Engine Control System & Component Tests - 5.7L: Diagnosis Chevrolet Tahoe I

A/C ON SWITCH/SYSTEM TEST

1. Turn ignition switch to RUN position. Move mode selector switch to any position other than OFF position. With A/C control assembly connected, measure voltage between mode selector switch Light Green wire and ground. For wiring schematics, see the WIRING DIAGRAMS article.
2. Battery voltage should be present. If battery voltage is present, mode selector switch is operating normally. If battery voltage is not present, check wire from mode selector switch to fuse for an open circuit. Also check A/C high and low pressure switches for open.
3. Check voltage between mode selector switch Dark Green/White wire or Light Green wire and ground. Voltage should not be present. If voltage is present, replace mode selector switch.

Central Sequential Port Injector Balance Test (CSI)

Note. Central Sequential Port Injector Balance Test has been revised due to Technical Service Bulletin (TSB) 61-63-16, dated February, 1997. See SMU - SECTION 6E - REVISED INJECTOR BALANCE TEST .

The injector balance test is used to pulse the injector for a precise amount of time, spraying a measured amount of fuel in the intake manifold. As each injector is pulsed, a drop in fuel rail pressure occurs. This pressure drop can be recorded and compared to other injectors. All injector should have the same pressure drop of 1.5 psi (.11 kg/cm 2 ).

Note. Allow engine to cool to avoid irregular readings due to "hot soak" fuel boiling. To prevent flooding, INJECTOR BALANCE TEST should not be repeated more than once without starting and running engine.

1. Perform on-board diagnostics. Check for Diagnostic Trouble Code (DTC). If DTC(s) are present, diagnose DTC first. If DTC(s) are not present, go to next step.
2. Turn ignition off. Connect Fuel Pressure Gauge (J-39021-301) to pressure tap. Unplug injector harness connector. Connect Injector Switch Box (J-39021-210). Turn ignition on. Monitor fuel gauge. Fuel pressure should be 60-66 psi (4.2-4.6 kg/cm 2 ). If pressure is as specified, go to step 3). If pressure is not as specified, check fuel pump and fuel lines for restriction.
3. Run fuel pump for at least 2 seconds after ignition is turned on. Energize injectors one at a time. Note fuel pressure for each injector. Fuel pressure should drop about 1.5 psi (.11 kg/cm 2 ) on each injector. If fuel pressure drop is as specified, go to next step. If fuel pressure drop is not as specified, perform injector coil test. See INJECTOR COIL TEST (CSI).
4. Remove upper manifold assembly. Connect Poppet Nozzle Tester (J-34730-230). Connect a fused jumper wire (10-amp) to fuel pump test connector. Energize each injector one at a time, fuel should spray from each poppet nozzle tester. If fuel did not spray from an injector, go to next step.
5. Replace faulty injector and poppet nozzle assembly. After replacing injector and poppet nozzle assembly, go to next step.
6. Install Tech 1 scan tool. Select DTC, CLEAR INFO. Start engine. If engine starts and continues to run, go to next step. If engine does not start or starts and dies, repeat step 2).
7. Warm engine to normal operating temperature. Select DTC, FAILED THIS IGN. If additional DTC(s) are displayed, diagnose DTC. If DTC(s) are not present, go to next step.
8. Using scan tool, select CAPTURE INFO, REVIEW INFO. If additional DTC(s) are present, diagnose DTC. If DTC(s) are not present at this time, system is okay.

Injector Coil Test (CSI)

1. Perform on-board diagnostic test. Diagnose any Diagnostic Trouble Code (DTC) present. If DTC is not present, go to next step.
2. Turn ignition off. Relieve fuel pressure. Connect Fuel Injector Tester (J-39021) to battery positive. Connect Injector Switch Box (J-39021-210). Set amperage on fuel injector tester to 0.5 amp. Connect DVOM to fuel injector tester. Connect Tech 1 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. Perform this test to 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 CENTRAL SEQUENTIAL PORT INJECTOR BALANCE TEST (CSI).
5. Replace faulty injector nozzle and poppet assembly and then proceed to next step.
6. Using Tech 1 scan tool, select DTC, CLEAR INFO. Start engine. If engine starts and continues to run, go to next step. If engine does not start or starts and dies, repeat step 2).
7. Warm engine to normal operating temperature. Using scan tool, select DTC, FAILED THIS IGN. If DTC(s) are present, diagnose DTC(s). If DTC(s) are not present, go to next step.
8. Using scan tool, select CAPTURE INFO, REVIEW INFO. If additional DTC(s) are present, diagnose DTC(s). If DTC(s) are not present, system is okay.

