Engine Controls - System & Component Testing Chevrolet Blazer S15 рестайлинг

MODEL IDENTIFICATION

Note. System and component testing is not available for 3.4L (VIN E) "A" & "B" Series, 4.3L (VIN W) "C" & "K" Series, 6.6L (VIN 1) "C" & "K" Series, 8.1L (VIN G) "C" & "K" Series and 8.1L (VIN G) "G" Series. Component locations are available for all models. See COMPONENT LOCATIONS .

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

MODEL IDENTIFICATION

INTRODUCTION

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

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

AIR INDUCTION SYSTEMS

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

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 OUTPUT DIAGNOSIS (2.2L)

1. Perform powertrain diagnostic system check. See POWERTRAIN DIAGNOSTIC SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. After performing powertrain diagnostic system check, go to next step.
2. 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»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-system-component-testing__diagnostic-aids) .

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.

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. 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. 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.

PCM Harness Resistance

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

ENGINE SENSORS & SWITCHES

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

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.

ECT SENSOR RESISTANCE VALUES

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.

IAT SENSOR RESISTANCE VALUES

MAP SENSOR CIRCUIT

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

2.2L

1. Perform powertrain diagnostic system check. See POWERTRAIN DIAGNOSTIC SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. After performing powertrain diagnostic system check, go to next step.
2. Install scan tool 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 powertrain diagnostic system check. See POWERTRAIN DIAGNOSTIC SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. After performing powertrain diagnostic system check, go to next step.
2. Check for the following: 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 powertrain diagnostic system check. See POWERTRAIN DIAGNOSTIC SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. After performing powertrain diagnostic system check, go to next step.
2. 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»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-system-component-testing) 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»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-system-component-testing) 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.

Torque Converter Clutch (TCC) Solenoid

See TRANSMISSION under MISCELLANEOUS CONTROLS.

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.

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

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

1. Perform powertrain diagnostic system check. See POWERTRAIN DIAGNOSTIC SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. After performing powertrain diagnostic system check, go to next step.
2. 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)»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-system-component-testing__injector-coil-test-except-22l) .
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 & 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 powertrain diagnostic system check. See POWERTRAIN DIAGNOSTIC SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. After performing powertrain diagnostic system check, go to next step.
2. 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 powertrain diagnostic system check. See POWERTRAIN DIAGNOSTIC SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. After performing powertrain diagnostic system check, go to next step.
2. 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 and 6.0L, 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 and 6.0L, 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)»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-system-component-testing__injector-coil-test-except-22l) .

Injector Coil Test (Except 2.2L & 3.4L)

1. Perform powertrain diagnostic system check. See POWERTRAIN DIAGNOSTIC SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. After performing powertrain diagnostic system check, go to next step.
2. 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)»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-system-component-testing__injector-balance-test-except-22l) .
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)

1. Perform powertrain diagnostic system check. See POWERTRAIN DIAGNOSTIC SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. After performing powertrain diagnostic system check, go to next step.
2. Install scan tool. 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)»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-system-component-testing__injector-coil-test-ect-is) .
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 & 3.4L)»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-system-component-testing__injector-balance-test-22l-34l) .
4. Replace faulty injector(s). After repairs, perform injector balance test. See «INJECTOR BALANCE TEST (2.2L & 3.4L)»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-system-component-testing__injector-balance-test-22l-34l) .

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

1. Perform powertrain diagnostic system check. See POWERTRAIN DIAGNOSTIC SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. After performing powertrain diagnostic system check, go to next step.
2. Install scan tool. 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)»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-system-component-testing__injector-coil-test-ect-is) .
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 & 3.4L)»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-system-component-testing__injector-balance-test-22l-34l) .
4. Replace faulty injector(s). After repairs, perform injector balance test. See «INJECTOR BALANCE TEST (2.2L & 3.4L)»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-system-component-testing__injector-balance-test-22l-34l) .

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

1. Perform powertrain diagnostic system check. See POWERTRAIN DIAGNOSTIC SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. After performing powertrain diagnostic system check, go to next step.
2. Install scan tool. 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)»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-system-component-testing__injector-coil-test-ect-is) .
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 & 3.4L)»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-system-component-testing__injector-balance-test-22l-34l) .
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 & 3.4L)»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-system-component-testing__injector-balance-test-22l-34l) .

