Engine Controls - Basic Diagnostic Procedures - 6.5L Diesel: 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.

Basic System Check

1. Perform On-Board Diagnostic (OBD) System Check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-20661-S20543652542001010200000) . After performing OBD system check, go to next step.
2. Check battery condition. If battery is okay, go to next step. If battery condition is not okay, go to step 23).
3. Check fuel level in tank. If fuel level is okay, go to next step. If fuel level is not okay, go to step 23).
4. Check quality of fuel. If fuel quality is okay, go to next step. If fuel quality is not okay, go to step 23).
5. Check glow plug operation. If glow plug operation is okay, go to next step. If glow plug operation is not okay, go to step 23).
6. Check for proper cranking speed. If cranking speed is okay, go to next step. If cranking speed is not okay, go to step 23).
7. Check for restriction in fuel return system. If restriction is not present, go to next step. If return line is restricted, go to step 23).
8. Check injection pump ground wire. If ground is okay, go to next step. If ground is not okay, go to step 23).
9. Turn ignition on. Observe Malfunction Indicator Light (MIL). If MIL illuminates, go to step 10). If MIL does not illuminate, go to «MALFUNCTION INDICATOR LIGHT (MIL)»(ref-20661-S33647617322001010200000) .
10. Install Tech 1 scan tool. Using scan tool, check for any data display. If data is displayed, go to next step. If data is not displayed, go to «DLC DIAGNOSIS OR NO SCAN TOOL DATA»(ref-20661-S14314525672001010200000) .
11. Loosen injector line at injector. Crank engine. If fuel comes out of fuel line, go to step 17). If fuel is not coming out of fuel line, go to next step.
12. Disconnect optical/fuel temperature sensor. Attempt to start engine. If engine does not start, go to next step. If engine starts, go to step 16).
13. Reconnect optical/fuel temperature sensor. Disconnect fuel solenoid driver. While cranking engine, check voltage between ground and fuel injector control circuit at harness terminal. See the WIRING DIAGRAMS article. Voltage should be 1.2 volts or greater. If voltage is as specified, go to next step. If voltage is not as specified, go to step 18).
14. With fuel solenoid driver still disconnected, probe solenoid ground circuit with test light connected to battery voltage at harness connector. See the WIRING DIAGRAMS article. If test light illuminates, go to next step. If test light does not illuminate, go to step 19).
15. Turn ignition on with engine off. Using test light connected to ground, probe ignition feed circuit at fuel solenoid harness connector. See the WIRING DIAGRAMS article. If test light illuminates, go to next step. If test light does not illuminate, go to step 21).
16. Replace fuel injection pump. After repairs, go to step 25).
17. Injection system is okay. See the TESTS W/O CODES article.
18. Check for open or short in circuit between fuel solenoid driver and PCM. Repair as necessary. After repairs, go to step 22). If circuit is okay, go to step 20).
19. Check closure signal ground circuit for open between fuel solenoid driver and PCM. Repair as necessary. After repairs, go to step 22). If circuit is okay, go to next step.
20. Check for faulty solenoid driver and PCM connectors. Repair as necessary. After repairs, go to step 22). If connectors are okay, go to step 24).
21. Repair open in ignition feed circuit (Pink wire). After repairs, go to step 25).
22. Repair circuit as necessary. After repairs, go to step 25).
23. Repair as necessary. After repairs, go to step 25).
24. Replace PCM. Perform PCM relearn procedures. After repairs, go to next step.
25. 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).
26. Warm engine to normal operating temperature. Using scan tool, select DTC, FAILED THIS IGN function. If any DTC(s) are present, go to next step.
27. Select CAPTURE INFO, REVIEW INFO function. If any other DTC(s) are displayed that have not been diagnosed, see the TESTS W/CODES article. If DTC(s) are not present, system is okay.

MALFUNCTION INDICATOR LIGHT (MIL)

1. Perform On-Board Diagnostic (OBD) System Check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-20661-S20543652542001010200000) . After performing OBD system check, go to next step.
2. Attempt to start engine. If engine starts, go to next step. If engine does not start, go to step 6).
3. Check fuse No. 4 (Gauges). If fuse if faulty, go to step 14). If fuse is okay, go to next step.
4. Turn ignition on. Using a test light connected to ground, probe ignition feed terminal at instrument cluster connector. See the WIRING DIAGRAMS article. If test light illuminates, go to step 5). If test light does not illuminate, go to step 11).
5. Turn ignition off. Disconnect Blue PCM harness connector. Turn ignition on. Using a fused jumper wire connected to ground, jumper MIL control circuit at PCM connector terminal. See the WIRING DIAGRAMS article. If MIL illuminates, go to step 9). If test light does not illuminate, go to step 10).
6. Check fuses to PCM ignition and battery feed circuit. If fuses are okay, go to next step. If fuse(s) are faulty, go to step 13).
7. Turn ignition off. Disconnect PCM connectors. Turn ignition on. Using a test light connected to ground, probe PCM harness connector ignition and battery feed circuits. 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).
8. Check for faulty or poor PCM ground connections. Repair as necessary. After repairs, go to step 20). If ground connections are okay, go to next step.
9. Check for poor connection at PCM harness connector. Repair as necessary. After repairs, go to step 20). If connector is okay, go to step 15).
10. Check for open in MIL control circuit. Repair as necessary. After repairs, go to step 20). If circuit is okay, go to step 16).
11. Repair open in ignition feed circuit to instrument cluster. After repairs, go to step 20).
12. Locate and repair open in PCM battery feed or ignition circuit. Repair as necessary. After repairs, go to step 20).
13. Locate and repair short to ground in PCM ignition feed circuit or PCM battery feed circuit. Repair as necessary. After repairs, go to step 20).
14. Locate and repair short to ground in instrument cluster ignition feed circuit. After repairs, go to step 20).
15. Replace PCM. Perform PCM relearn procedures. After repairs, go to step 20).
16. Check for poor connection at MIL control circuit to instrument cluster connector. Repair as necessary. After repairs, go to step 20). If circuit is okay, go to next step.
17. Remove instrument cluster assembly. Inspect MIL bulb. If bulb is okay, go to step 19). If bulb is faulty, go to next step.
18. Replace MIL bulb. After replacing bulb, go to step 20).
19. Replace instrument cluster. After repairs, go to step 20).
20. 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).
21. Warm engine to normal operating temperature. Using scan tool, select DTC, FAILED THIS IGN function. Diagnose any DTC present. See the TESTS W/CODES article. If DTC(s) are not present, go to next step.
22. Select CAPTURE INFO, REVIEW INFO function. If DTC(s) are present. 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.