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

Compression

Check engine mechanical condition with a compression gauge, vacuum gauge, or an engine analyzer. See engine analyzer manual for specific instructions. For compression specifications, see the SPECIFICATIONS article.

Exhaust System Backpressure

Before replacing any components, check exhaust system for restrictions. Use a vacuum gauge or a low-pressure (0-5 psi) gauge to check exhaust system.

If a vacuum gauge is used, connect vacuum gauge hose to intake manifold vacuum port and start engine. Observe vacuum gauge. Partially open throttle and hold steady. If vacuum gauge reading slowly drops after stabilizing, exhaust system should be checked for a restriction. If using a low pressure gauge, connect gauge in the following manner

1. Check At Oxygen Sensor Remove oxygen sensor. Install backpressure tester in place of oxygen sensor. After test is completed, coat oxygen sensor threads with anti-seize compound before installation.

DEFINITION

No-start is defined as engine cranks okay but does not start. Engine may fire a few times.

NO START - ENGINE CRANKS OKAY

Note. Before performing following tests, check battery condition, engine cranking speed and fuel supply.

Ignition System

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. Install Tech 1 scan tool. Using scan tool, monitor Throttle Position (TP) sensor. Ensure is throttle closed. If TP sensor value is greater than 2.5 volts, diagnose using DTC P0123. See the TESTS W/CODES article. If TP sensor voltage is less than 2.5 volts, go to next step.
3. Using scan tool, monitor Engine Coolant Temperature (ECT) sensor. If ECT sensor value is less than -30°C, diagnose using DTC P0118. See the TESTS W/CODES article. If ECT sensor is greater than -30°C, go to next step.
4. Turn ignition off for 10 seconds. Turn ignition on. Fuel pump should operate for about 2 seconds. If fuel pump operates as specified, go to next step. If fuel pump does not operate as specified, go to FUEL SYSTEM.
5. Turn ignition off. Disconnect injector harness connector at intake manifold. Using a test light connected to ground, probe injector feed circuit. See the WIRING DIAGRAMS article. Turn ignition on with engine off. If test light flashes, go to next step. If test light does not flash, go to step 8).
6. Disconnect one spark plug wire. Install Spark Tester (J-26792). Crank engine. If spark is present, go to next step. If spark is not present, diagnose enhanced ignition system.
7. Reconnect spark plug wire. Turn ignition off. Connect fuel pressure gauge. Turn ignition on with engine off. Observe fuel pressure. Fuel pressure should be 55-61 psi (3.9-4.3 kg/cm 2 ). If fuel pressure is as specified, perform fuel injector balance test. See INJECTOR BALANCE TEST under FUEL SYSTEM in the SYSTEM/COMPONENT TESTS article. If fuel pressure is not as specified, diagnose fuel system. See «BASIC FUEL SYSTEM CHECKS»(ref-20660-S23841452632001010200000) .
8. Repair injector ignition feed circuit. After repairs, go to next step.
9. 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, go to step 2).
10. Warm engine to normal operating temperature. Using scan tool, select DTC, FAILED THIS IGN function. If DTC(s) are displayed, diagnose DTC(s). See the TESTS W/CODES article. If DTC(s) are not present, go to next step.
11. Select CAPTURE INFO, REVIEW INFO function. If additional DTC(s) are displayed, diagnose DTC(s). See the TESTS W/CODES article. If DTC(s) are not present, system is okay.

Fuel System

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. Turn ignition off for about 10 seconds. Turn ignition on. Fuel pump should operate for about 2 seconds. If fuel pump operates as specified, go to IGNITION SYSTEM check. If fuel pump does not operate as specified, go to next step.
3. Connect a fused jumper wire between battery positive and fuel pump test terminal. If fuel pump operates, go to next step. If fuel pump does not operate, go to step 12).
4. Disconnect jumper wire from test terminal. Turn ignition off for 10 seconds. Turn ignition on. Fuel pump should operate for about 2 seconds. If fuel pump operates as specified, go to step 25). If fuel pump does not operate as specified, go to next step.
5. Remove fuel pump relay. Turn ignition on with engine off. Using a test light connected to ground, probe fuel pump relay harness connector battery feed terminal (Orange wire). If test light illuminates, go to next step. If test light does not illuminate, go to step 14).
6. Connect test light between ground and fuel pump relay harness connector 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 15).
7. Connect test light between ground and fuel pump relay terminal. Turn ignition off for 10 seconds. Turn ignition on. If test light illuminates for 2 seconds, then turns off, go to next step. If test light does not illuminate, go to step 16).
8. Check for faulty fuel pump relay harness connector. Repair as necessary. After repairs, go to step 11). If connector is okay, go to next step.
9. Replace fuel pump relay. After repairs, go to next step.
10. Start and warm engine to normal operating temperature. Ensure oil pressure is within normal range. Disconnect fuel pump relay. If engine continues to run, go to next step. If engine stalls/dies, go to step 17).
11. Reinstall fuel pump relay. Turn ignition off. Using a test light connected to ground, probe fuel pump test connector. If test light illuminates, go to step 18). If test light does not illuminate, go to step 25).
12. Disconnect fuel pump harness connector. Using a fused jumper wire connected to battery voltage, jumper fuel pump test terminal. Using a test light connected to ground, probe fuel pump feed circuit. See the WIRING DIAGRAMS article. If test light illuminates, go to next step. If test light does not illuminate, go to step 20).
13. Connect test light to fuel pump ground terminal on harness connector. If test light illuminates, go to step 19). If test light does not illuminate, go to step 21).
14. Repair open in battery feed circuit to fuel pump relay harness connector terminal. After repairs, go to step 25).
15. Repair open in fuel pump relay ground circuit. After repairs, go to step 25).
16. Check for faulty connection at VCM connector fuel pump relay control circuit. Check for open or short to ground in harness between fuel pump relay control connector terminal and fuel pump relay control circuit. Repair as necessary. After repairs, go to step 22). If circuits are okay, go to step 24).
17. Check for faulty oil pressure switch connector terminals. Repair as necessary. After repairs, go to step 22). If connector terminals are okay, go to next step.
18. Replace oil pressure switch. After repairs, go to step 25).
19. Replace fuel pump. After repairs, go to step 25).
20. Repair open between fuel pump test terminal and fuel pump feed circuit at fuel pump harness connector. After repairs, go to step 25).
21. Repair open in fuel pump harness ground circuit. After repairs, go to step 25).
22. Repair affected circuit as necessary. After repairs, go to step 25).
23. Repair connectors as necessary. After repairs, go to step 25).
24. Replace VCM. Perform VCM relearn procedures. After repairs, go to next step.
25. Clear DTC(s) using scan tool. 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).
26. 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.
27. Select CAPTURE INFO, REVIEW INFO function. If additional DTC(s) are displayed, diagnose DTC(s). See the TESTS W/CODES article. If DTC(s) are not present, system is okay.

