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

AIR INDUCTION SYSTEMS

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

TURBOCHARGER (6.5L DIESEL)

A malfunction in turbocharger boost system can set a related Diagnostic Trouble Code (DTC). For testing procedures, see appropriate SELF-DIAGNOSTICS article.

PCM POWER & GROUND CHECK

Note. To identify circuits referenced in the following ground and power tests, see WIRING DIAGRAMS article.

Ground Circuits

1. Using an ohmmeter, check for continuity to ground at PCM ground terminals. See «CONTROL MODULE CONNECTOR TERMINAL IDENTIFICATION»(ref-9314-S19934600062000101800000). see scheme 1- see scheme 4. Resistance should be zero ohms. If not, repair open to ground.
2. Using a voltmeter, connect negative lead of a voltmeter to a good ground. Backprobe positive lead of voltmeter to each ground terminal. With vehicle running, voltmeter should indicate less than one volt. If voltmeter reading is more than one volt, check for open, short to voltage, corrosion or loose connection on ground circuit.

Power Circuits

1. Using a voltmeter, check for battery voltage between PCM continuous power terminal(s) and ground. See «CONTROL MODULE CONNECTOR TERMINAL IDENTIFICATION»(ref-9314-S19934600062000101800000). see scheme 1- see scheme 4. If battery voltage is not present, check for open fuse or fusible link. If okay, check for open in wire between PCM terminal and power source.
2. Turn ignition switch to RUN position. Using a voltmeter, check for battery voltage between PCM ignition power terminals and ground. If battery voltage is not present, check IGN fuse. If fuse is okay, check for an open in wire between battery and ignition switch, and between ignition switch and PCM terminal. If wiring is okay, check for a defective ignition switch.
3. Connect voltmeter between ground and PCM starter (crank) signal terminal. On vehicles with manual transmission/transaxle, depress clutch pedal. On vehicles with automatic transmission/transaxle, position gear shift lever in Park. On all vehicles, turn ignition switch to START position. Battery voltage should be present ONLY when ignition switch is in START position.
4. If voltage is not present, check CRANK fuse or fusible link between ignition switch and PCM terminal. If fuse or fusible link is okay, check for an open in wire between ignition switch and PCM terminal, or check for a defective ignition switch.

ENGINE SENSORS & SWITCHES

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

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

Note. Ensure oil level is okay before performing engine oil level switch diagnosis.

ENGINE COOLANT TEMPERATURE SENSOR

A malfunction in Engine Coolant Temperature (ECT) sensor circuit can set a related Diagnostic Trouble Code (DTC). For testing procedure, see appropriate SELF-DIAGNOSTICS article. An out-of-calibration ECT sensor may not set a DTC. Use the following procedure to test sensor calibration.

Disconnect ECT sensor harness connector. Using an ohmmeter, measure resistance of ECT sensor at specified temperatures. See ECT SENSOR RESISTANCE VALUES table. Resistance should be high when engine is cold and drop as engine warms. With vehicle sitting overnight, IAT sensor and ECT sensor should have close to the same resistance reading. If resistance is not within specification, replace ECT sensor.

INTAKE AIR TEMPERATURE SENSOR

Note. Intake Air Temperature (IAT) sensor may also be referred to as Manifold Air Temperature (MAT) sensor.

A malfunction in IAT sensor circuit can set a related Diagnostic Trouble Code (DTC). For testing procedure, see appropriate SELF-DIAGNOSTICS article. An out-of-calibration IAT sensor may not set a DTC. Use the following procedure to test sensor calibration.

Disconnect IAT sensor harness connector. Using an ohmmeter, measure resistance of IAT sensor at specified temperatures. See IAT SENSOR RESISTANCE VALUES table. Resistance should be high when air temperature is cold and drop as air temperature warms. With vehicle sitting overnight, ECT sensor and IAT sensor should have close to the same resistance reading. If resistance is not within specification, replace IAT sensor.

MAP SENSOR CIRCUIT

Note. MAP sensor circuit diagnosis is only available from manufacturer for 2.2L (VIN 4) and 3.4L engines.

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 and retrieve DTCs. If no MAP sensor related DTCs are set, go to next step. If any MAP sensor related DTCs are set, perform appropriate DTC test. See appropriate SELF-DIAGNOSTICS article.
3. Turn ignition on with engine off. Compare MAP sensor reading with that of a known-good vehicle. If voltage readings are within 0.4 volt of each other, go to next step. If voltage readings are not within 0.4 volt of each other, go to step 5 .
4. Disconnect and plug vacuum source to MAP sensor. Connect a hand-held vacuum pump to vacuum source port on MAP sensor. Apply 10 in. Hg of vacuum to MAP sensor while observing MAP sensor reading on scan tool. Subtract this reading from the reading obtained in step 3 . If difference is greater than 1.5 volts, go to step 6 . If difference is not greater than 1.5 volts, go to step 7 .
5. Replace MAP sensor. After repairs, go to step 9 .
6. Check MAP sensor vacuum source for leakage or restriction, and that vacuum source only supplies MAP sensor. If problem exists, go to step 8 . If problem does not exist, go to step 9 .
7. Check for poor connection at MAP sensor. If poor connection does not exist, go to step 5 . If poor connection exists, repair as necessary and go to step 9 .
8. Repair leak or restriction in MAP sensor vacuum source as necessary. After repairs, go to next step.
9. Operate vehicle under conditions which original symptom was noted. If system operates properly, system is okay at this time. If system does not operate properly, go to step 2 .