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

1. Perform powertrain diagnostic system check. See POWERTRAIN DIAGNOSTIC SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. After performing powertrain diagnostic system check, go to next step.
2. Install scan tool. 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)»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-system-component-testing__injector-coil-test-ect-is) .
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 & 3.4L)»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-system-component-testing__injector-balance-test-22l-34l) .
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 & 3.4L)»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-system-component-testing__injector-balance-test-22l-34l) .

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.

Supply System

The fuel flows through a pre-filter screen in the tank and to the engine through the fuel supply lines. There is no lift pump in the fuel tanks or on the frame. The fuel passes through the base plate of the fuel injector control module (FICM) to cool the module. From the FICM the fuel flows to the fuel filter assembly, which combines a water separator, a prime pump and a filter element. Within the assembly, there is also a fuel heater. An integrated hand pump is used to prime the fuel system after changing the fuel filter or servicing the fuel system. The fuel injection pump at the front of the engine valley includes a fuel supply pump and a high-pressure pump. Fuel is drawn to the supply pump from the primary fuel tank by the supply pump and delivered to the high-pressure pump.

High Pressure System

The much larger section of the pump assembly is the high-pressure fuel injection pump. The pump is engine-driven by the camshaft gear. From the high-pressure pump, the fuel flows through the junction block. The junction block routes pressurized fuel to both common fuel rails. Each common fuel rail supplies one bank of four fuel injectors.

Return System (Fuel Return System Volume Test)

The Fuel Return System routes fuel from the fuel injectors, the junction block, and the fuel injection pump. The return fuel travels to the fuel cooler and then to the fuel tank. This fuel is used to cool and lubricate the injection pump and the injectors