CIRCUIT DESCRIPTION

System includes a distributor, ignition coil, ignition control module, secondary wires, spark plugs, VCM and crank sensor. Ignition system is controlled by Vehicle Control Module (VCM). The VCM monitors the information from various engine sensors, computes the desired spark timing and controls the dwell and firing of the ignition coil via an (IC) line to the ignition control module.

Diagnostic Aids

Note. Numbers below refer to the step numbers in diagnostic test.

Note. Battery should be fully charged prior to any tests.

1. 1 Perform the OBD system check before proceeding unless it was already performed.
2. 2 Checks for proper output from the enhanced ignition system. The spark tester requires a minimum of 25,000 volts to operate. This check can be used in case of an ignition miss, because the system may provicle enough voltage to run the engine but not enough to operate a spark plug under heavy load.
3. 3 This test separates distributor cap, rotor and ignition wires from ignition coil in order to help identify a secondary ignition system problem.
4. 5 - This test checks ignition control module, connections, and wiring.
5. 12 - This test begins to determine if the VCM is providing a signal to the ignition control module. If the VCM is not providing a signal to the ignition control module, the problem exists between the ignition control module and the VCM.
6. 14 - This test checks for a basic engine mechanical problem.

Warning Light Diagnosis

1. Perform On-Board Diagnostics (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in the «BASIC TESTING - 5.7L»(ref-20660) article. After performing OBD system check, go to next step.
2. Check instrument cluster. See the INSTRUMENT PANEL article in the ACCESSORIES/SAFETY EQUIPMENT section. If instrument panel is okay, go to next step.
3. Turn ignition off. Disconnect PCM connector. Turn ignition on. Using a DVOM, check voltage between affected PCM output circuit at PCM harness connector terminal and ground. See the WIRING DIAGRAMS article. Battery voltage should be present. If battery voltage is present, go to next step. If battery voltage was not present, go to step 7).
4. Set DVOM to 10-amp scale. Check current between affected PCM output circuit and ground. Monitor reading for about 2 minutes. DVOM should read .05-1.50 amps. If reading is as specified, go to step 12). If reading is not as specified, go to next step.
5. Disconnect instrument cluster, leaving PCM connector disconnected. Using DVOM, check voltage between affected PCM output circuit and ground. DVOM should read zero volts. If voltage reading is as specified, go to step 15). If voltage reading is not as specified, 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. Check voltage between ignition feed circuit for instrument cluster indicator lights and ground. Battery voltage should be present. If battery voltage is present, go to next step. If battery voltage was not present, go to step 14).
10. Check affected PCM output circuit for an open or shorted circuit to ground. If circuit is open or shorted, go to step 17). If circuit was okay, 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 is present, repair as necessary and then go to step 17). If problem was not found, 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 panel harness connector. Using a scan tool, perform OUTPUTS TEST function to 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 to PCM. Replace defective terminal and then go to step 17). If terminal is okay, go to step 16).
14. Repair open in ignition feed circuit to instrument cluster indicator lights. After repairs, go to step 17).
15. Replace instrument cluster and then go to step 17).
16. Replace PCM and then go to next step.
17. Using scan tool, operate affected warning light. If warning light does not operate properly, go to step 3).

