) to ground. Turn ignition on. Check NGO enabled data. If NGO is not enabled, go to next step. If NGO is enabled, go to step 16 .
14. Check for open circuit on Pink wire between AF ECU harness connector C001 terminal No. 3 and VCM harness connector C4 terminal No. 2. Check for poor contact at terminals. Check VCM calibration. If no problem is found, go to step 17 . If any problem is found, repair as necessary. After repairs, go to step 21 .
15. Check CNG system for leaks. Check low pressure lock off solenoid for pressure hold after shut-off. Check high pressure lock off solenoid for pulse prime at start-up. Repair as necessary. After repairs, go to step 21 .
16. Check contact at AF ECU and harness connector C001 terminal No. 3 (Pink wire). If no problem is found, go to step 18 . If any problem is found, repair as necessary. After repairs, go to step 21 .
17. Replace VCM. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. Program VCM while operating vehicle on gasoline. To ensure vehicle is operating on gasoline, remove CNG fuse (20-amp) from underhood fuse block. After repairs, go to step 21 .
18. Replace AF ECU. After repairs, go to step 21 .
19. Replace high pressure lock off solenoid. After repairs, go to step 21 .
20. Replace Gas Mass Sensor/Mixture Control Valve (GMS/MCV). After repairs, go to next step.
21. Reconnect all components and connectors. Using scan tool, clear all DTCs. Turn ignition off for 30 seconds. Start engine. Test drive vehicle. If no problems are found, MIL operates properly and no DTCs are set, test is complete. If any problems are found, MIL does not operate properly or DTCs are set, perform OBD system check. See ON BOARD DIAGNOSTIC (OBD) SYSTEM CHECK under SELF-DIAGNOSTIC SYSTEM in appropriate SELF-DIAGNOSTICS article.

IDLE AIR CONTROL SYSTEM DIAGNOSIS

1. Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. Go to next step.
2. Set parking brake and block wheels. Turn A/C off. Start engine and let idle. Install scan tool and select SPECIAL FUNCTIONS. Select IAC SYSTEM TEST, and then RPM CONTROL. Using scan tool, command engine speed to 500 RPM. If actual engine RPM is within 100 RPM of scan tool display, go to next step. If actual engine RPM is not within 100 RPM of scan tool display, go to step 4.
3. Using scan tool, command engine speed to 1200 RPM. If actual engine RPM is within 100 RPM of scan tool display, check for a non-IAC system problem (i.e., vacuum leak, sticking throttle cable, fuel system lean or rich, throttle body, poor electrical connections, faulty PCV valve, A/C compressor circuits). If actual engine RPM is not within 100 RPM of scan tool display, go to step 5.
4. Check for vacuum leaks, sticking throttle plates, faulty PCV valve, or restriction in air induction system. If problem exists, go to step 20. If problem does not exist, go to step 6.
5. Check for obstruction or excessive carbon deposit in throttle body IAC passages. If problem exists, go to step 21. If problem does not exist, go to next step.
6. Turn ignition off. Disconnect IAC valve harness connector. Check for poor connection at IAC valve. If problem exists, go to step 19. If problem does not exist, go to next step.
7. Connect IAC Driver (J-37027-A) to IAC valve. Set parking brake and block wheels. Turn A/C off. Start engine and let idle. Install scan tool and monitor engine RPM. Using IAC driver, extend and retract IAC valve. If engine RPM decreases and increases as IAC valve is cycled, go to next step. If engine RPM does not decrease and increase as IAC valve is cycled, go to step 22.
8. If RPM changes smoothly with each flash of IAC valve cycle, go to next step. If RPM does not change smoothly with each flash of IAC valve cycle, go to step 22.
9. Install appropriate IAC node light onto IAC valve harness connector. Cycle IAC driver and observe lights. Both lights should cycle Green to Red, but never off as RPM changed over its range. If lights flash as specified, go to next step. If lights do not flash as specified, go to step 12.
10. Remove IAC driver from IAC valve. Using DVOM, measure resistance between IAC valve terminals "A" and "B". (Scheme 8) Also, measure resistance between IAC valve terminals "C" and "D". If resistance is 40-80 ohms on both measurements, go to next step. If resistance is not 40-80 ohms on both measurements, go to step 22.
11. Using DVOM, measure resistance between IAC valve terminals "B" and "C". (Scheme 8) Also, measure resistance between IAC valve terminals "A" and "D". If resistance is infinite on both measurements, check for a non-IAC system problem (i.e., vacuum leak, sticking throttle cable, fuel system lean or rich, throttle body, poor electrical connections, faulty PCV valve, A/C compressor circuits). If resistance is not infinite on both measurements, go to step 22.
12. Turn ignition off. Disconnect PCM harness connectors. Check for poor connections at PCM. If problem exists, go to step 19. If problem does not exist, go to next step.
13. Remove IAC node light. Check for an open in IAC driver circuits between IAC valve harness connector and PCM harness connector. If problem exists, go to step 19. If problem does not exist, go to next step.
14. Using a test light connected to battery voltage, probe IAC valve harness connector terminals. If test light illuminates at any terminal, go to step 17. If test light does not illuminate at any terminal, go to next step.
15. Turn ignition on with engine off. Using a test light connected to ground, probe IAC valve harness connector terminals. If test light illuminates at any terminal, go to step 18. If test light does not illuminate at any terminal, go to next step.
16. Check for a short between IAC valve circuits. If problem exists, go to step 19. If problem does not exist, go to step 23.
17. Repair short to ground in IAC circuit. After repairs, go to step 24.
18. Repair short to voltage in IAC circuit. After repairs, go to step 24.
19. Repair circuit as necessary. After repairs, go to step 24.
20. Repair condition as necessary. After repairs, go to step 24.
21. Clean IAC passages. After repairs, go to step 24.
22. Replace IAC valve. After repairs, go to step 24.
23. Replace PCM. Program PCM. Perform VTD password relearn procedure and crankshaft variation learn procedure. See COMPUTER RELEARN PROCEDURES article in GENERAL INFORMATION. After repairs, go to next step.
24. Install scan tool. Start engine and let idle. Turn off all accessories. Using scan tool, command engine speed to 1200 RPM, and then down to 500 RPM. Again, using scan tool, command engine speed as specified. If actual RPM is close to commanded RPM, system is okay. If actual RPM is not close to commanded RPM, go to step 2.

Scheme 8

Secondary Air Injection System Diagnosis (5.0L & 5.7L "C" & "K" Series)

Note. For circuit and connector terminal identification, see WIRING DIAGRAMS article.

1. Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. Go to next step.
2. Install scan tool. Start engine and let idle until normal operating temperature is obtained. Using scan tool, verify engine is at normal operating temperature and operating in closed loop. Using scan tool, command air pump on. If short term fuel trim indicates 16 percent within 30 seconds, go to next step. If short term fuel trim does not indicate 16 percent within 30 seconds, go to step 4 .
3. If any DTCs exist, perform appropriate DTC test. See appropriate SELF-DIAGNOSTICS article. If no DTCs exist, check the following and repair as necessary: Loose air pump belt. Poor connection at PCM or any secondary air injection system component. Damaged wiring harness. Pinched, kinked or restricted air pipes, line or fittings.
4. Turn ignition on with engine off. Using scan tool, command air pump on. If air pump runs, go to next step. If air pump does not run, go to step 9 .
5. Using scan tool, command air pump off. If air pump continues to run, go to next step. If air pump turns off, go to step 20 .
6. Turn ignition off. Remove air pump relay. Turn ignition on with engine off. If air pump continues to run, go to step 35 . If air pump turns off, go to next step.
7. Using a test light connected to battery voltage, probe air pump relay control circuit (Brown wire) at air pump relay connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 43 .
8. Turn ignition off. Disconnect VCM harness connectors. Turn ignition on with engine off. Using a test light connected to battery voltage, probe air pump relay control circuit (Brown wire) at air pump relay connector. If test light illuminates, go to step 41 . If test light does not illuminate, go to step 47 .
9. Turn ignition off. Disconnect air pump connector. Check for poor connection at air pump. If problem exists, go to step 33 . If problem does not exist, go to next step.
10. Turn ignition on with engine off. Using a test light connected to ground, probe air pump feed circuit (Red wire) at air pump connector (engine side). Using scan tool, command air pump on. If test light illuminates, go to next step. If test light does not illuminate, go to step 12 .
11. Using a test light connected to ground, probe air pump ground circuit (Black wire) at air pump connector (engine side). If test light illuminates, go to step 46 . If test light does not illuminate, go to step 34 .
12. Turn ignition off. Disconnect air pump relay connector. Check for poor connection at air pump relay. If problem exists, go to step 33 . If problem does not exist, go to next step.
13. Check for open in air pump feed circuit (Red wire) between air pump relay and air pump. If problem does not exist, go to next step. If problem exist, go to step 33 .
14. Using a test light connected to ground, probe battery feed circuit (Red wire) at air pump relay connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 36 .
15. Turn ignition on. Using a test light connected to ground, probe ignition feed circuit (Pink wire) at air pump relay connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 37 .
16. Using a test light connected to battery voltage, probe air pump relay control circuit (Brown wire) at air pump relay connector. Using scan tool, command air pump on. If test light illuminates, go to step 43 . If test light does not illuminate, go to next step.
17. Turn ignition off. Disconnect VCM harness connectors. Check for poor connections at VCM. If problem does not exist, go to next step. If problem exist, go to step 33 .
18. Check for open in air pump relay control circuit (Brown wire) between air pump relay and VCM. If problem does not exist, go to next step. If problem exist, go to step 33 .
19. Turn ignition on. Using a test light connected to ground, probe air pump relay control circuit (Brown wire) at air pump relay connector. If test light illuminates, go to step 38 . If test light does not illuminate, go to step 47 .
20. Disconnect air pump output hose at air shutoff valve. Start engine and let idle. Using scan tool, command air pump on. If air flows from air shutoff valve, go to next step. If air does not flow from air shutoff valve, go to step 23 .
21. Disconnect vacuum hose from air shutoff valve. Install a vacuum gauge on air shutoff valve vacuum hose. Using scan tool, command air pump off. If vacuum is present at vacuum hose, go to step 45 . If vacuum is not present at vacuum hose, go to next step.
22. Turn ignition off. Turn ignition on with engine off. Using scan tool, command air pump on. If air flows from air shutoff valve, go to step 44 . If air does not flow from air shutoff valve, go to step 30 .
23. Turn ignition off. Disconnect air pump output hose from air shutoff valve. Turn ignition on with engine off. Using scan tool, command air pump on. If air flows from output hose, go to next step. If air does not flow from output hose, go to step 31 .
24. Disconnect vacuum hose from air shutoff valve. Install a vacuum gauge on air shutoff valve vacuum hose. Start engine and let idle. Using scan tool, command air pump on. If vacuum is greater than 10 in. Hg while air pump is running, go to step 44 . If vacuum is less than 10 in. Hg while air pump is running, go to next step.
25. Check for leak or restriction in vacuum hose between air solenoid and air shutoff valve. If problem exists, go to step 42 . If problem does not exist, go to next step.
26. Remove vacuum connector from air solenoid. Install a vacuum gauge on source hose coming from engine. Measure vacuum with engine running. If vacuum is greater than 10 in. Hg, go to next step. If vacuum is less than 10 in. Hg, go to step 32 .
27. Turn ignition off. Disconnect air solenoid connector. Check for poor connection at air solenoid. If problem exists, go to step 33 . If problem does not exist, go to next step.
28. Turn ignition on with engine off. Using a test light connected to ground, probe air solenoid feed circuit (Red wire) at air solenoid connector. Using scan tool, command air pump on. If test light illuminates, go to next step. If test light does not illuminate, go to step 40 .
29. Turn ignition off. Using a test light connected to battery voltage, probe air solenoid ground circuit (Black wire) at air solenoid connector. If test light illuminates, go to step 45 . If test light does not illuminate, go to step 39 .
30. Check for leaks or restrictions in air shutoff valve, hoses, check valves, fittings, air pipes, and/or exhaust manifolds. If problem exists, go to step 42 . If problem does not exist, check the following and repair as necessary: Loose air pump belt. Poor connection at PCM or any secondary air injection system component. Damaged wiring harness. Pinched, kinked or restricted air pipes, line or fittings.
31. Check for restriction or obstruction in air pump inlet hose. If problem exists, go to step 42 . If problem does not exist, go to step 46 .
32. Repair leak or restriction in air solenoid vacuum supply hose. After repairs, go to step 48 .
33. Repair circuit as necessary. After repairs, go to step 48 .
34. Repair open in air pump ground circuit. After repairs, go to step 48 .
35. Repair short to voltage in air pump feed circuit. After repairs, go to step 48 .
36. Repair open or short to ground in air pump relay battery feed circuit. After repairs, go to step 48 .
37. Repair open or short to ground in air pump relay ignition feed circuit. After repairs, go to step 48 .
38. Repair short to voltage in air pump relay control circuit. After repairs, go to step 48 .
39. Repair open in air solenoid ground circuit. After repairs, go to step 48 .
40. Repair open in air solenoid feed circuit. After repairs, go to step 48 .
41. Repair short to ground in air pump relay control circuit. After repairs, go to step 48 .
42. Repair as necessary. After repairs, go to step 48 .
43. Replace air pump relay. After repairs, go to step 48 .
44. Replace air shutoff valve. After repairs, go to step 48 .
45. Replace air solenoid. After repairs, go to step 48 .
46. Replace air pump. After repairs, go to step 48 .
47. Replace VCM. Program VCM. Perform VTD password relearn procedure and crankshaft variation learn procedure. See COMPUTER RELEARN PROCEDURES article in GENERAL INFORMATION. After repairs, go to next step.
48. Install scan tool. Start engine and let idle until normal operating temperature is obtained. Using scan tool, verify engine is at normal operating temperature and operating in closed loop. Using scan tool, command air pump on. If short term fuel trim indicates 16 percent within 30 seconds, system is okay. If short term fuel trim does not indicate 16 percent within 30 seconds, go to step 4 .