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. Check for the following: Missing or damaged MAP sensor seal. Damage, disconnected or misrouted vacuum hoses. Intake manifold vacuum leaks. Vacuum leaks at throttle body. Vacuum leaks in EGR system. Faulty, missing or incorrectly installed PCV valve. If a problem does not exist, go to next step. If a problem exists, repair as necessary and go to step 14 .
3. Disconnect MAP sensor harness connector. Using scan tool, observe MAP sensor parameter. If zero volts is displayed, go to next step. If zero volts is not displayed, go to step 12 .
4. Using a test light connected to battery voltage, probe MAP sensor signal circuit (Light Green wire) at MAP sensor harness connector. See WIRING DIAGRAMS article. Observe MAP sensor parameter on scan tool. If 4.95 volts is displayed, go to next step. If 4.95 volts is not displayed, go to step 8 .
5. Using a fused jumper wire, connect MAP sensor signal circuit (Light Green wire) and MAP sensor reference voltage circuit (Gray wire) at MAP sensor harness connector. See WIRING DIAGRAMS article. Observe MAP sensor parameter on scan tool. If scan tool displays 4.95 volts, go to next step. If scan tool does not display 4.95 volts, go to step 7 .
6. Turn ignition off. Disconnect PCM harness connectors. Check MAP sensor ground circuit (Orange/Black wire) for open, high resistance or poor connection at PCM. If problem does not exist, go to step 10 . If problem exists, repair as necessary and go to step 14 .
7. Check MAP sensor reference voltage circuit (Gray wire) for open, high resistance or poor connection at PCM. If problem does not exist, go to step 9 . If problem exists, repair as necessary and go to step 14 .
8. Turn ignition off. Disconnect PCM harness connectors. Check MAP sensor signal circuit (Light Green wire) for open, high resistance, short to ground or short to sensor. If problem does not exist, go to next step. If problem exists, repair as necessary and go to step 14 .
9. Check MAP sensor signal circuit (Light Green wire) for poor connection at PCM. If problem does not exist, go to step 13 . If problem exists, repair as necessary and go to step 14 .
10. Check for poor connection at MAP sensor. If problem does not exist, go to next step. If problem exists, repair as necessary and go to step 14 .
11. Replace MAP sensor. After repairs, go to step 14 .
12. Turn ignition off. Disconnect PCM harness connector. Turn ignition on. Check MAP sensor signal circuit (Light Green) for a short to voltage or short to MAP sensor reference voltage circuit (Gray wire). If problem does not exist, go to next step. If problem exists, repair as necessary and go to step 14 .
13. 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.
14. Start engine and let idle. While observing MAP sensor parameter on scan tool, increase engine RPM. If MAP sensor value changes, system is okay. If MAP sensor value does not change, go to step 2 .

ENGINE OIL LEVEL SWITCH

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. Using scan tool, observe engine oil level display. If scan tool does not display OK, go to next step. If scan tool displays OK, check for poor connections at engine oil level switch and PCM. If poor connection exists, repair as necessary. If poor connection does not exist, perform warning light diagnosis. See «PCM CONTROLLED WARNING LIGHTS & GAUGES»(ref-9314-S37536557852000101700000) under MISCELLANEOUS CONTROLS.
3. Turn ignition off. Disconnect PCM harness connectors. Using a test light connected to battery voltage, probe engine oil level switch signal circuit (Brown wire) at PCM harness connector. If test light does not illuminate, go to next step. If test light illuminates, go to step 7 .
4. Ensure ignition is off. Reconnect PCM harness connectors. Turn ignition on. Raise and support vehicle. Disconnect engine oil level switch harness connector. Using DVOM, measure voltage between engine oil level switch harness connector terminals. If battery voltage does not exist, go to next step. If battery voltage exists, go to step 8 .
5. Using DVOM, measure voltage between chassis ground and engine oil level switch signal circuit (Brown wire) at engine oil level switch harness connector. If battery voltage does not exist, go to next step. If battery voltage exists, go to step 9 .
6. Check for open in engine oil level switch signal circuit (Brown wire) between engine oil level switch and PCM. If open exists, repair as necessary and go to step 12 . If open does not exist, check for poor connections at engine oil level switch and PCM. If poor connection exists, repair as necessary. If poor connection does not exist, perform warning light diagnosis. See «PCM CONTROLLED WARNING LIGHTS & GAUGES»(ref-9314-S37536557852000101700000) under MISCELLANEOUS CONTROLS.
7. Check for poor connections at PCM. If poor connection exists, repair as necessary and go to step 12 . If poor connection does not exist, go to step 11 .
8. Check for poor connections at engine oil level switch. If poor connection exists, repair as necessary and go to step 12 . If poor connection does not exist, go to step 10 .
9. Locate and repair open in engine oil level switch ground circuit (Black/White wire). After repairs, go to step 12 .
10. Replace engine oil level switch. After repairs, go to step 12 .
11. 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.
12. Start engine and allow to warm to normal operating temperature. Turn ignition off. Allow engine to cool for 15 minutes. Turn ignition on. Using scan tool, observe engine oil level display. If scan tool displays OK, system is okay. If scan tool does not display OK, go to step 3 .

