Engine Controls - System & Component Testing - 6.5L: 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.

PRELIMINARY GLOW PLUG DIAGNOSIS

1. If system does not operate as described in «NORMAL GLOW PLUG CIRCUIT OPERATION»(ref-20720-S34831079172001010300000) , 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 panel for tight connection and proper operation.

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 ready for use. 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. CAUTION: Use Nozzle Socket (J-29873) to remove and replace injection nozzle. Attach socket to 30-mm hex portion of nozzle. Failure to do so will result in damage to injector nozzle.
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 that does not meet lowest acceptable pressure. Release tester pressure.

Leakage Test

1. Open tester shutoff valve 3/4 to 1 3/4 turns from closed position. Blow dry injector nozzle tip. Slowly depress tester lever until pressure gauge reads 1400 psi (98 kg/cm 2 ). Maintain pressure for 10 seconds and observe injector nozzle tip.
2. A drop may form on end of injector nozzle, but should not fall off within a 10 second period. Replace injector nozzle if a drop of test fluid falls from tip during 10 second period. (Scheme 28) Release tester pressure.

Scheme 28

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 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.

Warning Light Diagnosis

1. Perform On-Board Diagnostics (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in the «BASIC TESTING - 6.5L DIESEL»(ref-20661) 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 - 6.5L DIESEL»(ref-20661) 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 - 6.5L»(ref-20682) 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.