FUEL SYSTEM PRESSURE RELIEF

Fuel system is under pressure, which must be relieved before servicing fuel system. Fuel pressure may be relieved by the following method

1. Disconnect negative battery cable. Loosen fuel filler cap. Install Fuel Pressure Gauge (J-34730-1A) to fuel pressure test head. Wrap shop towel around pressure connection when installing fuel pressure gauge to absorb fuel leakage. Place gauge bleed hose in container. Open bleed valve to relieve fuel pressure.

BASIC IGNITION SYSTEM CHECKS

Note. To diagnose ignition system, see appropriate IGNITION SYSTEM test in NO-START DIAGNOSIS .

IDLE SPEED & IGNITION TIMING

Ensure idle speed and ignition timing are set to specifications. For specifications, see SPECIFICATIONS article. For adjustment procedures, see ADJUSTMENTS article.

MALFUNCTION INDICATOR LIGHT (MIL)

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. Turn engine off for 15 seconds. Turn ignition on with engine off. If Malfunction Indicator Light (MIL) illuminates, go to step 4). If MIL does not illuminate, go to next step.
3. Start engine. If engine starts, go to step 6). If engine does not start, go to step 7).
4. Install Tech 1 scan tool. Turn ignition on. Using scan tool, command MIL to turn on and off. If MIL turns on and off as commanded, go to step 25). If MIL does not turn on and off as commanded, go to next step.
5. Turn ignition off. Disconnect VCM harness connectors. Turn ignition on. If Malfunction Indicator Light (MIL) illuminates, go to step 19). If MIL does not illuminate, go to step 11).
6. Turn ignition off. Disconnect VCM harness connectors. Turn ignition on. Using a fused jumper connected to ground, probe VCM harness connector MIL control circuit. See the WIRING DIAGRAMS article. If MIL illuminates, go to step 11). If MIL does not illuminate, go to step 8).
7. Check for open in ignition and battery fuses. If fuses are okay, go to step 9). If fuse(s) is open, go to step 10).
8. Check for open in fused jumper. If fused jumper is okay, go to step 13). If fused jumper is open, go to step 14).
9. Turn ignition off. Disconnect VCM harness connectors. Turn ignition on. Using a test light connected to ground, probe VCM harness connector ignition feed circuit. See the WIRING DIAGRAMS article. If test light illuminates, go to step 18). If test light does not illuminate, go to step 20).
10. Check for short to ground in fuse circuit that was open. Repair as necessary and replace fuse. After repairs, go to step 25).
11. Check for faulty VCM connections. If connections faulty okay, go to step 23). If connections are okay, go to step 24).
12. Repair open in ignition feed circuit. After repairs, go to step 25).
13. Repair short to voltage in MIL control circuit. After repairs, go to step 25).
14. Check for open in MIL control circuit. See the WIRING DIAGRAMS article. Repair as necessary. After repairs, go to step 23). If circuit is okay, go to next step.
15. Check for open in ignition feed circuit or fuse to MIL. See the WIRING DIAGRAMS article. Repair as necessary. After repairs, go to step 23). If circuit or fuse is okay, go to next step.
16. Check for an open MIL bulb. If light bulb is faulty, go to step 23). If light bulb is okay, go to next step.
17. Replace instrument panel assembly. After replacing instrument panel, go to step 25).
18. Turn ignition off. Disconnect VCM harness connectors. Turn ignition on. Using test light connected to ground, probe VCM harness connector battery feed circuit. See the WIRING DIAGRAMS article. If test light illuminates, go to step 21). If test light does not illuminate, go to step 22).
19. Repair short to ground in MIL control circuit. After repairs, go to step 25).
20. Repair open in ignition feed circuit. After repairs, go to step 25).
21. Check for faulty VCM ground connection at engine block. Repair as necessary. After repairs, go to step 23). If connections were okay, go to step 11).
22. Repair open in battery feed circuit. After repairs, go to step 25).
23. Repair as necessary. After repairs, go to step 25).
24. Replace VCM. Perform VCM relearn procedures. After repairs, go to next step.
25. Warm engine to normal operating temperature. Check if any DTC(s) are set. Diagnose any DTC present. See the TESTS W/CODES article. If DTC(s) are not present, system is okay.

SUMMARY

If no faults were found while performing BASIC DIAGNOSTIC PROCEDURES, no trouble codes (or only intermittent ones) were found while performing ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK and driveability problems exist, proceed to the TESTS W/O CODES article for diagnosis by symptom (i.e., ROUGH IDLE, NO-START, etc.) or intermittent diagnostic procedures.