MODULES, MOTORS, RELAYS & SOLENOIDS

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

A/C Compressor Clutch Relay

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

Fuel Pump Relay

Fuel pump relay is located in underhood fuse/relay block. To test fuel pump relay, see NO START DIAGNOSIS in appropriate BASIC DIAGNOSTIC PROCEDURES article.

EVAP Canister Purge Solenoid

See FUEL EVAPORATION under EMISSION SYSTEMS & SUB-SYSTEMS (GASOLINE).

Idle Air Control (IAC) Valve

See IDLE AIR CONTROL SYSTEM DIAGNOSIS under IDLE CONTROL SYSTEM.

FUEL SYSTEM (GASOLINE)

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

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

Fuel Pressure Regulator (CSI)

Fuel pressure regulator is a vacuum-controlled diaphragm type, which uses manifold vacuum to modify fuel pressure to compensate for engine load fuel requirements. Connect fuel pressure gauge to fuel pressure service port. Start engine and note fuel pressure. Disconnect vacuum hose from fuel pressure regulator. Fuel pressure should increase 4-10 psi (.28-.70 kg/cm 2 ). If pressure does not increase 4-10 psi (.28-.70 kg/cm 2 ), check for presence of manifold vacuum at signal line. If vacuum is not present, check for kinked, cut or split vacuum hose or plugged throttle body vacuum port. If vacuum is present and no pressure change occurs, replace fuel pressure regulator.

Fuel Pressure Regulator (SFI)

Fuel pressure regulator is mechanically controlled by internal spring pressure. Regulator is adjusted at factory and is not serviceable. If fuel pressure is too low, check for restricted delivery line. Also, check fuel pump pressure and volume. If fuel pressure is too high, check for restricted fuel tank return line or fuel filter. If no faults are found and pressure is too high or too low, replace fuel pressure regulator.

Fuel Pump Oil Pressure Switch (Back-Up Circuit)

To test fuel pump oil pressure switch (fuel pump back-up circuit), start engine. With engine running, disconnect fuel pump relay. If engine stalls, fuel pump oil pressure switch is faulty. If vehicle continues to run, switch is okay.

FUEL CONTROL

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

See RELAYS under MODULES, MOTORS, RELAYS & SOLENOIDS.

FUEL SYSTEM (DIESEL)

Note. Manufacturer does not provide testing procedures for many individual systems and component. For complete system testing and diagnosis, including fuel system testing not listed, see SELF-DIAGNOSTICS - DIESEL article.

Function Check

1. With ignition on, engine not running and at room temperature, glow plugs are on for 4-6 seconds, and then off for about 4.5 seconds. Following this on-and-off cycle, glow plugs are on for about one second and off for about 3 seconds. The glow plugs continue to cycle on and off in this time sequence for about 16 seconds.
2. If engine is cranked during or after the above sequence, glow plugs will cycle on and off for a total duration of 25 seconds after ignition switch is returned from crank position, whether engine starts or not. Engine does not have to be running to terminate glow plug cycling.

GLOW PLUG RELAY

1. Ensure coolant temperature is less than 80°F (27°C) before beginning test. Place ignition switch in RUN position and allow glow plugs to cycle. After 2 minutes, crank engine for one second. It is NOT important that engine starts. Return ignition switch to RUN position. Glow plugs should cycle on at least once.
2. If glow plugs do not cycle, disconnect glow plug relay (relay is located on top rear of engine). Connect test light between Pink wire terminal of harness connector and ground. With ignition switch in RUN position, test light should be off. Test light should illuminate when engine is cranked.
3. If test light does not illuminate as specified, repair short or open in engine harness Pink wire. If test light illuminates as specified but glow plugs do not cycle, replace glow plug relay.