1. Were you Referred here from one of the following diagnostics? DTC P0094 Surges/Chuggles in Symptoms Rough, Unstable, or Incorrect Idle in Symptoms Fuel Injector Balance Test with Tech 2 If you answered Yes, go to the Fuel Pressure Regulator Graphing after step 48. If you answered No, go to Step 2.
2. Remove the air duct from the air cleaner assembly and the turbo inlet.
3. Remove the air intake pipe.
4. Drain the coolant and remove the water outlet tube
5. Remove the fuel injection pump fuel return rubber hose from the junction block (2). Cap the fitting on the block with a 3/8 inch rubber cap (1) to prevent fuel leakage
6. Attach a rubber hose (1) with a barbed fitting to the fuel injection pump return hose and insert the other end into a 1 gallon clean fuel container (2).
7. Remove the ignition 1 relay or EDU relay, as equipped, using the J 43244 Relay Puller Pliers
8. Remove the glow plug harness bracket bolt.
9. Remove the glow plug harness bracket nut from the valve cover
10. Remove the glow plug controller/relay mounting nuts
11. Reposition the glow plug controller/relay
12. Remove the fuel line retainers
13. Remove the banjo bolt (2) from left rear cylinder head
14. Install the black hose (1) of the J 45873 to the left rear cylinder head and install the other end of the hose into one of the J 45873 graduated cylinders.
15. Remove the banjo bolt (3) from the leak-off block
16. Install the other black hose (1) of the J 45873 to the leak--off block (2) and install the other end of the hose into another J 45873 graduated cylinders
17. Remove the banjo bolt (4) from the junction block (2).
18. Crank the engine for 15 seconds while observing the fuel pressure relief valve on the junction block for fuel leakage If fuel is leaking from the fuel pressure relief valve, replace the fuel pressure relief valve. If no fuel is leaking from the fuel pressure relief valve, go to step 19
19. Crank the engine in 15 second intervals, with one minute cooling time between, until fuel starts to flow into one or both of the J 45873 graduated cylinders (1).
20. Elevate the hoses (2) to retain the fuel in the hoses, and empty the graduated cylinders into a suitable container
21. Install the hoses (2) into 2 of the graduated cylinders (1). IMPORTANT: The engine cranking speed must be more than 150 RPM
22. Crank the engine for 15 seconds
23. Measure the quantity of fuel in each of the graduated cylinders. Refer to «FUEL SYSTEM SPECIFICATIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-system-component-testing) for fuel return flow specifications. If there is more than the specified quantity of fuel from either cylinder bank, remove the valve cover from that bank, then go to step 24 If there is less than the specified quantity from each cylinder bank, replace the fuel injection pump and repeat steps 19-23 If the fuel injection pump has already been replaced in this repair and there is less than the specified quantity of fuel from each bank, go to step 45 IMPORTANT: When the fuel injector pressure lines are removed, debris will fall into the fuel injector inlet fitting. Vacuum the debris from the inlet fitting of the fuel injector.
24. Remove the return line from injectors
25. Install the four yellow hoses (2) from the J 45873 to the injectors (1) and the other end of the hoses into each of the J 45873 graduated cylinders
26. Install the four injector supply lines. Tighten the supply lines to 44 Nm (32 lb ft).
27. Connect the engine-to-chassis harness connectors to enable the starter
28. Install the fuel filter hoses, FICM hoses, and the fuel supply hose. Push the fuel supply hose in until it locks
29. Install the black hoses from the J 45873 into the container that the fuel injection pump return hose is in. Prime the fuel system 30 times to remove air from the fuel system. Air will be forced out of the system within 2 minutes
30. Crank the engine in 15 second intervals, with one minute cooling time between, until fuel starts to flow into one or more of the graduated cylinders
31. Elevate the four hoses to retain the fuel in the hoses, and empty the 4 graduated cylinders into a suitable container
32. Install the hoses in the graduated cylinders in numerical order IMPORTANT: The engine cranking speed must be more than 150 RPM
33. Crank the engine for 15 seconds IMPORTANT: A fuel injector may have high fuel return flow only at higher engine temperatures. If the high return flow ceases between the bank return flow test and the individual injector return flow test the fuel injectors may need to be heated to an operating temperature before performing this test
34. Measure the quantity of fuel in each of the graduated cylinders. Refer to «FUEL SYSTEM SPECIFICATIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-system-component-testing) for fuel return flow specifications. Remove the fuel feed pipes from any injectors that have high return fuel flow, and install the EN 47589 fuel pressure adapter cap(s) to the fuel rail outlets. Then go to step 35.
35. Repeat steps 30 through 34 until no fuel injectors have more than the specified quantity of fuel flow
36. Were both banks of fuel injectors tested with steps 30 through 35? If the answer is YES, go to step 44 If the answer is NO, go to step 37.
37. Ensure that the hoses are still installed as they were in steps 14 through 17.
38. Prime the fuel system 30 times to remove the air from the fuel system. Air will be forced out of the system within 2 minutes
39. Crank the engine in 15 second intervals, with one minute cooling time between, until fuel starts to flow into one or both of the J 45873 graduated cylinders (1).
40. Elevate the hoses (2) to retain the fuel in the hoses, and empty the graduated cylinders into a suitable container
41. Install the hoses (2) into 2 of the graduated cylinders (1). IMPORTANT: The engine cranking speed must be more than 150 RPM.
42. Crank the engine for 15 seconds
43. Measure the quantity of fuel in each of the graduated cylinders. Refer to «FUEL SYSTEM SPECIFICATIONS»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-system-component-testing) for fuel return flow specifications. If there is more than the specified quantity of fuel in either of the 2 cylinders, remove the valve cover from that cylinder head, then perform steps 29 through 35 on the bank of fuel injectors with the high fuel flow, then go to step 44. If both of the cylinder have less than the specified quantity of fuel, go to step 44
44. Replace all of the fuel injectors that had fuel rail outlets capped.
45. Install all disconnected and removed components. Refer to the applicable procedures
46. Start and idle the engine. You may have to prime the fuel system before the engine will start
47. Connect a scan tool
48. Command the fuel pressure control to 160 MPa with a scan tool If the fuel pressure is more than 145 MPa, the system is OK. If the fuel pressure is unable to increase to more than 145 MPa, replace the fuel injection pump.

Fuel Pressure Regulator Graphing

1. Set up the scan tool in the following format: 1.1 Select the Data Display on the scan tool 1.2 Select Engine Data 1 1.3 Select the More softkey 2 times 1.4 Select the Live Plot softkey 1.5 Select the Engine Speed, Actual Fuel Rail Pressure, and Desired Fuel Rail Pressure parameters by highlighting each parameter and depressing the ENTER softkey 1.6 Select the Accept softkey 1.7 Select the More softkey, then select the Change Min/Max softkey 1.8 Select the More softkey, and adjust the parameters to the following Min/Max ranges: The Engine Speed Min/Max range is 0 to 1000 RPM The Actual Fuel Rail Pressure Min/Max range is 1.0 to 160 MPa The Desired Fuel Rail Pressure Min/Max range is 1.0 to 160 MPa
2. Start and idle the engine
3. Observe the live plot for sharp changes in the Actual Fuel Rail Pressure above and below the Desired fuel rail pressure while performing one of the following actions: Idling the engine. Shifting the transmission from Park to Drive, and back to Park Turning the steering wheel from lock to lock Turning the air conditioning ON and OFF
4. If there is a violent fluctuation in the Actual Fuel Rail pressure, as seen in the third Graphic above, replace the fuel pressure regulator.