Secondary Air Injection System Diagnosis (7.4L)

Note. For circuit and connector terminal identification, see WIRING DIAGRAMS article.

1. Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. Go to next step.
2. Install scan tool. Start engine and let idle until normal operating temperature is obtained. Using scan tool, verify engine is at normal operating temperature and operating in closed loop. Using scan tool, command air pump on. If short term fuel trim indicates 16 percent within 30 seconds, go to next step. If short term fuel trim does not indicate 16 percent within 30 seconds, go to step 4 .
3. If any DTCs exist, perform appropriate DTC test. See appropriate SELF-DIAGNOSTICS article. If no DTCs exist, check the following and repair as necessary: Loose air pump belt. Poor connection at PCM or any secondary air injection system component. Damaged wiring harness. Pinched, kinked or restricted air pipes, line or fittings.
4. Ensure engine is still running. Using scan tool, command air pump on. If air pump clutch is engaged, go to next step. If air pump clutch is not engaged, go to step 9 .
5. Ensure engine is still running. Using scan tool, command air pump off. If air pump clutch is engaged, go to next step. If air pump clutch is not engaged, go to step 19 .
6. Turn ignition off. Remove air pump relay. Turn ignition switch on. Using a test light connected to battery voltage, probe air pump relay control circuit (Brown wire) at air pump relay connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 8 .
7. Turn ignition off. Disconnect VCM harness connectors. Using a test light connected to battery voltage, probe air pump relay control circuit (Brown wire) at air pump relay connector. If test light illuminates, go to step 30 . If test light does not illuminate, go to step 36 .
8. Turn ignition on. Using a test light connected to ground, probe air pump feed circuit (Red wire) at air pump relay connector. If test light illuminates, go to step 31 . If test light does not illuminate, go to step 33 .
9. Turn ignition off. Disconnect air pump clutch connector. Check for poor connection at air pump clutch. If problem exists, go to step 26 . If problem does not exist, go to next step.
10. Turn ignition on with engine off. Using a test light connected to ground, probe air pump clutch feed circuit (Red wire) at air pump clutch connector. Using scan tool, command air pump on. If test light illuminates, go to next step. If test light does not illuminate, go to step 12 .
11. Using a test light connected to ground, probe air pump clutch ground circuit (Black wire) at air pump clutch connector. If test light illuminates, go to step 35 . If test light does not illuminate, go to step 27 .
12. Turn ignition off. Disconnect air pump relay connector. Check for poor connection at air pump relay. If problem exists, go to step 26 . If problem does not exist, go to next step.
13. Check for open in air pump clutch feed circuit. If problem exists, go to step 26 . If problem does not exist, go to next step.
14. Turn ignition on. Using a test light connected to ground, probe both ignition feed circuits (Pink wires) at air pump relay socket. If test light illuminates on both terminals, go to next step. If test light does not illuminate on both terminals, go to step 28 .
15. Using a test light connected to battery voltage, probe air pump relay control circuit (Brown wire) at air pump relay connector. Using scan tool, command air pump on. If test light illuminates, go to step 33 . If test light does not illuminate, go to next step.
16. Turn ignition off. Disconnect VCM harness connector. Check for poor connection at VCM. If problem exists, go to step 26 . If problem does not exist, go to next step.
17. Check for open in air pump relay control circuit. If problem exists, go to step 26 . If problem does not exist, go to next step.
18. Turn ignition on. Using a test light connected to ground, probe air pump relay control circuit (Brown wire) at VCM harness connector. If test light illuminates, go to step 29 . If test light does not illuminate, go to step 36 .
19. Turn ignition off. Disconnect air output hose at output of air shutoff valve. Start engine and let idle. Using scan tool, command air pump on. If air flows from air shutoff valve, go to step 24 . If air does not flow from air shutoff valve, go to next step.
20. Turn ignition off. Disconnect air output hose at inlet of air shutoff valve. Start engine and let idle. Using scan tool, command air pump on. If air flows from output hose, go to next step. If air does not flow from output hose, go to step 23 .
21. Using scan tool, command air pump on. Accelerate engine to about 1500 RPM. If airflow increases as engine is accelerated, go to next step. If airflow does not increase as engine is accelerated, go to step 25 .
22. Check for leaks or loose connections in hose between air pump and air shutoff valve. If problem exists, go to step 32 . If problem does not exist, go to step 34 .
23. Check for leaks or obstructions in hose between air pump and air shutoff valve. If problem exists, go to step 32 . If problem does not exist, go to step 25 .
24. Check for leaks or restrictions in air shutoff valve, hoses, check valves, fittings, air pipes, and/or exhaust manifolds. If problem exists, go to step 32 . If problem does not exist, check the following and repair as necessary: Loose air pump belt. Poor connection at PCM or any secondary air injection system component. Damaged wiring harness. Pinched, kinked or restricted air pipes, line or fittings.
25. Check for restriction or obstruction in air pump inlet hose. If problem exists, go to step 32 . If problem does not exist, go to step 35 .
26. Repair circuit as necessary. After repairs, go to step 37 .
27. Repair open in air pump clutch ground circuit. After repairs, go to step 37 .
28. Repair open or short to ground in ignition feed circuits. After repairs, go to step 37 .
29. Repair short to voltage in air pump relay control circuit. After repairs, go to step 37 .
30. Repair short to ground in air pump relay control circuit. After repairs, go to step 37 .
31. Repair short to voltage in air pump clutch feed circuit. After repairs, go to step 37 .
32. Repair as necessary. After repairs, go to step 37 .
33. Replace air pump relay. After repairs, go to step 37 .
34. Replace air shutoff valve. After repairs, go to step 37 .
35. Replace air pump. After repairs, go to step 37 .
36. Replace VCM. Program VCM. Perform VTD password relearn procedure and crankshaft variation learn procedure. See COMPUTER RELEARN PROCEDURES article in GENERAL INFORMATION. After repairs, go to next step.
37. Install scan tool. Start engine and let idle until normal operating temperature is obtained. Using scan tool, verify engine is at normal operating temperature and operating in closed loop. Using scan tool, command air pump on. If short term fuel trim indicates 16 percent within 30 seconds, system is okay. If short term fuel trim does not indicate 16 percent within 30 seconds, go to step 4 .