FUEL GAUGE SELECTOR SWITCH/FUEL INDICATOR LIGHT

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. Turn ignition off for 30 seconds. Turn ignition on. Fuel Indicator Light (FIL), located on fuel gauge select switch should illuminate for 2 seconds (bulb check), then turn off. If FIL does not operate as specified, go to next step. If FIL operates as specified, go to step 9 .
3. If FIL stays on, go to next step. If FIL does not illuminate, go to step 6 .
4. Using scan tool, command AF ECU to turn FIL off. If FIL turns off, go to next step. If FIL does not turn off, go to step 8 .
5. Find cause of gasoline operation. Check for empty CNG tank, inaccurate fuel pressure sensor or AF ECU DTC. Repair as necessary. After repairs, go to step 22 .
6. Turn on instrument panel lights. Check fuel gauge select switch illumination. If illumination is okay, go to next step. If switch illumination does not work, go to step 11 .
7. Turn off instrument panel lights. Remove fuel gauge select switch. Disconnect 6-pin switch connector C239. Connect test light between harness connector terminals "D" (Purple wire) and "E" (Black wire). Turn ignition off for 30 seconds. Turn ignition on. If test light does not illuminate, go to step 12 . If test light illuminates, go to step 20 .
8. Turn ignition off for 30 seconds. Disconnect AF ECU connectors. Turn ignition on. If FIL illuminates, go to step 16 . If FIL does not illuminate, go to step 21 .
9. Connect scan tool. Using scan tool, monitor fuel gauge select switch input data. Press and release fuel gauge select switch. If scan tool data changed, go to next step. If scan tool data did not change, go to step 13 .
10. If fuel gauge is okay, test is complete. If fuel gauge is inaccurate or inoperative, check fuel gauge relay. See «FUEL GAUGE RELAY»(ref-9314-S24584807712000102600000) .
11. Remove fuel gauge select switch. Disconnect 6-pin switch connector C239. Connect test light between battery voltage and harness connector terminal "E" (Black wire). Turn ignition on. If test light does not illuminate, go to step 17 . If test light illuminates, go to step 20 .
12. Turn ignition off for 30 seconds. Disconnect AF ECU connectors. Check for open on Brown wire between fuel gauge select switch harness connector C239 terminal "C" and AF ECU connector C002 terminal No. 14. If open exists, go to step 18 . If circuit is okay, go to step 21 .
13. Remove fuel gauge select switch. Disconnect 6-pin switch connector C239. Connect test light between harness connector C239 terminal "A" (Red wire) and ground. Turn ignition on. If test light illuminates, go to next step. If test light does not illuminate, go to step 19 .
14. Using scan tool, monitor fuel gauge select switch input data. Connect a fused jumper wire between harness connector C239 "A" (Red wire) and "C" (Brown wire). If scan tool data did not change, go to next step. If scan tool data changed, go to step 20 .
15. Turn ignition off for 30 seconds. Disconnect AF ECU connectors. Check for open, short to voltage or poor contact on Brown wire between fuel gauge select switch harness connector C239 terminal "C" and AF ECU connector C002 terminal No. 14. If no problem is found, go to step 21 . If any problem is found, repair as necessary. After repairs, go to step 22 .
16. Replace internally shorted switch or repair short to power on Brown wire between fuel gauge select switch harness connector C239 terminal "C" and AF ECU connector C002 terminal No. 14. After repairs, go to step 22 .
17. Repair open circuit on Black wire between fuel gauge select switch harness connector C239 terminal "E" and ground. After repairs, go to step 22 .
18. Repair open or poor contact on Purple wire between fuel gauge select switch harness connector C239 terminal "D" and AF ECU connector C001 terminal No. 31. After repairs, go to step 22 .
19. Repair open on Red wire (power supply) at fuel gauge select switch harness connector C239 terminal "A". See WIRING DIAGRAMS article. After repairs, go to step 22 .
20. Replace fuel gauge select switch. After repairs, go to step 22 .
21. Replace AF ECU. After repairs, go to next step.
22. 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.

AF FUEL PUMP RELAY

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. Ensure both fuel systems are at least 1/4 full. Install CNG fuse (20-amp), if removed. Try to start engine. If engine does not start, go to next step. If engine starts, go to step 4 .
3. Turn ignition off for 30 seconds. Disconnect 2-pin fuel pump connector C019. Connect test light between fuel pump harness connector terminal "A" (Gray wire) and ground. Turn ignition on. If test light illuminates for 2 seconds, go to step 14 . If test light did not illuminate for 2 seconds, go to step 13 .
4. If vehicle operates on CNG, but not on gasoline, go to next step. If vehicle operates on both fuels, check CNG system. See ON BOARD DIAGNOSTIC (OBD) SYSTEM CHECK under SELF-DIAGNOSTIC SYSTEM in appropriate SELF-DIAGNOSTICS article.
5. Turn ignition off for 30 seconds. Using test light connected to ground, backprobe AF fuel pump relay terminal No. 30 (Gray wire). Turn ignition on. If test light illuminates for 2 seconds, go to next step. If test light does not illuminate, go to step 15 .
6. Start engine. Ensure vehicle is operating on CNG. Using test light connected to ground, backprobe AF fuel pump relay terminal No. 87A (Gray/Black wire). If test light does not illuminate, go to next step. If test light illuminates, go to step 8 .
7. Monitor test light while turning ignition off. If light stays on for 2 seconds after ignition is turned off, go to step 10 . If light does not stay on for 2 seconds after ignition is turned off, go to step 16 .
8. Start engine. Using test light connected to battery voltage, backprobe AF fuel pump relay terminal No. 86 (Black wire). If test light illuminates, go to next step. If test light does not illuminate, go to step 17 .
9. Using test light connected to ground, backprobe AF fuel pump relay terminal No. 85 (Brown wire). If test light illuminates, go to step 20 . If test light does not illuminate, go to step 18 .
10. Turn ignition off. Remove CNG fuse (20-amp) from underhood fuse block to force gasoline operation. Attempt to start engine. If engine does not operate on gasoline, go to next step. If engine operates on gasoline, check CNG operation. See ON BOARD DIAGNOSTIC (OBD) SYSTEM CHECK under SELF-DIAGNOSTIC SYSTEM in appropriate SELF-DIAGNOSTICS article.
11. Turn ignition off for 30 seconds. Disconnect 2-pin fuel pump connector C019. Connect a fused jumper wire between harness connector terminals. Attempt to start engine. If engine does not operate on gasoline, go to next step. If engine operates on gasoline, go to step 19 .
12. Repair problem in gasoline fuel delivery system. Check gasoline fuel pump, power circuit and ground circuit. See WIRING DIAGRAMS article. Repair as necessary. After repairs, go to step 22 .
13. Repair problem in gasoline fuel pump relay circuit. Check gasoline fuel pump relay, fuse, control circuit, power circuit and ground circuit. See WIRING DIAGRAMS article. Repair as necessary. After repairs, go to step 22 .
14. Check for open or poor contact on fuel pump power circuit (Gray wire) between fuel pump harness connector C019 terminal "A" and splice. See WIRING DIAGRAMS article. If no problem is found, diagnose no start condition. See appropriate BASIC DIAGNOSTIC PROCEDURES article. If any problem is found, repair as necessary. After repairs, go to step 22 .
15. Repair open on Gray wire between AF fuel pump relay terminal No. 30 and splice. See WIRING DIAGRAMS article. After repairs, go to step 22 .
16. Check AF fuel pump relay terminal contact. Check for short to battery voltage on control circuit (Brown wire). If no problem is found, go to step 20 . If any problem is found, repair as necessary. After repairs, go to step 22 .
17. Repair open circuit on Black wire between AF fuel pump relay terminal No. 86 and splice. See WIRING DIAGRAMS article. After repairs, go to step 22 .
18. Check for poor contact, open or short to ground on Brown wire between AF ECU connector C001 terminal No. 30 and AF fuel pump relay terminal No. 85. If no problem is found, go to step 21 . If any problem is found, repair as necessary. After repairs, go to step 22 .
19. Repair open circuit on Gray/Black wire between AF fuel pump relay terminal No. 87A and fuel pump connector C019 terminal "B". After repairs, go to step 22 .
20. Replace AF fuel pump relay. After repairs, go to step 22 .
21. Replace AF ECU. Program new AF ECU. After repairs, go to step 22 .
22. 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.