What Fuel to Use in the United States

In the United States, for best results use Number 2-D diesel fuel year-round, above and below freezing conditions, as oil companies blend Number 2-D fuel to address climate differences. Number 1-D diesel fuel may be used in very cold temperatures when the temperature stays below -18°C (0°F). However, the fuel will produce a power and fuel economy loss. The use of Number 1-D diesel fuel in warm or hot climates may result in stalling, poor starting when the engine is hot and may damage the fuel injection system.

Diesel fuel may foam when filling the tank. This can cause the automatic pump nozzle to shut OFF, even though the tank is not full. If this happens, just wait for the foaming to stop and then continue to fill the tank

What Fuel to Use in Canada

Canadian fuels are blended for seasonal changes. Diesel Type A fuel is blended for better cold weather starting (when it stays below -18°C (0°F). However, the fuel will produce a power and fuel economy loss. The use of Type A diesel fuel in warmer climates may result in stalling, poor starting. Diesel Type B fuel is blended for temperatures above -18°C (0°F). The emission control system requires the use of diesel fuel with low sulfur, 0.05 percent by weight , content. Both low and higher sulfur fuels will be available in Canada. Only low sulfur diesel fuels are available in the United States. Diesel-powered trucks must be refueled only with low sulfur fuel. Use of fuels with higher-sulfur content will affect the function of the emission components and may caused reduced performance, excessive smoke and unpleasant odor

Very Cold Weather Operation

If the vehicle is driven in very cold temperatures and can not get a winterized Number 2-D that has been adapted to cold weather or a Number 1-D, use one gallon of kerosene for every two gallons of diesel fuel. Once you add kerosene, run the engine for several minutes to mix the fuels. Only add kerosene when the temperature falls below -18°C (0°F), because the fuel economy and lubricating qualities of kerosene is not as good as that of diesel fuel

In cold weather , the fuel filter may become clogged (waxed). To unclog the filter, move the vehicle to a warm garage area and warm the filter to a temperature between 0-10°C (32-50°F). Replacing the filter is not necessary

Fuel Specific Gravity Testing

Use a J 38641-B Diesel Fuel Quality Tester to measure the fuel specific gravity (API Rating). Follow the instructions on the tool to btain the proper temerpature-adjusted value. This information must be accurate for the proper diagnosis of the fuel system.

Fuel Injector Return Flow and Fuel Pressures

The fuel return from the fuel injectors to the tank will vary based on the API value of the fuel. Measure the Fuel API with the Diesel Fuel Quality Tester. For this reason the Fuel System Diagnosis-High Pressure Side values will vary for identifying a fuel injector or fuel pump concern. Use the following tables when referred to by the diagnostic. The first table is to be used during the initial diagnosis to identify the worst fuel injectors. After the fuel injectors that fail the first part of the test are replaced, the return flow from each fuel injector must be measured again. This is because the fuel system is returning less fuel to the tank, and thus the fuel pressure is higher during the retest. Failure to use the correct table may result in the replacement of good fuel injectors.

INITIAL FUEL INJECTOR RETURN FLOW VALUES

RETESTING FUEL INJECTOR RETURN FLOW VALUES

Water in Fuel

Sometimes, water can be pumped into the fuel tank along with diesel fuel. This can happen if the service station does not regularly inspect and clean their fuel tanks, or the fuel gets contaminated for the service stations suppliers.

If water is pumped into the fuel tank, a water in fuel light will illuminate. If the water in fuel light illuminates, the excess water must be drained from the fuel system on the vehicle.

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.

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»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-system-component-testing__function-check) , 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»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-system-component-testing__water-in-fuel-light-diagnosis) .
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. see scheme 19 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. see scheme 19 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 10

GLOW PLUG SYSTEM DIAGNOSIS

1. Perform powertrain diagnostic system check. See POWERTRAIN DIAGNOSTIC SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. After performing powertrain diagnostic system check, go to next step.
2. 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 .