EGR System Diagnosis

1. Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. Go to next step.
2. Set parking brake and block wheels. Install scan tool. Start engine and let idle until normal operating temperature is obtained. Using scan tool, check actual EGR position. If scan tool indicates greater than zero percent, go to step 4. If scan tool indicates zero percent, go to next step.
3. Turn ignition on with engine off. Using scan tool, command EGR position to 100 percent. If actual EGR position follows the commanded EGR position, go to step 17. If the actual EGR position does not follow commanded EGR position, go to step 6.
4. Disconnect EGR valve harness connector. If scan tool indicates greater than zero percent, go to step 16. If scan tool indicates zero percent, go to next step.
5. Turn ignition off. Connect a test light between EGR valve feed circuit (Red wire) and EGR valve control circuit (White wire) at EGR valve harness connector. (Scheme 9) Turn ignition on with engine off. If test light illuminates, go to step 15. If test light does not illuminate, go to step 10.
6. Turn ignition on with engine off. Connect a test light between EGR valve feed circuit (Red wire) and EGR valve control circuit (White wire) at EGR valve harness connector. (Scheme 9) Using scan tool, command EGR position to 100 percent. If test light illuminates, go to step 13. If test light does not illuminate, go to next step.
7. Turn ignition off. Using a test light connected to battery voltage, probe EGR valve control circuit (White wire) at EGR valve harness connector. (Scheme 9) If test light illuminates, go to next step. If test light does not illuminate, go to step 9.
8. Check for an open in EGR valve feed circuit. If problem exists, go to step 22. If problem does not exist, go to step 21.
9. Check for open, high resistance or short to voltage in EGR valve control circuit. If problem exists, go to step 22. If problem does not exist, go to step 21.
10. Turn ignition on with engine off. Using a DVOM connected to ground, probe EGR reference voltage circuit (Gray wire) at EGR valve harness connector. (Scheme 9) If voltage is greater than 5.2 volts, go to step 22. If voltage is 5.2 volts or less, go to next step.
11. Turn ignition off. Using a test light connected to battery voltage, probe EGR sensor ground circuit (Black wire) at EGR valve harness connector. (Scheme 9) If test light illuminates, go to step 19. If test light does not illuminate, go to next step.
12. Turn ignition off. Disconnect VCM harness connectors. Check for open in EGR sensor ground circuit. If problem exists, go to step 22. If problem does not exist, go to step 21.
13. Turn ignition on with engine off. Using a DVOM connected to ground, probe EGR reference voltage circuit (Gray wire) at EGR valve harness connector. (Scheme 9) If voltage is near 5.2 volts, go to next step. If voltage is not near 5.2 volts, go to step 22.
14. Disconnect EGR valve harness connector. Install jumper wire between EGR reference voltage circuit (Gray wire) and EGR pintle position signal circuit (Brown wire) at EGR valve harness connector. (Scheme 9) Turn ignition on with engine off. If actual EGR position is near 100 percent, go to step 19. If actual EGR position is not near 100 percent, go to step 20.
15. Disconnect VCM harness connector. Turn ignition on with engine off. Check for short to voltage in EGR valve feed circuit. If problem exists, go to step 22. If problem does not exist, go to step 23.
16. Disconnect VCM harness connectors. Turn ignition on with engine off. Check for short to voltage in EGR pintle position signal circuit. If problem exists, go to step 22. If problem does not exist, go to step 23.
17. Start engine. Observe MAP sensor reading. Using scan tool, command EGR position to 30 percent. Observe MAP sensor reading again. If MAP sensor reading increases, go to step 24. If MAP sensor reading does not increase, go to next step.
18. Repair blockage in EGR valve passages. After repairs, go to step 24.
19. Replace EGR valve. After repairs, go to step 24.
20. Check for short to ground in EGR pintle position signal circuit. If problem exists, go to step 22. If problem does not exist, go to next step.
21. Check for poor connections at VCM. If problem exists, go to step 22. If problem does not exist, go to step 23.
22. Repair circuit as necessary. After repairs, go to step 24.
23. Replace VCM and reprogram. Perform VTD password relearn procedure and crankshaft variation learn procedure. See COMPUTER RELEARN PROCEDURES article in GENERAL INFORMATION. After repairs, go to next step.
24. Set parking brake and block wheels. Install scan tool. Start engine and let idle until normal operating temperature is obtained. Using scan tool, command EGR on and off. If actual EGR position follows the commanded EGR position, system is okay. If the actual EGR position does not follow commanded EGR position, go to step 2.

Scheme 9

EVAP Control System Diagnosis (2.2L - VIN 4)

1. Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. Go to next step.
2. Install scan tool. Turn ignition on with engine off. Retrieve DTCs. If no DTCs are set, go to next step. If any DTCs are set, perform appropriate DTC test. See appropriate SELF-DIAGNOSTICS article.
3. Using scan tool, command EVAP purge solenoid valve and EVAP canister vent solenoid valve on and off. If both purge solenoid valve and canister vent solenoid valve click when toggled on and off, go to next step. If either purge solenoid valve or vent solenoid valve do not click when toggled on and off, perform PCM output diagnosis. See «PCM OUTPUT DIAGNOSIS (2.2L - VIN 4)»(ref-9314-S03180062782000101700000) under COMPUTERIZED ENGINE CONTROLS.
4. Remove fuel cap. Using scan tool, observe fuel tank pressure. If scan tool displays -1.28-1.28 in. H 2 O, go to next step. If scan tool does not display -1.28 to 1.28 H 2 O, perform DTC P0452 or DTC P0453 test. See appropriate SELF-DIAGNOSTICS article.
5. Reinstall fuel cap. Install EVAP Pressure/Purge Diagnostic Station (J-41413) to EVAP service port and zero gauges. Using scan tool, command EVAP canister vent solenoid valve on. Using diagnostic station, pressurize EVAP system to 5 in. H 2 O. Using scan tool, observe fuel tank pressure. If scan tool displays 3.85-8.99 in. H 2 O, go to next step. If scan tool does not display 3.85-8.99 in. H 2 O, perform DTC P0452 or DTC P0453 test. See appropriate SELF-DIAGNOSTICS article.
6. Observe EVAP system pressure on diagnostic station. Using scan tool, command EVAP canister vent solenoid valve off. If EVAP system pressure decreases to zero in. H 2 O within 5 seconds, go to next step. If EVAP system pressure does not decrease to zero in. H 2 O within 5 seconds, perform DTC P0446 test. See appropriate SELF-DIAGNOSTICS article.
7. Start engine. Remove fuel cap. Using scan tool, select EVAP PURGE/SEAL and seal EVAP system. Using diagnostic station, attempt to pressurize EVAP system to 5 in. H 2 O. If fuel tank pressure does not decrease, go to next step. If fuel tank pressure is decreasing, perform DTC P1441 test. See appropriate SELF-DIAGNOSTICS article.
8. Using scan tool, command EVAP canister vent solenoid valve and EVAP purge solenoid valve on. Increase engine speed to 1500 RPM. Using scan tool, observe fuel tank pressure. If fuel tank pressure is decreasing, system is okay. If fuel tank pressure does not decrease, perform DTC P0440 test. See appropriate SELF-DIAGNOSTICS article.