LOCK-OFF RELAY

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. Turn ignition off. Disconnect 2-pin Low Pressure Lock-Off (LPL) connector C014. Using test light connected to ground, probe LPL harness connector terminal "A" (Purple wire). Start engine. If test light illuminates, go to next step. If test light does not illuminate, go to step 6 .
3. Turn ignition off for 30 seconds. Turn ignition on. Using scan tool, clear AF ECU DTCs. Connect test light between LPL harness connector terminals "A" and "B". Monitor test light while cranking engine. If test light illuminates, go to next step. If test light does not illuminate, go to step 10 .
4. Turn ignition off. Remove fuel tank cover. Disconnect 2-pin High Pressure Lock-Off (HPL) connector C313. Using test light connected to ground, probe HPL harness connector terminal "A" (Purple wire). Start engine. If test light illuminates, go to next step. If test light does not illuminate, go to step 11 .
5. Turn ignition off for 30 seconds. Turn ignition on. Using scan tool, clear AF ECU DTCs. Connect test light between HPL harness connector terminals "A" and "B". Monitor test light while turning ignition on. If test light flashes, go to step 18 . If test light does not flash, go to step 10 .
6. Ensure engine is running. Using test light connected to ground, probe lock-off relay terminal No. 87 (Purple wire). If test light does not illuminate, go to next step. If test light illuminates, go to step 12 .
7. Turn ignition off. Remove lock-off relay. Start engine. Connect test light between relay connector terminals No. 85 (Gray wire) and No 86 (Black wire). If test light illuminates, go to next step. If test light does not illuminate, go to step 9 .
8. Ensure engine is running. Connect test light between relay connector terminal No. 30 (Orange wire) and ground. If test light illuminates, go to step 16 . If test light does not illuminate, go to step 13 .
9. Ensure engine is running. Connect test light between relay connector terminal No. 85 (Gray wire) and ground. If test light illuminates, go to step 14 . If test light does not illuminate, go to step 15 .
10. Check for poor contact or open circuit on Purple wire between relay and LPL or HPL. If no problem is found, go to step 17 . If any problem is found, repair as necessary. After repairs, go to step 18 .
11. Repair open Purple wire between HPL terminal "A" and splice. See WIRING DIAGRAMS article. After repairs, go to step 18 .
12. Repair open Purple wire between LPL terminal "A" and splice. See WIRING DIAGRAMS article. After repairs, go to step 18 .
13. Repair open Orange wire between relay terminal No. 30 and splice. See WIRING DIAGRAMS article. After repairs, go to step 18 .
14. Repair open Black wire between relay terminal No. 86 and ground. After repairs, go to step 18 .
15. Repair open Gray wire between relay terminal No. 85 and splice. See WIRING DIAGRAMS article. After repairs, go to step 18 .
16. Replace lock-off relay. After repairs, go to step 18 .
17. Replace AF ECU. Program AF ECU. After repairs, go to next step.
18. 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.

FUEL GAUGE RELAY

Note. To perform this test, vehicle must be operating on CNG.