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.

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. see scheme 20 Release tester pressure.

Scheme 11

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»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-system-component-testing__lock-off-relay) .
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»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-system-component-testing__lock-off-relay) .
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»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-system-component-testing__fuel-gauge-selector-switchfuel-indicator-light) .
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)»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-system-component-testing) , 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»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-system-component-testing__cng-fuel-gauge-reading-inaccurate) .
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.

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»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-system-component-testing__fuel-gauge-relay) .
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.

ALTERNATIVE FUEL (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»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-system-component-testing__cng-fuel-gauge-reading-inaccurate) .
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»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-system-component-testing__fuel-gauge-selector-switchfuel-indicator-light) and «FUEL GAUGE RELAY»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-system-component-testing__fuel-gauge-relay). 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. see scheme 21 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)»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-system-component-testing).
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»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-system-component-testing) 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 12

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.

IDLE AIR CONTROL SYSTEM DIAGNOSIS

1. Perform powertrain diagnostic system check. See POWERTRAIN DIAGNOSTIC SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. After performing powertrain diagnostic system check, go to next step.
2. 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". see scheme 22 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". see scheme 22 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 13

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»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-system-component-testing__fuel-gauge-selector-switchfuel-indicator-light) .
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.

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 powertrain diagnostic system check. See POWERTRAIN DIAGNOSTIC SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. After performing powertrain diagnostic system check, go to next step.
2. Install scan tool. 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 .

EGR System Diagnosis

1. Perform powertrain diagnostic system check. See POWERTRAIN DIAGNOSTIC SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. After performing powertrain diagnostic system check, go to next step.
2. 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. see scheme 23 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. see scheme 23 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. see scheme 23 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. see scheme 23 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. see scheme 23 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. see scheme 23 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. see scheme 23 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 14

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.

EVAP Control System Diagnosis (2.2L)

1. Perform powertrain diagnostic system check. See POWERTRAIN DIAGNOSTIC SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. After performing powertrain diagnostic system check, go to next step.
2. Install scan tool. Turn ignition on 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)»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-system-component-testing__pcm-output-diagnosis-22l) 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 powertrain diagnostic system check. See POWERTRAIN DIAGNOSTIC SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. After performing powertrain diagnostic system check, go to next step.
2. 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 powertrain diagnostic system check. See POWERTRAIN DIAGNOSTIC SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. After performing powertrain diagnostic system check, go to next step.
2. 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 powertrain diagnostic system check. See POWERTRAIN DIAGNOSTIC SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. After performing powertrain diagnostic system check, go to next step.
2. 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 .

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.

Generator Circuit Diagnosis (2.2L)

1. Perform powertrain diagnostic system check. See POWERTRAIN DIAGNOSTIC SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. After performing powertrain diagnostic system check, go to next step.
2. 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 powertrain diagnostic system check. See POWERTRAIN DIAGNOSTIC SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. After performing powertrain diagnostic system check, go to next step.
2. 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 powertrain diagnostic system check. See POWERTRAIN DIAGNOSTIC SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. After performing powertrain diagnostic system check, go to next step.
2. Install scan tool. 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»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-system-component-testing) 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 powertrain diagnostic system check. See POWERTRAIN DIAGNOSTIC SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. After performing powertrain diagnostic system check, go to next step.
2. 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 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 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 .

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.

Note. Some TCC solenoids have an internal pressure switch in series with solenoid winding and will not show continuity until transmission hydraulic pressure is applied.

Disconnect Torque Converter Clutch (TCC) solenoid harness connector. Using DVOM, measure resistance between appropriate TCC solenoid terminals. Solenoid resistance should be greater than 20 ohms.

Torque Converter Lock-Up Signal At Transmission

1. Warm engine to operating temperature. Raise vehicle and support drive wheels. Support suspension where necessary to prevent damage to drive axles.
2. Disconnect torque converter clutch harness connector at transmission. Connect a test light between appropriate torque converter clutch harness connector terminals. Start engine and place transmission in Drive. Accelerate vehicle to 45 MPH and note test light.
3. If test light does not illuminate, check for open or short to ground in solenoid power supply circuit of torque converter clutch harness connector. Also, check for open in ground circuit between torque converter clutch harness connector and PCM. If circuit is okay, see «TORQUE CONVERTER LOCK-UP SIGNAL FROM PCM»(/chevrolet/blazer/s15-1998-2005/remont/testing-diagnostics/#engine-controls-system-component-testing__torque-converter-lock-up-signal-from-pcm) .