EVAP Control System Diagnosis (3.4L)

1. Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. Go to next step.
2. Ensure vacuum and purge lines are connected. Check for loose or missing fuel filler cap. Install scan tool. Turn ignition on with engine off. Retrieve DTCs. If no DTCs are set, go to next step. If any DTCs are set, perform appropriate DTC test. See appropriate SELF-DIAGNOSTICS article.
3. Turn ignition off. Remove fuel filler cap to relieve fuel pressure. Turn ignition on with engine off. Using scan tool, observe fuel tank pressure. If fuel tank pressure is zero in. H 2 O, go to next step. If fuel tank pressure is not zero in. H 2 O, perform DTC P0453 test. See appropriate SELF-DIAGNOSTICS article.
4. Turn ignition off. Reinstall fuel cap. Install EVAP Pressure/Purge Diagnostic Station (J-41413) to EVAP service port and zero gauges. Turn ignition on with engine off. Using scan tool, capture and save freeze frame record for DTC 0440. Clear DTCs. Using scan tool, select EVAP PURGE/SEAL and seal EVAP system. Attempt to pressurize EVAP system to 5 in. H 2 O by slowly turning diagnostic station rotary switch to PRESSURE position. Monitor pressure with switch in OFF/HOLD position. If fuel tank pressure is 5 in. H 2 O, go to next step. If fuel tank pressure is not 5 in. H 2 O, perform DTC P0440 test. See appropriate SELF-DIAGNOSTICS article.
5. Maintain fuel tank pressure at 5 in. H 2 O. Monitor pressure with switch in OFF/HOLD position. Using scan tool, observe fuel tank pressure. If fuel tank pressure is 5 in. H 2 O, go to next step. If fuel tank pressure is not 5 in. H 2 O, go to step 10 .
6. Command EVAP canister vent solenoid valve off to relieve pressure through vent solenoid valve. If EVAP pressure gauge decreases to about -5 in. H 2 O within 2 minutes with rotary switch in OFF/HOLD position, go to next step. If EVAP pressure gauge does not decrease to about -5 in. H 2 O within 2 minutes with rotary switch in OFF/HOLD position, perform DTC P0446 test. See appropriate SELF-DIAGNOSTICS article.
7. Connect the in. Hg vacuum gauge of diagnostic station to EVAP purge solenoid valve (canister side). Turn ignition on with engine off. Using scan tool, select EVAP PURGE/SEAL and seal EVAP system. Start engine and let idle. Run engine from 1200-1500 RPM and observe vacuum level. If vacuum is near zero in. Hg, go to next step. If vacuum is not near zero in. Hg, go to step 11 .
8. Using scan tool, increase purge to 100 percent. Run engine from 1200-1500 RPM and observe vacuum level. If vacuum level is greater than 15 in. Hg, go to next step. If vacuum level is 15 in. Hg or less, go to step 12 .
9. Check for kinked or restricted canister purge line between EVAP purge solenoid valve and EVAP canister. Repair as necessary. After repairs, go to step 13 .
10. Check for restricted fuel tank vapor line or EVAP purge line. If problem exists, repair as necessary and go to step 13 . If problem does not exist, perform DTC P0452 test. See appropriate SELF-DIAGNOSTICS article.
11. Check EVAP purge solenoid valve and purge line for carbon contamination. Replace EVAP purge solenoid valve. After repairs, go to step 13 .
12. Check for no source vacuum to EVAP purge solenoid valve. If problem exists, repair as necessary and go to step 2 . If problem does not exist, go to next step.
13. Reconnect all previously disconnect EVAP system components and hardware. Turn ignition on with engine off. Using scan tool, select EVAP PURGE/SEAL and seal EVAP system. Pressurize EVAP system to 15 in. H 2 O by slowly turning diagnostic station rotary switch to PRESSURE position. Monitor pressure with switch in OFF/HOLD position. If EVAP pressure gauge decreases to less than 10 in. H 2 O within 2 minutes with rotary switch in OFF/HOLD position, perform DTC P0442 test. See appropriate SELF-DIAGNOSTICS article. If EVAP pressure gauge does not decrease to less than 10 in. H 2 O within 2 minutes with rotary switch in OFF/HOLD position, system is okay.

EVAP Control System Diagnosis (Except 2.2L & 3.4L)

1. Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. Go to next step.
2. Retrieve DTCs. If DTC P0440, P0442, P0446, P0452, P0453, P0461, P0462, P0463 or P1441 is not set, go to next step. If DTC P0440, P0442, P0446, P0452, P0453, P0461, P0462, P0463 or P1441 is set, perform appropriate DTC test. See appropriate SELF-DIAGNOSTICS article.
3. Inspect EVAP system for the following: Loose, incorrect, defective or missing fuel filler cap. Improperly routed, kinked, or damaged EVAP system purge lines. Damaged EVAP system components. Loose, missing or damaged service port dust cap and/or Schrader valve. If problem exists, repair as necessary and go to step 25 . If problem does not exist, go to next step.
4. Before proceeding with service bay test, ensure DTCs are cleared, battery voltage is 10.5-17.5 volts, fuel level is 15-85 percent, and with ignition on engine temperature is less than 176°F (80°C). Scan tool will display TEST ABORTED when service bay test is activated if the listed criteria are not met. Using scan tool, capture and save freeze frame records. Clear DTCs. Using scan tool, perform service bay test for EVAP system. If vehicle does not pass service bay test, go to next step. If vehicle passes service bay test, inspect EVAP system for the following: Loose, incorrect, defective or missing fuel filler cap. Missing or damaged EVAP canister fuel vapor and purge line fitting "O" rings. Cracked or punctured EVAP canister. Improperly routed, kinked, or damaged EVAP system purge and vapor lines. Disconnected or damaged EVAP purge line, vent hose or fuel tank vapor line. Poor connection at VCM, backed-out terminals, broken locks, improperly formed or damaged terminals, or poor terminal-to-wire connection Damaged EVAP purge solenoid valve, EVAP canister vent solenoid valve of fuel tank pressure sensor wiring harnesses. Kinked, pinched, plugged or restricted EVAP purge or fuel tank vapor line.
5. Turn ignition off. Connect a vacuum gauge directly to purge connection of EVAP purge solenoid valve. Start engine and let idle. Using scan tool, command EVAP purge solenoid valve to 100 percent purge. If vacuum is 12 in. Hg or more, go to next step. If vacuum is less than 12 in. Hg, go to step 11 .
6. Turn ignition off. Disconnect fuel tank vapor line and EVAP purge line from EVAP canister. Plug EVAP canister fuel tank vapor port. Connect a hand-held vacuum pump to EVAP canister purge port. With ignition on, using scan tool, command EVAP vent solenoid valve on. Attempt to apply 5 in. Hg to EVAP canister. If 5 in. Hg can be obtained and held, go to step 9 . If 5 in. Hg cannot be obtained or held, go to next step.
7. Leave system connected as described in step 6 . Disconnect vent line at EVAP canister vent solenoid valve. Plug disconnected vent line. Attempt to apply 5 in. Hg to EVAP canister. If 5 in. Hg can be obtained and held, go to step 15 . If 5 in. Hg cannot be obtained or held, go to next step.
8. Inspect for leaks in EVAP vent line from EVAP canister to EVAP vent solenoid valve. Replace as necessary. If problem exists, go to step 25 . If problem does not exist, go to step 21 .
9. Turn ignition off. Remove plug and hand-held vacuum pump. Reconnect EVAP canister purge and fuel tank vapor lines. Connect EVAP Pressure/Purge Diagnostic Station (J-41413) to EVAP system service port. Using scan tool, command EVAP vent solenoid valve on. Attempt to pressurize EVAP system to 15 in. H 2 O. DO NOT pressurize EVAP system to more than 15 in. H 2 O. Using Ultrasonic Leak Detector (J-41416), locate and repair EVAP system leak. If problem exists, go to step 25 . If problem does not exist, go to next step.
10. Check EVAP system for restrictions. Repair as necessary. If problem exists, go to step 25 . If problem does not exist, go to step 22 .
11. Turn ignition on with engine off. Disconnect EVAP purge solenoid valve connector. Connect a test light between ground and ignition feed circuit of EVAP purge solenoid valve connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 13 .
12. Connect a test light between ignition feed circuit and control circuit of EVAP purge solenoid valve connector. Using scan tool, command EVAP purge solenoid valve on. If test light illuminates, go to step 19 . If test light does not illuminate, go to step 14 .
13. Check for and repair cause of no power to EVAP purge solenoid valve ignition feed circuit. Possible causes may be: Open ignition feed circuit. Shorted ignition feed circuit (open fuse). Shorted EVAP purge solenoid valve (open fuse). No power to EVAP purge solenoid valve fuse (open Maxi-fuse, fuse link, etc.). After repairs, go to step 25 .
14. Check for open in EVAP purge solenoid valve control circuit. Repair as necessary. If problem exists, go to step 25 . If problem does not exist, go to step 24 .
15. Turn ignition on with engine off. Disconnect EVAP canister vent solenoid valve connector. Connect a test light between ground and ignition feed circuit of EVAP canister vent solenoid valve connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 17 .
16. Connect a test light between ignition feed circuit and control circuit of EVAP canister vent solenoid valve connector. Using scan tool, command EVAP canister vent solenoid valve on. If test light illuminates, go to step 20 . If test light does not illuminate, go to step 18 .
17. Check for and repair cause of no power to EVAP canister vent solenoid valve ignition feed circuit. Possible causes may be: Open ignition feed circuit. Shorted ignition feed circuit (open fuse). Shorted EVAP canister vent solenoid valve (open fuse). No power to EVAP canister vent solenoid valve fuse (open Maxi-fuse, fuse link, etc.). After repairs, go to step 25 .
18. Check for open in EVAP canister vent solenoid valve control circuit. Repair as necessary. If problem exists, go to step 25 . If problem does not exist, go to step 24 .
19. Check EVAP purge solenoid valve and purge line for carbon contamination. Replace EVAP purge solenoid valve. After repairs, go to step 25 .
20. Replace EVAP canister vent solenoid valve. After repairs, go to step 25 .
21. Replace EVAP vapor canister. After repairs, go to step 25 .
22. Relieve all system pressure. Using scan tool, select PURGE/SEAL. Turn EVAP purge solenoid valve on to varying vacuum levels with engine running and quickly SEAL system using scan tool. Leaving EVAP purge solenoid valve on for higher percents or longer times will develop a higher level of vacuum. Maximum of 8.5 in. H 2 O of vacuum can be applied to EVAP system using scan tool. While system is sealed, compare EVAP pressure/purge diagnostic station vacuum gauge (H 2 O) to vacuum indicated on scan tool from EVAP fuel tank pressure sensor. Allow system to stabilize for a few seconds. If values indicate the same amount of vacuum in EVAP system within 2 in. H 2 O, go to step 3 . If values do not indicate the same amount of vacuum in EVAP system within 2 in. H 2 O, go to next step.
23. Replace fuel tank pressure sensor. After repairs, go to step 25 .
24. Replace VCM and reprogram. Perform VTD password relearn procedure and crankshaft variation learn procedure. See COMPUTER RELEARN PROCEDURES article in GENERAL INFORMATION. After repairs, go to next step.
25. Using scan tool, clear DTCs. Start engine and let idle until normal operating temperature is obtained. Using scan tool, select DTC, and then SPECIFIC DTC. Enter the DTC number which was set. Operate vehicle under conditions for setting DTC until scan tool indicates the diagnostic ran. If scan tool indicates the diagnostic passed, go to next step. If scan tool does not indicate the diagnostic passed, go to step 2 .
26. If scan tool displays any additional undiagnosed DTCs, perform appropriate DTC test. See appropriate SELF-DIAGNOSTICS article. If scan tool does not display any additional undiagnosed DTCs, system is okay.

Fuel Tank Pressure Sensor Diagnosis (3.4L)

Note. For fuel tank pressure sensor testing not listed, perform related DTC testing procedure. See appropriate SELF-DIAGNOSTICS article.