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, command AF ECU fuel gauge output from full to empty. If gauge responds properly, go to next step. If gauge does not respond properly, go to step 6 .
3. Using scan tool, monitor VCM fuel level data. Depress and release fuel gauge select switch. Compare scan tool gasoline fuel level data to instrument cluster gauge. Gauge should display gasoline level, then return to CNG level display. If gauge is operating properly, go to next step. If gauge does not display properly, go to step 10 .
4. If CNG level is accurate, go to next step. If CNG level is inaccurate, diagnose CNG reading. See «CNG FUEL GAUGE READING INACCURATE»(ref-9314-S36359362002000102600000) .
5. If gasoline level is accurate, test is complete. If gasoline level is inaccurate, diagnose gauge. See appropriate ANALOG INSTRUMENT PANELS article in ACCESSORIES & EQUIPMENT.
6. Disconnect fuel gauge relay. Turn ignition on. Connect test light between relay connector terminals No. 85 (Black wire) and No. 86 (Gray wire). If test light illuminates, go to next step. If test light does not illuminate, go to step 12 .
7. Remove test light. Note gauge position. If gauge indicates past full, go to next step. If gauge does not indicate past full, go to step 13 .
8. Using a fused jumper wire, connect relay connector terminal No. 30 (Purple wire) to ground. If gauge moves to empty, go to next step. If gauge does not move to empty, go to step 14 .
9. Remove jumper wire from ground. Connect jumper wire between relay connector terminals No. 30 and No. 87 (Tan/White wire). Using scan tool, command AF ECU fuel gauge output from full to empty. If gauge does not indicate as commanded, go to step 15 . If gauge indicates as commanded, go to step 20 .
10. Remove fuel gauge relay. Connect test light between relay connector terminals No. 85 (Black wire) and No. 86 (Gray wire). If test light illuminates, go to next step. If test light does not illuminate, go to step 16 .
11. Remove test light. Connect jumper wire between relay connector terminals No. 30 (Purple wire) and No. 87 (Tan/White wire). Using scan tool, check VCM fuel level data. If gauge and scan tool do not match, go to step 17 . If gauge and scan tool match, go to step 20 .
12. Connect test light between relay connector terminal No. 85 (Black wire) and battery voltage. If test light illuminates, go to step 18 . If test light does not illuminate, go to step 19 .
13. Check Purple wire for short to ground or short to power (if jumper fuse blows). Repair as necessary. If no problem is found, repair instrument cluster. See appropriate ANALOG INSTRUMENT PANELS article in ACCESSORIES & EQUIPMENT. After repairs, go to step 22 .
14. Check Purple wire for open circuit or poor contact. Repair as necessary. If no problem is found, repair instrument cluster. See appropriate ANALOG INSTRUMENT PANELS article in ACCESSORIES & EQUIPMENT. After repairs, go to step 22 .
15. Check Tan/White wire for open, poor contact, short to power or short to ground. If no problem is found, go to step 21 . If problem is found, repair as necessary. After repairs, go to step 22 .
16. Check for short to power on Gray wire. If no problem is found, go to step 21 . If problem is found, repair as necessary. After repairs, go to step 22 .
17. Repair open, poor contact, short to power or short to ground on Purple/White wire between fuel gauge relay terminal No. 87A and connector C019 terminal "C" and Purple wire between connector C019 terminal "C" and VCM connector C1 terminal No. 9. After repairs, go to step 22 .
18. Check for open or short to ground on Gray wire. If no problem is found, go to step 21 . If problem is found, repair as necessary. After repairs, go to step 22 .
19. Repair open on Black wire between fuel gauge relay terminal No. 85 and splice S009. After repairs, go to step 22 .
20. Replace fuel gauge relay. After repairs, go to step 22 .
21. Replace AF ECU and reprogram. After repairs, go to next step.
22. 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.

