Engine Controls - Basic Diagnostic Procedures - 5.7L: Diagnosis Chevrolet Tahoe I

VISUAL INSPECTION

Visually inspect all electrical wiring. Look for chafed, stretched, cut or pinched wiring. Ensure electrical connectors fit tightly and are not corroded. Ensure vacuum hoses are properly routed and not pinched or cut. If necessary, see VACUUM DIAGRAMS article to verify routing and connections. Inspect air induction system for possible vacuum leaks.

Diagnosis

1. Start engine and bring to operating temperature. Increase engine speed to 2000-2500 RPM and note gauge. If reading exceeds 1.25 psi (.09 kg/cm 2 ), exhaust system is restricted.
2. Check exhaust system for collapsed pipe, heat distress and possible internal muffler failure. If none of these conditions exist, check for restricted catalytic converter. Replace as required.

NO-START DIAGNOSIS

Note. For terminal and circuit ID, see the WIRING DIAGRAMS article.

General Inspection

1. Ensure proper starting procedure is being used. Visually check vacuum hoses for splits, kinks and proper connections, as shown on Vehicle Emission Control Information label. Check ignition wires for cracking, hardness and proper connections at both coil pack and spark plugs.
2. Remove spark plugs. Check and replace as necessary. In very cold temperatures, ensure oil is proper viscosity and not contaminated with gasoline.

FUEL SYSTEM PRESSURE TEST

INJECTOR CIRCUIT DIAGNOSIS

Note. This test only applies to vehicles equipped with a VCM.

1. Perform On-Board Diagnostic (OBD) System Check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-20660-S42057844782001010200000) . After performing OBD system check, go to next step.
2. Disconnect injector connector at intake manifold. Turn ignition on with engine off. Using test light connected to ground, probe ignition feed circuits. See the WIRING DIAGRAMS article. If test light illuminates, go to next step. If test light does not illuminate, go to step 7).
3. Install injector test light to each injector circuit, one at a time. Crank engine. If injector test light flashes on each injector, check fuel injector(s). See FUEL SYSTEM in the SYSTEM/COMPONENT TESTS article. If injector test light did not flash on an injector circuit, go to next step.
4. If injector test light was on steady on an injector circuit, go to next step. If injector test light did not illuminate on an injector circuit, go to step 6).
5. Install injector test light to affected injector. Turn ignition off. Disconnect Blue and Red VCM connectors. Turn ignition on with engine off. If injector test light turns off, go to step 11). If injector test light stays on, go to step 8).
6. Check for open or short in battery circuit to affected injector. If circuit is open or shorted, go to next step. If circuit is okay, go to step 9).
7. Repair circuit as necessary. After repairs, go to step 12).
8. Repair short to ground in injector control circuit. After repairs, go to step 12).
9. Check terminal contact at VCM connector. If terminal contact is faulty, go to next step. If terminal contact is okay, go to step 11).
10. Repair terminal contact. After repairs, go to step 12).
11. Replace VCM. Reprogram replacement VCM. After replacing VCM, go to next step.
12. Using scan tool, select DTC, CLEAR INFO function. Attempt to start engine. If engine starts and continues to run, go to next step. If engine does not start, or starts and stalls/dies, go to step 2).
13. Warm engine to normal operating temperature. Using scan tool, select DTC, FAILED THIS IGN function. If other DTC(s) are present, diagnose affected DTC(s). If no other DTC(s) are present, go to next step.
14. Using scan tool, select CAPTURE INFO, REVIEW INFO function. If additional undiagnosed DTC(s) are present, diagnose affected DTC(s). If DTC(s) are not present, system is okay.

ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK

Note. Use of Tech 1 scan tool is required to perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK .

The OBD System Check determines

1. If Malfunction Indicator Light (MIL) works.
2. If PCM/VCM is operating and can recognize a fault.
3. If any Diagnostic Trouble Codes (DTCs) are stored.

After performing procedures in PRELIMINARY INSPECTION & ADJUSTMENTS, BASIC FUEL SYSTEM CHECKS and BASIC IGNITION SYSTEM CHECKS, this is the starting point for utilizing the self-diagnostic system for determining computer-related problems. After performing necessary tests as described in the OBD system circuit check, if no codes are indicated and driveability problems still exist, see the TESTS W/O CODES article and SCAN TOOL usage in the TESTS W/CODES article.