Note. For component circuit identification, see WIRING DIAGRAMS article.

1. Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. Go to next step.
2. Disconnect fuel tank pressure sensor harness connector. Using DVOM, measure voltage between reference voltage circuit (Gray wire) and sensor ground circuit (Orange/Black wire) at fuel tank pressure sensor harness connector. If voltage is about 5 volts, go to step 5 . If voltage is not about 5 volts, go to next step.
3. Check reference voltage circuit (Gray wire) for poor connection at PCM. If problem exists, go to step 11 . If problem does not exist, go to next step.
4. Check for open or poor connection in reference voltage circuit (Gray wire) to fuel tank pressure sensor harness connector. If problem exists, go to step 12 . If problem does not exist, go to step 8 .
5. Remove fuel cap. Disconnect fuel tank pressure sensor harness connector. Using 2 fused jumper wires, connect reference voltage circuit (Gray wire) and sensor signal circuit (Dark Green wire) between fuel tank pressure sensor and fuel tank pressure sensor harness connector. Using DVOM, measure voltage at sensor signal circuit terminal of fuel tank pressure sensor pigtail. If voltage is 1.3-1.7 volts, go to next step. If voltage is not 1.3-1.7, go to step 13 .
6. Check sensor signal circuit (Dark Green wire) for poor connection at PCM. If problem exists, go to step 11 . If problem does not exist, go to next step.
7. Check for open, short to ground or short to voltage in sensor signal circuit (Dark Green wire) between fuel tank pressure sensor and PCM. If problem exists, go to step 12 . If problem does not exist, go to step 14 .
8. Check sensor ground circuit (Orange/Black wire) for poor terminal connection at PCM. If problem exists, go to step 11 . If problem does not exist, go to next step.
9. Check for open or faulty splice in sensor ground circuit (Orange/Black wire). If problem exists, go to step 12 . If problem does not exist, go to step 14 .
10. Check for poor terminal connection at fuel tank pressure sensor connector. If problem exists, go to next step. If problem does not exist, go to step 13 .
11. Replace faulty harness connector terminals as necessary. After repairs, go to step 15 .
12. Locate and repair open or short circuit in wiring harness as necessary. After repairs, go to step 15 .
13. Replace fuel tank pressure sensor. After repairs, go to step 15 .
14. Replace PCM and reprogram. Perform VTD password relearn procedure and perform crankshaft variation learn procedure. See COMPUTER RELEARN PROCEDURES in GENERAL INFORMATION. After repairs, go to next step.
15. Turn ignition off. Remove fuel cap. Turn ignition on. Using scan tool, observe fuel tank pressure. If fuel tank pressure is zero in. H 2 O, go to next step. If fuel tank pressure is not zero in. H 2 O, go to step 2 .
16. Connect EVAP Pressure/Purge Diagnostic Station (J-41413) to EVAP system service port. Using scan tool, command EVAP vent solenoid valve on. Pressurize EVAP system to 5 in. H 2 O. Using scan tool, observe fuel tank pressure. If problem exists, system is okay. If problem does not exist, go to step 2 .

Generator Circuit Diagnosis (2.2L - VIN 4)

1. Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. Go to next step.
2. Turn ignition on with engine off. If charging system light illuminates, go to next step. If charging system light does not illuminate, go to step 4 .
3. Start engine. If charging system light goes out, go to step 17 . If charging system light remains illuminated, go to step 5 .
4. Turn ignition off. Disconnect generator connector. Turn ignition on with ignition off. If charging system light illuminates, go to step 6 . If charging system light does not illuminate, go to step 7 .
5. Turn all accessories off. Install scan tool. If voltage is greater than 12 volts, go to step 7 . If voltage is 12 volts or less, go to step 8 .
6. With test light connected to ground, probe light driver output circuit at generator connector. See WIRING DIAGRAMS article. If test light illuminates, go to step 9 . If test light does not illuminate, go to step 10 .
7. Replace instrument cluster. After repairs, go to step 17 .
8. Turn ignition off. Disconnect generator connector. Turn ignition on with engine off. Using a test light connected to ground, probe light driver output circuit at generator connector. See WIRING DIAGRAMS article. If test light illuminates, go to step 11 . If test light does not illuminate, go to step 12 .
9. Repair short to voltage in light driver output circuit. After repairs, go to step 17 .
10. Replace generator. After repairs, go to step 17 .
11. Repair short to ground in light driver output circuit. After repairs, go to step 17 .
12. Using DVOM connected to ground, probe light driver output circuit at generator connector. See WIRING DIAGRAMS article. If voltage is greater than 4.5 volts, go to next step. If voltage is 4.5 volts or less, go to step 14 .
13. Using DVOM connected to ground, probe battery circuit at generator connector. See WIRING DIAGRAMS article. If battery voltage exists, go to step 10 . If battery voltage does not exist, go to step 15 .
14. Check for poor connection or open in light driver output circuit. If problem exists, repair as necessary and go to step 17 . If problem does not exist, go to step 16 .
15. Check for poor connection or open in battery circuit. Repair as necessary. After repairs, go to step 17 .
16. Replace PCM and reprogram. Perform VTD password relearn procedure and perform crankshaft variation learn procedure. See COMPUTER RELEARN PROCEDURES in GENERAL INFORMATION article. After repairs, go to next step.
17. Start engine and operate vehicle under condition under which original symptom was noted. If system does not operate properly, go to step 2 . If system operates properly, check for poor connection at PCM, backed-out terminals, broken locks, improperly formed or damaged terminals, or poor terminal-to-wire connection.

Shift Light Circuit Diagnosis (Manual Transmission)

1. Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. Go to next step.
2. Turn ignition off. Install scan tool. Turn ignition on. Using scan tool, command shift light on. If shift light illuminates, go to step 4 . If shift light does not illuminate, go to next step.
3. Turn ignition off. Disconnect PCM harness connector that contains shift light circuit. Turn ignition on. Connect a fused jumper wire between ground and shift light control circuit (Tan/Black wire) at PCM harness connector. If shift light illuminates, go to step 5 . If shift light does not illuminate, go to step 6 .
4. Using scan tool, command shift light off, and then on. If shift light operates as commanded, system is okay. If shift light does not operate as commanded, go to step 8 .
5. Check shift light control circuit (Tan/Black wire) for poor connection at PCM. If problem exists, go to step 7 . If problem does not exist, go to step 10 .
6. Repair open in shift light control circuit between PCM and instrument cluster. After repairs, go to step 11 .
7. Repair poor connection as necessary. After repairs, go to step 11 .
8. Turn ignition off. Disconnect PCM harness connector that contains shift light circuit. Turn ignition on. If shift light illuminates, go to next step. If shift light does not illuminate, go to step 10 .
9. Repair short to ground in shift light control circuit (Tan/Black wire) between PCM and instrument cluster. After repairs, go to step 11 .
10. Replace PCM and reprogram. Perform VTD password relearn procedure and perform crankshaft variation learn procedure. See COMPUTER RELEARN PROCEDURES in GENERAL INFORMATION article. After repairs, go to next step.
11. Using scan tool, clear DTCs. Start engine and let idle until normal operating temperature is obtained. Using scan tool, select DTC, and then SPECIFIC DTC. Enter the DTC number which was set. Operate vehicle under conditions for setting DTC until scan tool indicates the diagnostic ran. If scan tool indicates the diagnostic passed, go to next step. If scan tool does not indicate the diagnostic passed, go to step 2
12. If scan tool does not display any DTCs, system is okay. If scan tool displays any DTCs, perform appropriate DTC test. See appropriate SELF-DIAGNOSTICS article.