CNG FUEL GAUGE READING INACCURATE

1. Perform «FUEL GAUGE SELECTOR SWITCH/FUEL INDICATOR LIGHT»(ref-9314-S30531723182000102600000) and «FUEL GAUGE RELAY»(ref-9314-S24584807712000102600000). Go to next step.
2. Using scan tool, check AF ECU data. If Fuel Temperature Sensor (FTS) and Intake Air Temperature (IAT) sensor data are within 35° F (20°C), go to next step. If FTS and IAT data is not within 35° F (20°C), go to step 10.
3. Using scan tool, monitor fuel pressure sensor data. Connect vehicle to CNG filling station. Fill tank. If FPS and filling station pressures are the same, go to next step. If pressures are not the same, go to step 6.
4. Check CNG tank pressure and temperature. Determine percentage full. (Scheme 10) If calculated percentage and fuel gauge reading are not the same, go to next step. If calculated percentage and fuel gauge reading are the same, check system. See «FUEL SYSTEM DIAGNOSIS (ALTERNATIVE FUEL)»(ref-9314-S33519839542000102400000).
5. Using DVOM connected to ground, backprobe fuel gauge relay terminal No. 30 (Purple wire). Measure Pulse Width Modulated (PWM) signal. Compare expected PWM output to actual output. See «FUEL LEVEL/PWM OUTPUT»(ref-9314-S39530973002000103000000) table. If PWM is as expected, go to step 13. If PWM is not as expected, go to step 14.
6. Turn ignition off. Remove fuel tank cover. Disconnect 3-pin Fuel Pressure Sensor (FPS) connector. Turn ignition on. Using scan tool, check FPS data. If FPS data is more than 4.9 volts, go to next step. If FPS data is 4.9 volts or less, go to step 15.
7. Check reference voltage at FPS harness connector terminal "B" (Orange wire). If 4.7-5.2 volts exists, go to next step. If 4.7-5.2 volts does not exist, go to step 16.
8. Remove DVOM. Using a fused jumper wire, connect FPS harness connector terminal "A" (Dark Blue wire) to terminal "C" (Gray wire). If fuse blows, repair short to power on Gray wire and recheck system. Using scan tool, check FPS data. If FPS data is.20 volt or more, go to next step. If FPS data is less than.20 volt, go to step 19.
9. Using test light connected to battery voltage, probe FPS harness connector terminal "A" (Dark Blue wire). If test light illuminates, go to step 17. If test light does not illuminate, go to step 18.
10. Turn ignition off. Remove fuel tank cover. Disconnect 3-pin Fuel Pressure Sensor (FPS) connector. Turn ignition on. Using scan tool, check FPS data. If FPS data is more than 4.9 volts, go to next step. If FPS data is 4.9 volts or less, go to step 15.
11. Using a fused jumper wire, connect FPS harness connector terminal "A" (Dark Blue wire) to terminal "C" (Gray wire). If fuse blows, repair short to power on Gray wire and recheck system. Using scan tool, check FPS data. If FPS data is.20 volt or more, go to next step. If FPS data is less than.20 volt, go to step 20.
12. Using test light connected to battery voltage, probe FPS harness connector terminal "A" (Dark Blue wire). If test light illuminates, go to step 17. If test light does not illuminate, go to step 18.
13. Check for open, poor contact or short on Purple wire between fuel gauge relay terminal No. 30 and instrument cluster terminal No. 16.. If no problem is found, diagnose instrument cluster. See appropriate ANALOG INSTRUMENT PANELS article in ACCESSORIES & EQUIPMENT. If problem is found, repair as necessary. After repairs, go to step 22.
14. Check for open, short or high resistance on Tan/White wire between fuel gauge relay terminal No. 87 and AF ECU connector C001 terminal No. 8. If no problem is found, go to step 21. If problem is found, repair as necessary. After repairs, go to step 22.
15. Check for short to ground on Gray wire between FPS connector terminal "B" and AF ECU connector C001 terminal No. 24. If no problem is found, go to step 21. If problem is found, repair as necessary. After repairs, go to step 22.
16. Check for open or short to ground (less than 4.7 volts) and short to power (more than 5.2 volts) on Orange wire between FPS harness connector terminal "B" and AF ECU connector C002 terminal No. 18. If no problem is found, go to step 21. If problem is found, repair as necessary. After repairs, go to step 22.
17. Check for open or poor contact on Gray wire between FPS connector terminal "B" and AF ECU connector C001 terminal No. 24. If no problem is found, go to step 21. If problem is found, repair as necessary. After repairs, go to step 22.
18. Check for open or poor contact in Dark Blue wire between FPS connector terminal "A" and AF ECU connector C002 terminal No. 19. If no problem is found, go to step 21. If problem is found, repair as necessary. After repairs, go to step 22.
19. Replace fuel pressure sensor. After repairs, go to step 22.
20. FTS is faulty. Replace high pressure lock-off solenoid. After repairs, go to step 22.
21. Replace AF ECU and reprogram. After repairs, go to next step.
22. 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.

Scheme 10

FUEL LEVEL/PWM OUTPUT

IDLE CONTROL SYSTEM

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

IGNITION SYSTEM

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

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

IGNITION RELAY (CNG)

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. Check CNG and IGN E fuses, located in underhood fuse block. If fuses are okay, go to next step. If one or both fuses are faulty, go to step 14 .
3. Turn ignition on. Using test light connected to ground, probe both sides of each fuse. If test light does not illuminate at all terminals, go to next step. If test light illuminates at all terminals, go to step 5 .
4. Check fuse contacts and power source. See WIRING DIAGRAMS article. Repair as necessary. After repairs, go to step 23 .
5. Using scan tool, attempt to communicate with AF ECU. If AF ECU does not communicate, go to next step. If scan tool communicates, go to step 8 .
6. Turn ignition off. Disconnect AF ECU connectors. Turn ignition on. Using test light connected to ground, probe AF ECU connector C002 terminals No. 15 (Pink wire) and No. 16 (Orange wire). If test light illuminates at both terminals, go to next step. If test light does not illuminate at both terminals, go to step 15 .
7. Using test light connected to battery voltage, probe AF ECU connector C002 terminals No. 21, 22, 23 and 24 (Black wire). If test light does not illuminate at all terminals, go to step 15 . If test light illuminates at all terminals, go to step 21 .
8. Turn ignition off for 30 seconds. Monitor Fuel Indicator Light (FIL), located on fuel gauge select switch. Turn ignition on. If FIL does not illuminate, go to next step. If FIL illuminates, go to step 10 .
9. Turn ignition on. Using test light connected to ground, backprobe ignition relay terminal No. 87 (Red wire). If test light does not illuminate, go to step 11 . If test light illuminates, diagnose fuel gauge select switch light. See «FUEL GAUGE SELECTOR SWITCH/FUEL INDICATOR LIGHT»(ref-9314-S30531723182000102600000) .
10. Using test light connected to ground, backprobe ignition relay terminal No. 87 (Red wire). Turn ignition off. If test light stays on, go to step 16 . If test light does not stay on, recheck system. See ON BOARD DIAGNOSTIC (OBD) SYSTEM CHECK under SELF-DIAGNOSTIC SYSTEM in appropriate SELF-DIAGNOSTICS article.
11. Backprobe ignition relay terminal No. 30 (Orange wire). If test light illuminates, go to next step. If test light does not illuminate, go to step 17 .
12. Ensure ignition is on. Backprobe ignition relay terminal No. 85 (Pink wire). If test light illuminates, go to next step. If test light does not illuminate, go to step 18 .
13. Remove ignition relay. Connect test light between relay connector terminal No. 85 (Pink wire) and No. 86 (Black wire). If test light illuminates, go to step 20 . If test light does not illuminate, go to step 19 .
14. Diagnose and repair short causing fuse to blow. See WIRING DIAGRAMS article. After repairs, go to step 23 .
15. Repair open circuit. After repairs, go to step 23 .
16. Replace ignition relay or repair short to power on Pink wire. After repairs, go to step 23 .
17. Repair open circuit on Orange wire. After repairs, go to step 23 .
18. Repair open circuit on Pink wire. After repairs, go to step 23 .
19. Repair open on Black wire. After repairs, go to step 23 .
20. Replace ignition relay. After repairs, go to step 23 .
21. Check AF ECU terminal contact. If no problem is found, go to next step. If any problem is found, repair as necessary. After repairs, go to step 23 .
22. Replace AF ECU. Program AF ECU. Go to next step.
23. 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.