Tachometer Control Circuit Diagnosis

1. Diagnose instrument cluster. See the INSTRUMENT PANEL article in the ACCESSORIES/SAFETY EQUIPMENT section. After diagnosis, go to next step.
2. Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in the «BASIC TESTING - 5.7L»(ref-20660) article. After performing OBD system check, go to next step.
3. Turn ignition off. Disconnect PCM connector. Turn ignition on. Using a DVOM, check voltage between tachometer control circuit at PCM harness connector terminal and ground. See the WIRING DIAGRAMS article. Battery voltage should be present. If battery voltage is present, go to next step. If battery voltage was not present, go to step 7).
4. Set DVOM to 10-amp scale. Check current between tachometer control circuit and ground. Monitor reading for about 2 minutes. DVOM should read .05-1.50 amps. If reading is not as specified, go to next step. If reading is as specified, go to step 12).
5. Disconnect instrument cluster, leaving PCM connector disconnected. Using DVOM, check voltage between tachometer control circuit and ground. DVOM should read zero volts. If voltage reading is as specified, go to step 15). If voltage reading is not as specified, go to next step.
6. Locate and repair short to voltage in tachometer control circuit. After repairs, go to step 17).
7. Check ignition feed fuse for instrument cluster. 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 to instrument cluster. Replace fuse and go to step 17).
9. Disconnect instrument cluster connector. Turn ignition on. Check voltage between ignition feed circuit for instrument cluster and ground. Battery voltage should be present. If battery voltage was not present, go to step 14). If battery voltage is present, go to next step.
10. Check tachometer control circuit for an open or shorted circuit to ground. If circuit is open or shorted, go to step 17). If circuit was okay, go to next step.
11. Check tachometer control circuit and ignition feed circuit for poor connection at instrument cluster and at PCM. If problem is present, repair as necessary and then go to step 17). If problem was not found, go to step 15).
12. Turn ignition off. Reconnect PCM harness connector. Disconnect instrument cluster connector. Turn ignition on. Connect a test light between tachometer control circuit and ignition feed circuit at instrument panel harness connector. Using a scan tool, perform OUTPUTS TEST function to cycle tachometer control output 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 flash on and off, go to next step.
13. Check tachometer control circuit for poor connection to PCM. Replace defective terminal and then go to step 17). If terminal is okay, go to step 16).
14. Repair open in ignition feed circuit to instrument cluster. After repairs, go to step 17).
15. Replace instrument cluster and then go to step 17).
16. Replace PCM and then go to next step.
17. Start engine and observe tachometer. If tachometer does not operate properly, diagnose instrument cluster. See the INSTRUMENT PANEL article in the ACCESSORIES/SAFETY EQUIPMENT section.

Compressor Clutch Control Circuit Diagnosis

1. Install A/C manifold gauge set. Ensure A/C system is fully charged. Charge system if necessary and go to next step.
2. Start engine and allow it to reach normal operating temperature. Turn on A/C. If A/C compressor clutch engages, then disengages within 60 seconds, diagnose A/C-heater system. If operation is not as specified, go to next step.
3. Install scan tool. With A/C on, monitor A/C REQUEST. If scan tool displays A/C REQUEST as YES, go to next step. If scan tool does not display A/C REQUEST as YES, go to step 8).
4. Disconnect A/C compressor clutch harness connector. Connect a test light between harness connector terminals. If test light comes on, go to next step. If test light does not come on, go to step 12).
5. Check for faulty A/C compressor clutch harness connections. If a problem is found, go to next step. If no problem is found, go to step 7).
6. Repair faulty A/C compressor clutch wire harness connections. Go to step 27).
7. Replace A/C compressor clutch. Go to step 27).
8. Turn ignition off. Disconnect VCM harness connectors. Turn ignition on. Using a test light connected to ground, probe A/C request circuit (Dark Green/White wire) at VCM harness connector. If test light comes on, go to next step. If test light does not come on, go to step 11).
9. Check for poor VCM harness connections. If a problem is found, go to next step. If no problem is found, go to step 26).
10. Repair VCM harness connector. Go to step 27).
11. Repair open or short to ground in Dark Green/White wire between VCM and A/C control switch. Go to step 27).
12. Using a test light connected to ground, probe Dark Green wire at A/C compressor clutch harness connector. If test light comes on, go to next step. If test light does not come on, go to step 14).
13. Repair open in A/C compressor clutch ground circuit (Black wire) between harness connector and ground. Go to step 27).
14. Turn ignition on, engine off. Using scan tool, command A/C relay on. If A/C relay clicks, go to step 23). If A/C relay does not click, go to next step.
15. Disconnect A/C relay. Using a test light connected to ground, probe A/C relay cavity No. 86 (Pink wire), then cavity No. 87 (Orange wire). If test light comes on for both wires, go to step 17). If test light does not come on for both wires, go to next step.
16. Repair open or short to ground in affected circuit. Go to step 27).
17. Connect a test light between A/C relay cavity No. 86 (Pink wire) and cavity No. 85 (Dark Green/White wire). Using scan tool, command A/C relay on. If test light comes on, go to next step. If test light does not come on, go to step 19).
18. Replace A/C relay. Go to step 27).
19. Check A/C relay control circuit (Dark Green/White wire) for faulty connection at VCM harness connector. If a problem is found, go to next step. If no problem is found, go to step 21).
20. Repair faulty connection at VCM. Go to step 27).
21. Check for open in Dark Green/White wire between VCM and A/C relay. If a problem is found, go to next step. If no problem is found, go to step 26).
22. Repair open in Dark Green/White wire. Go to step 27).
23. Remove A/C relay. Using a fused jumper wire, jumper A/C relay cavity No. 87 (Orange wire) and cavity No. 30 (Dark Green wire) together. If A/C compressor clutch engages, go to next step. If A/C compressor clutch does not engage, go to step 25).
24. Replace A/C relay. Go to step 27).
25. Repair open or short to ground in A/C compressor clutch control circuit (Dark Green wire). Go to step 27).
26. Replace VCM. Go to next step.
27. Using scan tool, select DTC CLEAR INFO. Start engine and allow it to reach normal operating temperature. Select DTC SPECIFIC, then enter DTC number that was set. Operate vehicle within conditions that may have set this DTC. If DTC does not reset, go to next step. If DTC resets, go to step 2).
28. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any DTCs are displayed that have not been diagnosed, perform diagnosis for applicable DTC. See the «TESTS W/CODES - 5.7L»(ref-20681) article. If no DTCs are displayed, system is okay.