1. Turn ignition on with engine off. Observe Malfunction Indicator Light (MIL). If MIL illuminates, go to next step. If MIL does not illuminate, go to «MALFUNCTION INDICATOR LIGHT (MIL)»(ref-20660-S40711401772001010200000) .
2. Turn ignition off. Install Tech 1 scan tool and follow scan tool manufacturer's instructions to proceed with test. Turn ignition on. If scan tool displays VCM data, go to next step. If scan tool does not display VCM data, go to «DLC DIAGNOSIS OR NO SCAN TOOL DATA»(ref-20660-S18699141782001010200000) .
3. Using scan tool, command MIL to turn off. If MIL turns off, go to next step. If MIL does not turn off, go to «MALFUNCTION INDICATOR LIGHT (MIL)»(ref-20660-S40711401772001010200000) .
4. Using scan tool, observe DTC status for MIL REQUEST, FAIL THIS IGN, LAST TST FAIL and HISTORY. If any DTC is stored, save freeze frame and fail record information using scan tool CAPTURE INFO feature. If any of these DTC status are present, refer to affected DTC to diagnose problem. If DTC(s) are not present, go to next step.
5. Crank engine for 10 seconds. If engine starts, go to next step. If engine does not start, go to «NO-START DIAGNOSIS»(ref-20660-S27054969302001010200000) .
6. Compare scan tool engine data with actual control system data values. If value is within limits, go to the TESTS W/O CODES article. If value is not within limits, go to the SYSTEM/COMPONENT TESTS article.

DLC DIAGNOSIS OR NO SCAN TOOL DATA

1. Perform On-Board Diagnostic (OBD) System Check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-20660-S42057844782001010200000) . After performing OBD system check, go to next step.
2. Using a test light connected to ground, probe DLC battery feed circuit. See the WIRING DIAGRAMS article. If test light illuminates, go to next step. If test light does not illuminate, go to step 11).
3. Using a test light connected to battery voltage, probe DLC ground circuit. See the WIRING DIAGRAMS article. If test light illuminates on both circuits, go to next step. If test light does not illuminate on both circuits, go to step 12).
4. Check cigarette lighter for power. If power is present at cigarette lighter, go to next step. If power is not present at cigarette lighter, go to step 13).
5. Install and check scan tool operation on another vehicle. If scan tool operates, go to next step. If scan tool does not operate, go to step 14).
6. Using DVOM connected to ground, measure voltage of DLC serial data line circuit. See the WIRING DIAGRAMS article. If voltage is less than 7 volts, go to next step. If voltage is more than 7 volts, go to step 16).
7. Using DVOM connected to ground, again measure voltage of DLC serial data line circuit. If voltage is less than one volt, go to next step. If voltage is more than one volt, go to step 16).
8. Turn ignition off. Using DVOM connected to ground, measure resistance of DLC serial data line circuit. If resistance is less than 10 milliohms, go to next step. If resistance is more than 10 milliohms, go to step 10).
9. Disconnect VCM connectors. Using DVOM connected to ground, measure resistance of DLC serial data line circuit. If resistance is less than 10 milliohms, go to step 17). If resistance is more than 10 milliohms, go to step 15).
10. Repair open in serial data line circuit. After repairs, go to step 18).
11. Repair open in DLC battery feed circuit. After repairs, go to step 18).
12. Repair open in circuit that did not cause test light to illuminate. After repairs, go to step 18).
13. Repair cigarette lighter. After repairs, go to step 18).
14. Repair or replace faulty scan tool and/or cables. After repairs, go to step 18).
15. Repair short to ground in serial data line circuit. After repairs, go to step 18).
16. Repair short to voltage in serial data line circuit. After repairs, go to step 18).
17. Replace VCM. Reprogram replacement VCM. After replacing VCM, go to next step.
18. Using scan tool, select DTC, CLEAR INFO function. Attempt to start engine. If engine starts and continues to run, go to next step. If engine does not start, or starts and dies/stalls, go to step 2).
19. Warm engine to normal operating temperature. Using scan tool, select DTC, FAILED THIS IGN function. If any DTC(s) are present, diagnose DTC. See the TESTS W/CODES article. If DTC(s) are not present, go to next step.
20. Select CAPTURE INFO, REVIEW INFO function. If additional DTC(s) are displayed, diagnose DTC. See the TESTS W/CODES article. If DTC(s) are not present, system is okay.