Ignition Control Circuit (Gasoline Engines)

An open or short to ground in Ignition Control (IC) or by-pass circuit will cause PCM to turn on Malfunction Indicator Light (MIL) and confirm fault by setting a related DTC. See appropriate SELF-DIAGNOSTICS article.

Knock Sensor Circuit (Models Using External Spark Controller Module)

1. An open or short circuit on IC module control wire to PCM will cause a loss of 12-volt IC module signal. This will cause PCM to fully retard ignition timing.
2. Install scan tool. Using a metal object, tap on engine next to knock sensor and note knock parameter. Knock should be indicated on scan tool.
3. If a scan tool is not available, backprobe PCM knock sensor signal terminal with a DVOM. With engine idling, 8-12 volts should be present at this terminal. Using a metal object, tap on engine close to knock sensor. Voltage signal at PCM terminal should drop to zero volts, and then return to original voltage when knock signal ceases.
4. If voltage signal does not respond as described, check knock sensor-to-module signal. On vehicles equipped with automatic transmission, it may be necessary to place transmission in Drive for timing change to occur.

Knock Sensor Circuit (Models Using Knock Sensor With Internal Spark Controller Module)

1. An open or short circuit on knock sensor wire to PCM will set a related DTC. A false detonation signal will not cause PCM to set a DTC.
2. Install scan tool. Using a metal object, tap on engine next to knock sensor and note knock parameter. Knock should be indicated on scan tool.
3. If a scan tool is not available, connect tachometer to engine. Start engine and hold RPM above idle. Using a metal object, tap on engine close to knock sensor. A noticeable decrease in engine RPM should occur. If no RPM decrease occurred, check knock sensor-to-PCM circuit.
4. On vehicles equipped with automatic transmission, it may be necessary to place transmission in Drive for timing change to occur.

EMISSION SYSTEMS & SUB-SYSTEMS (GASOLINE)

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

FUEL EVAPORATION

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

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

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

Required Service

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

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

A leaking PCV valve or hose could cause

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

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

Checking PCV Valve Function

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

EMISSION SYSTEMS & SUB-SYSTEMS (DIESEL)

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

Crankcase Depression Regulator (CDR) Valve

To test CDR valve, connect one end of a water manometer to engine oil dipstick tube. Leave other end of manometer open to atmosphere. Unplug rubber vent tube from turbo inlet elbow. Install air cleaner and run engine. CDR valve specification is one in. H 2 O at idle to 3-4 in. H 2 O at full load. Add amount of distance water travels down one side of gauge to distance water travels up other side of gauge to obtain reading.

EGR Valve Check

With engine off, disconnect vacuum hose to EGR valve. Connect vacuum pump to EGR and apply 10 in. Hg. vacuum. EGR diaphragm should move up and stay up for at least 20 seconds. If EGR does not operate as specified, replace EGR valve.

VACUUM PUMP

Connect vacuum gauge to vacuum pump inlet (small fitting). DO NOT plug or disconnect outlet fitting. With engine idling, vacuum should be 18 in. Hg one minute after start. If vacuum is not as specified, check for belt slippage, vacuum leaks or other obvious defects. If no defects are present, replace vacuum pump.

MISCELLANEOUS CONTROLS

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

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

A/C COMPRESSOR CLUTCH CONTROLS

Note. For A/C compressor clutch circuit testing, see appropriate AUTOMATIC A/C-HEATER SYSTEMS or MANUAL A/C-HEATER SYSTEMS article in AIR CONDITIONING & HEATING. See WIRING DIAGRAMS article for terminal and wire color identification.

ELECTRIC COOLING FAN CONTROL

Note. For electric cooling fan circuit testing, see ELECTRIC COOLING FANS article in AIR CONDITIONING & HEATING. See WIRING DIAGRAMS article for terminal and wire color identification.

TRANSMISSION

Note. Computerized transmission controls are also covered in greater detail in appropriate ELECTRONIC CONTROLS article in AUTOMATIC TRANSMISSIONS. For component circuit identification, see WIRING DIAGRAMS article.