Tachometer Control Circuit Diagnosis (4.3L)

Note. Before clearing DTCs, use scan tool to capture and save freeze frame records for reference. Information will be deleted when DTCs are cleared.

1. Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. Go to next step.
2. Install scan tool. Using scan tool, select BODY (IPC) diagnosis tachometer sweep test function. Sweep tachometer needle on and off. If tachometer needle sweeps when commanded, go to next step. If tachometer needle does not sweep when commanded, diagnose instrument cluster. See appropriate INSTRUMENT PANELS article in ACCESSORIES & EQUIPMENT.
3. Using scan tool, select POWERTRAIN tachometer control. Start engine and let idle. Using scan tool, command tachometer output to 600 RPM, and then to 6000 RPM. Compare scan tool display to actual tachometer value displayed on instrument cluster. If scan tool display matches instrument cluster display, system is okay. If scan tool display does not match instrument cluster display, go to next step.
4. Disconnect instrument cluster connector that contains tachometer output circuit. Using scan tool, select POWERTRAIN tachometer control. Connect DVOM between ground and tachometer circuit of instrument cluster connector (harness side) and measure AC frequency (press Hz button) of tachometer circuit. Start engine and let idle. Using scan tool, command tachometer output to 600 RPM, and then to 6000 RPM. Compare DVOM display to specifications in table. See «FREQUENCY VS. RPM»(ref-9314-S29621174222000101700000) table. If DVOM display matches table specifications, diagnose instrument cluster. See appropriate INSTRUMENT PANELS article in ACCESSORIES & EQUIPMENT. If DVOM display does not match table specifications, go to next step.
5. Check for open, short to ground or short to voltage in tachometer output circuit. See WIRING DIAGRAMS article. If problem exists, go to next step. If problem does not exist, go to step 7 .
6. Repair circuit as necessary. After repairs, go to step 3 .
7. Check for poor connection at VCM. If problem exists, repair as necessary and go to step 3 . If problem does not exist, go to next step.
8. Replace VCM and reprogram. Perform VTD password relearn procedure and perform crankshaft variation learn procedure. See COMPUTER RELEARN PROCEDURES in GENERAL INFORMATION article. After repairs, go to step 3 .

FREQUENCY VS. RPM

Warning Light Circuit Diagnosis (3.4L)

1. Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. Go to next step.
2. Diagnose instrument cluster. See appropriate INSTRUMENT PANELS article in ACCESSORIES & EQUIPMENT. After diagnosis, go to next step.
3. Turn ignition off. Disconnect PCM harness connectors. Turn ignition on. Using DVOM, measure voltage between ground and affected PCM output circuit at PCM harness connector. See «CONTROL MODULE CONNECTOR TERMINAL IDENTIFICATION»(ref-9314-S19934600062000101800000) . See WIRING DIAGRAMS article. If battery voltage exists, go to next step. If battery voltage does not exist, go to step 7 .
4. Set DVOM to 10-amp scale. Using DVOM, measure current between ground and affected PCM output circuit at PCM harness connector. See «CONTROL MODULE CONNECTOR TERMINAL IDENTIFICATION»(ref-9314-S19934600062000101800000) . See WIRING DIAGRAMS article. Monitor current reading for about 2 minutes. If current is .05-1.5 amps, go to step 12 . If current is not .05-1.5 amps, go to next step.
5. Disconnect instrument cluster connector. Leave PCM harness connectors disconnected. Using DVOM, measure voltage between ground and affected PCM output circuit at instrument cluster connector. See WIRING DIAGRAMS article. If voltage is zero volts, go to step 15 . If voltage is not zero volts, go to next step.
6. Locate and repair short to voltage in affected PCM output circuit. After repairs, go to step 17 .
7. Check ignition feed fuse for instrument cluster indicator lights. If fuse is blown, go to next step. If fuse is okay, go to step 9 .
8. Locate and repair short to ground in ignition feed circuit for instrument cluster indicator lights. Replace fuse and go to step 17 .
9. Disconnect instrument cluster connector. Turn ignition on. Using DVOM, measure voltage between ground and ignition feed circuit at instrument cluster connector. See WIRING DIAGRAMS article. If battery voltage exists, go to next step. If battery voltage does not exist, go to step 14 .
10. Check for an open or short to ground in affected PCM output circuit. If problem exists, repair as necessary and go to step 17 . If problem does not exist, go to next step.
11. Check affected PCM output circuit and ignition feed circuit for poor connection at instrument cluster and at PCM. If problem exists, repair as necessary and go to step 17 . If problem does not exist, go to step 15 .
12. Turn ignition off. Reconnect PCM harness connector. Disconnect instrument cluster connector. Turn ignition on. Connect a test light between affected PCM output circuit and ignition feed circuit at instrument cluster connector. See WIRING DIAGRAMS article. Using scan tool, select OUTPUTS TEST, and cycle affected warning light on and off. If test light flashes on and off, check for shorted component or circuit in the output driver circuit. Check for faulty instrument cluster. If test light does not flash on and off, go to next step.
13. Check affected PCM output circuit for poor connection at PCM. If problem exists, repair as necessary and go to step 17 . If problem does not exist, go to step 16 .
14. Locate and repair open in ignition feed circuit to instrument cluster indicator lights. After repairs, go to step 17 .
15. Replace instrument cluster. After repairs, go to step 17 .
16. Replace PCM and reprogram. Perform VTD password relearn procedure and perform crankshaft variation learn procedure. See COMPUTER RELEARN PROCEDURES in GENERAL INFORMATION article. After repairs, go to next step.
17. Using scan tool, operate affected warning light. If warning light operates properly, system is okay. If warning light does not operate properly, go to step 2 .