Torque Converter Lock-Up Signal From PCM

1. Warm engine to operating temperature. Raise vehicle and support drive wheels. Support suspension where necessary to prevent damage to drive axles.
2. Connect a test light to battery voltage. Touch TCC control driver terminal with test light. Accelerate vehicle to 45 MPH and note test light. If test light does not illuminate, problem is a faulty PCM connector or PCM.

COMPONENT LOCATIONS 2.2L (VIN 5) "S" SERIES

COMPONENT LOCATIONS 2.2L (VIN 5) "S" SERIES

COMPONENT LOCATIONS 3.4L (VIN E) "A" & "B" SERIES

COMPONENT LOCATIONS 3.4L (VIN E) "A" & "B" SERIES

COMPONENT LOCATIONS 3.4L (VIN E) "U" SERIES

COMPONENT LOCATIONS 3.4L (VIN E) "U" SERIES

COMPONENT LOCATIONS 4.3L (VIN W) "C" & "K" SERIES

COMPONENT LOCATIONS 4.3L (VIN W) "C" & "K" SERIES

COMPONENT LOCATIONS 4.3L (VIN W) "G" SERIES

COMPONENT LOCATIONS 4.3L (VIN W) "G" SERIES

COMPONENT LOCATIONS 4.3L (VIN W) "L" & "M" SERIES

COMPONENT LOCATIONS 4.3L (VIN W) "L" & "M" SERIES

COMPONENT LOCATIONS 4.3L (VIN W) "S" & "T" SERIES

COMPONENT LOCATIONS 4.3L (VIN W) "S" & "T" SERIES

COMPONENT LOCATIONS 4.8L (VIN V), 5.3L (VIN T) & 6.0L (VIN U) "C" & "K" SERIES

COMPONENT LOCATIONS 4.8L (VIN V), 5.3L (VIN T) & 6.0L (VIN U) "C" & "K" SERIES

COMPONENT LOCATIONS 5.0L (VIN M) & 5.7L (VIN R) "G" SERIES

COMPONENT LOCATIONS 5.0L (VIN M) & 5.7L (VIN R) "G" SERIES

COMPONENT LOCATIONS 6.5L (VIN F) "C" & "K" SERIES

COMPONENT LOCATIONS 6.5L (VIN F) "C" & "K" SERIES

COMPONENT LOCATIONS 6.5L (VIN F) "G" SERIES

COMPONENT LOCATIONS 6.5L (VIN F) "G" SERIES

COMPONENT LOCATIONS 6.6L (VIN 1) "C" & "K" SERIES

COMPONENT LOCATIONS 6.6L (VIN 1) "C" & "K" SERIES

COMPONENT LOCATIONS 8.1L (VIN G) "C" & "K" SERIES

COMPONENT LOCATIONS 8.1L (VIN G) "C" & "K" SERIES

COMPONENT LOCATIONS 8.1L (VIN G) "G" SERIES

COMPONENT LOCATIONS 8.1L (VIN G) "G" SERIES

See also:
• COMPONENT LOCATIONS
• DIAGNOSTIC AIDS
• FUEL EVAPORATION
• IDLE AIR CONTROL SYSTEM DIAGNOSIS
• TRANSMISSION
• INJECTOR COIL TEST (EXCEPT 2.2L & 3.4L)
• INJECTOR BALANCE TEST (EXCEPT 2.2L & 3.4L)
• INJECTOR COIL TEST - ECT IS NOT 50-95°F (2.2L)
• INJECTOR BALANCE TEST (2.2L & 3.4L)
• NORMAL GLOW PLUG CIRCUIT OPERATION
• WATER-IN-FUEL LIGHT DIAGNOSIS
• LOCK-OFF RELAY
• FUEL GAUGE SELECTOR SWITCH/FUEL INDICATOR LIGHT
• CNG FUEL GAUGE READING INACCURATE
• FUEL GAUGE RELAY
• PCM OUTPUT DIAGNOSIS (2.2L)
• TORQUE CONVERTER LOCK-UP SIGNAL FROM PCM