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Engine Controls - Basic Diagnostic Procedures - 6.5L Diesel: Diagnosis Chevrolet Tahoe I

Testing & Diagnostics ~2164 words

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

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. In very cold temperatures, ensure oil is proper viscosity and not contaminated.

Fuel Pump Test

  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. Turn ignition off for about 10 seconds. Turn ignition on. Fuel pump should operate during glow plug cycle. If fuel pump operates, go to BASIC SYSTEM CHECK. If fuel pump does not operate, 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 during glow plug cycle. If fuel pump operates, go to step 25). If fuel pump does not operate, 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 20 seconds. Turn ignition on. Test light should illuminate during glow plug cycle, then turn off. If test light illuminates as specified, go to next step. If test light does not illuminate as specified, 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 step 25). If fuel pump relay is okay, 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 PCM 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 PCM. Perform PCM 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 - 6.5L article. If DTC(s) are not present, system is okay.

FUEL PUMP FLOW TEST

  1. Disconnect fuel line at fuel filter inlet. Disconnect fuel injection pump electric shut-off solenoid wire. See the WIRING DIAGRAMS article.
  2. Crank engine for 15 seconds. If fuel pump does not supply about1/2 pint of fuel in 15 seconds, go to FUEL SYSTEM PRESSURE TEST.

FUEL SYSTEM PRESSURE TEST

Note. For fuel pump circuit testing, see appropriate FUEL SYSTEM test in NO-START DIAGNOSIS .

  1. Turn engine off. Disconnect fuel line at inlet to fuel filter assembly. Install low pressure fuel gauge to fuel line.
  2. Crank or run engine 10-15 seconds. If fuel pressure is not 4 psi (.28 kg/cm 2 ), check fuel lines and fuel tank sending unit for restriction. If fuel lines and sending unit are okay, replace fuel pump.

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 and BASIC FUEL 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)»(ref-20661-S33647617322001010200000) . If MIL illuminates, go to next step. If MIL does not illuminate, go to «MALFUNCTION INDICATOR LIGHT (MIL)»(ref-20661-S33647617322001010200000) .
  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 PCM data, go to next step. If scan tool does not display PCM data, go to «DLC DIAGNOSIS OR NO SCAN TOOL DATA»(ref-20661-S14314525672001010200000) .
  3. Using scan tool, command MIL to turn off. If MIL turns off, go to next step. If MIL does not turn off, diagnose using DTC P1641. See the TESTS W/CODES article.
  4. Using scan tool, check if any DTC(s) are present. If DTC(s) are present, go to next step. If DTC(s) are not present, go to step 6).
  5. Using scan tool, store FREEZE FRAME and FAILURE RECORDS data. Diagnose any stored DTC using the TESTS W/CODES article.
  6. Start engine. If engine starts and runs, go to next step. If engine does not start, or starts and stalls/dies, go to «NO-START DIAGNOSIS»(ref-20661-S32958043912001010200000) .
  7. Turn ignition on with engine off. Check Engine Coolant Temperature (ECT). Start and warm engine to 194-203°F (90-95°C). Using scan tool, read ECT sensor value while engine reaches specified temperature. Compare scan tool value with actual control system values. If value is within limits, go to the TESTS W/O CODES article. If value is not within limits, diagnose DTC(s) using the TESTS W/CODES article.

DLC DIAGNOSIS OR NO SCAN TOOL DATA

  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. Turn ignition off for 30 seconds. Turn ignition on with engine off. Observe MIL. If MIL illuminates, go to next step. If MIL does not illuminate, go to «MALFUNCTION INDICATOR LIGHT (MIL)»(ref-20661-S33647617322001010200000) .
  3. Install scan tool. If scan tool communicates with PCM, go to next step. If scan tool does not communicate with PCM, 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, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-20661-S20543652542001010200000) . If MIL does not turn on and off as commanded, go to next step.
  5. Turn ignition off. Disconnect PCM harness connectors. Turn ignition on. If Malfunction Indicator Light (MIL) illuminates, go to step 17). If MIL does not illuminate, go to next step.
  6. Using scan tool, check engine calibration ID. If proper ID is displayed, go to step 26). If proper ID not displayed, go to step 18).
  7. Connect a test light to ground. Using test light, probe DLC terminal No. 16. See the WIRING DIAGRAMS article. If test light illuminates, go to next step. If test light does not illuminate, go to step 19).
  8. Connect a test light to battery voltage. Using test light, probe DLC terminals No. 4 and 5. See the WIRING DIAGRAMS article. If test light illuminates on both circuits, go to next step. If test light does not illuminate on either circuit, go to step 20).
  9. 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 21).
  10. Install and check scan tool on another vehicle. If scan tool works, go to next step. If scan tool does not work, go to step 22).
  11. Disconnect scan tool. Using DVOM, check voltage between ground and PCM serial data line at DLC terminal No. 2. See the WIRING DIAGRAMS article. If voltage is less than 7 volts, go to next step. If voltage is 7 volts or greater, go to step 15).
  12. Using DVOM, again check voltage between ground and DLC terminal No. 2. If voltage is less than one volt, go to next step. If voltage is one volt or greater, go to step 16).
  13. Turn ignition off. Using DVOM, check resistance between ground and DLC terminal No. 2. If resistance is less than 10 ohms, go to next step. If resistance is 10 ohms or greater, go to step 25).
  14. Disconnect PCM connectors. Using DVOM, check resistance between ground and DLC terminal No. 2. If resistance is less than 10 ohms, go to step 23). If resistance is 10 ohms or greater, go to step 26).
  15. Turn ignition off. Disconnect PCM connectors. Turn ignition on. Check voltage on DLC terminal No. 2. Voltage should not be present. If voltage is not as specified, go to step 24). If voltage is as specified, go to step 26).
  16. Reprogram EEPROM and retest. If serial data is present, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-20661-S20543652542001010200000) . If serial data is not present, go to step 26).
  17. Repair short to ground in MIL control circuit. After repairs, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-20661-S20543652542001010200000) .
  18. Reprogram EEPROM and retest. After repairs, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-20661-S20543652542001010200000) .
  19. Check fuse No. 7 (PWR AUX). If fuse is faulty, repair short to ground in DLC terminal No. 16 circuit. If fuse is okay, repair open in DLC terminal No. 16 circuit. After repairs, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-20661-S20543652542001010200000) .
  20. Repair open in affected circuit. After repairs, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-20661-S20543652542001010200000) .
  21. Repair cigarette lighter circuit. After repairs, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-20661-S20543652542001010200000) .
  22. Repair or replace faulty scan tool and/or cables. After repairs, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-20661-S20543652542001010200000) .
  23. Repair short to ground in serial data line. After repairs, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-20661-S20543652542001010200000) .
  24. Repair short to voltage in serial data line. After repairs, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-20661-S20543652542001010200000) .
  25. Check for open in serial data line. If circuit is okay, check PCM and DLC connectors. If connectors are okay, replace PCM. Perform PCM relearn procedures. After repairs, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-20661-S20543652542001010200000) .
  26. Replace PCM. Reprogram replacement PCM. After replacing PCM, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-20661-S20543652542001010200000) .

More articles — Engine Controls - Basic Diagnostic Procedures - 6.5L Diesel