Cooling Fan Circuit Diagnosis

1. If cooling fan does not run, go to next step. If cooling fan runs continuously, go to step 9).
2. Remove cooling fan relay from harness connector. Using a test light connected to ground, probe cooling fan relay harness connector terminal No. 30. If test light comes on, go to next step. If test light does not come on, locate and repair open or short to ground in circuit No. 1540 (Orange wire) between AUX FAN fuse (30-amp) and cooling fan relay.
3. Turn ignition on. With test light still connected to ground, probe cooling fan relay harness connector terminal No. 85. If test light comes on, go to next step. If test light does not come on, locate and repair open or short to ground in circuit No. 1240 (Orange wire) between A/C COMP fuse (10-amp) and cooling fan relay.
4. Using a fused jumper wire, jumper cooling fan relay harness connector terminals No. 30 and 87 together. If cooling fan does not run, go to next step. If cooling fan runs, go to step 6).
5. Turn ignition off. Disconnect cooling fan motor harness connector. Using an ohmmeter, check for continuity between harness connector terminal "A" and ground. If continuity is present, locate and repair open in circuit No. 702 (Red wire) between cooling fan relay and cooling fan motor. If continuity is not present, locate and repair open or poor connection in circuit No. 250 (Black wire) between cooling fan motor and ground.
6. Turn ignition off. Disconnect VCM harness connector C4. Using an ohmmeter, check for continuity between VCM harness connector C4, terminal No. 6 and cooling fan relay harness connector terminal No. 86. If continuity is present, go to next step. If continuity is not present, locate and repair open in circuit No. 473 (Dark Blue wire) between cooling fan relay and VCM.
7. Reconnect cooling fan relay. Turn ignition on. Using a fused jumper wire, jumper VCM harness connector C4, terminal No. 6 to ground. If cooling fan runs, go to next step. If cooling fan does not run, replace cooling fan relay.
8. Using a test light connected to battery positive, probe VCM harness connector C4, terminal No. 7. Push REC button on A/C control panel to ON position. If test light comes on, check VCM harness connector for corroded, backed-out or poorly connected terminal pins. Repair as necessary. If connections are okay, VCM is faulty.
9. Turn ignition on. Disconnect cooling fan relay from harness connector. If cooling fan motor stops, go to next step. If cooling fan motor continues to run, locate and repair short to power in circuit No. 702 (Red wire) between cooling fan relay and cooling fan motor.
10. Turn ignition off. Disconnect VCM harness connector C4. Using an ohmmeter, check for continuity between VCM harness connector C4, terminal No. 6 and ground. If continuity is not present, go to next step. If continuity is present, locate and repair short to ground in circuit No. 473 (Dark Blue wire) between cooling fan relay and ground.
11. Ensure ignition is off. Ensure REC button on A/C control panel is in OFF position. Using an ohmmeter, check for continuity between VCM harness connector C4, terminal No. 7 and ground. If continuity is present, locate and repair short to ground in circuit No. 1614 (Dark Green wire) between A/C control module and VCM. If continuity is not present, replace cooling fan relay.

1. If cooling fan does not operate, or does not operate properly, go to next step. If cooling fan runs continuously with ignition off, go to step 12). If cooling fan runs continuously with ignition on, go to step 13).
2. If cooling fan motor never operates, go to next step. If cooling fan motor does not operate with high coolant temperature, go to step 9). If cooling fan motor does not operate with A/C on, go to step 10).
3. Turn ignition off. Disconnect fan control relay harness connector. Turn ignition on. Using a test light connected to ground, probe fan control relay harness connector terminal No. 30. If test light comes on, go to next step. If test light does not come on, locate and repair open in Red wire between fan control relay and splice near fusible link.
4. Using a fused jumper wire, jumper fan control relay harness connector terminals No. 30 and 87 together. If cooling fan motor runs, go to next step. If cooling fan motor does not run, go to step 6).
5. Disconnect jumper wire. Using a test light connected to ground, probe fan control relay harness connector terminal No. 85. If test light comes on, go to step 8). If test light does not come on, locate and repair open in Pink wire between ENG 1 fuse and fan control relay.
6. With jumper wire still in place, disconnect cooling fan motor harness connector. Using a test light connected to ground, probe cooling fan motor harness connector terminal "B". If test light comes on, go to next step. If test light does not come on, locate and repair open in Red wire between fan control relay and cooling fan motor.
7. Using a test light connected to battery positive, probe cooling fan motor harness connector terminal "A". If test light comes on, replace cooling fan motor. If test light does not come on, locate and repair open in Black wire between cooling fan motor and ground.
8. Reconnect fan control relay. Using a voltmeter, measure voltage (backprobe) between fan control relay harness connector terminal No. 86 and ground. If reading is less than 10 volts, replace fan control relay. If reading is 10 volts or greater, locate and repair open in Dark Green wire between fan control relay and splice.
9. Disconnect auxiliary fan control switch harness connector. Turn ignition on. Using a voltmeter, measure voltage between auxiliary fan control switch harness connector terminal "A" and ground. If reading is less than 10 volts, locate and repair open in Dark Green wire between auxiliary fan control switch and splice. If reading is 10 volts or greater, replace auxiliary fan control switch.
10. Disconnect A/C high pressure switch harness connector. Using a voltmeter, measure voltage between auxiliary fan control switch harness connector terminal "B" and ground. If reading is 10 volts or greater, go to next step. If reading is less than 10 volts, locate and repair open in Dark Green wire between A/C high pressure fan switch and splice.
11. Using a test light connected to battery positive, probe A/C high pressure switch harness connector terminal "A". If test light comes on, replace A/C high pressure fan switch. If test light does not come on, locate and repair open in Black wire between A/C high pressure switch harness connector terminal "A" and splice.
12. With ignition on, disconnect fan control relay harness connector. If cooling fan motor stops, replace fan control relay. If cooling fan motor continues to run, locate and repair short to power in Red wire between fan control relay and cooling fan motor.
13. Turn ignition off. Disconnect fan control relay harness connector. Using a test light connected to battery positive, probe cooling fan relay harness connector terminal No. 86. If test light comes on, go to next step. If test light does not come on, replace fan control relay.
14. With test light still connected, disconnect auxiliary fan control switch harness connector. If test light remains on, go to next step. If test light does not remain on, replace auxiliary fan control switch.
15. With test light still connected, disconnect A/C high pressure fan switch harness connector. If test light remains on, locate and repair short to ground in Dark Green wire between fan control relay and either A/C high pressure fan switch or auxiliary fan control switch.