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Engine Controls - Trouble Shooting - No Codes GMC Yukon Denali GMT800

Testing & Diagnostics ~7712 words

INTRODUCTION

Note. Models may use an Engine Control Module (ECM), Powertrain Control Module (PCM) or Vehicle Control Module (VCM). The term PCM will be used in this article to describe all control modules.

Before diagnosing symptoms or intermittent faults, perform steps in appropriate BASIC DIAGNOSTIC PROCEDURES or SELF-DIAGNOSTICS articles. Use this article to diagnose driveability problems if a current DTC is not present.

Symptom checks are intended to direct technician to malfunctioning component(s) for further diagnosis. A symptom should lead to a specific component or system test, or an adjustment specification. Use intermittent test procedures to locate driveability problems not occurring when vehicle is being tested.

Note. For specific testing procedures, see appropriate SYSTEM & COMPONENT TESTING article. For specifications, see appropriate SERVICE & ADJUSTMENT SPECIFICATIONS article.

Note. SERVICE ENGINE SOON light, located on instrument cluster, is also referred to as Malfunction Indicator Light (MIL).

PRELIMINARY INSPECTION

  1. Verify on-board diagnostics are working by performing DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS in appropriate SELF-DIAGNOSTICS article.
  2. Ensure PCM and MIL functions properly.
  3. Ensure no DTCs (except intermittent) are stored.
  4. Ensure fuel control system operates properly. See appropriate BASIC DIAGNOSTIC PROCEDURES article.
  5. Perform fuel system pressure test.
  6. Visually inspect all systems.

After all checks have been performed, verify customer complaint and locate correct symptom. Check items indicated under that symptom. Not all items listed under each symptom apply to all models and systems. These procedures normally recommend testing of a specific system or component, such as EGR, TCC, etc. See appropriate SYSTEM & COMPONENT TESTING article for test procedures.

SYMPTOMS (GASOLINE)

Note. Before proceeding with any symptom diagnosis, perform all steps under PRELIMINARY INSPECTION .

Note. If PCM displays data but engine fails to start, see NO-START DIAGNOSIS in appropriate BASIC DIAGNOSTIC PROCEDURES article.

SYMPTOM DIAGNOSIS

Symptom checks should not be used unless symptom occurs while vehicle is being tested. To reduce diagnostic time, ensure steps in appropriate BASIC DIAGNOSTIC PROCEDURES and SELF-DIAGNOSTICS articles were performed before diagnosing a symptom. Symptoms available for diagnosis include

  1. «Detonation/Spark Knock»(/gmc/yukon-denali/gmt800-1999-2006/remont/testing-diagnostics/#engine-controls-trouble-shooting-no-codes)
  2. «Engine Backfires»(/gmc/yukon-denali/gmt800-1999-2006/remont/testing-diagnostics/#engine-controls-trouble-shooting-no-codes)
  3. «Engine Cuts Out, Misses»(/gmc/yukon-denali/gmt800-1999-2006/remont/testing-diagnostics/#engine-controls-trouble-shooting-no-codes)
  4. «Engine Dieseling/Run-On»(/gmc/yukon-denali/gmt800-1999-2006/remont/testing-diagnostics/#engine-controls-trouble-shooting-no-codes)
  5. «Hard Start»(/gmc/yukon-denali/gmt800-1999-2006/remont/testing-diagnostics/#engine-controls-trouble-shooting-no-codes)
  6. «Hesitation, Sag Or Stumble»(/gmc/yukon-denali/gmt800-1999-2006/remont/testing-diagnostics/#engine-controls-trouble-shooting-no-codes)
  7. «Lack Of Power Or Sluggish»(/gmc/yukon-denali/gmt800-1999-2006/remont/testing-diagnostics/#engine-controls-trouble-shooting-no-codes)
  8. «Poor Fuel Economy»(/gmc/yukon-denali/gmt800-1999-2006/remont/testing-diagnostics/#engine-controls-trouble-shooting-no-codes)
  9. «Poor Fuel Fill Quality»(/gmc/yukon-denali/gmt800-1999-2006/remont/testing-diagnostics/#engine-controls-trouble-shooting-no-codes)
  10. «Rough, Unstable Or Incorrect Idle and Stalling»(/gmc/yukon-denali/gmt800-1999-2006/remont/testing-diagnostics/#engine-controls-trouble-shooting-no-codes)
  11. «Vehicle Surges Or Chuggles»(/gmc/yukon-denali/gmt800-1999-2006/remont/testing-diagnostics/#engine-controls-trouble-shooting-no-codes)

Symptom Definition

A mild to severe ping, usually worse during acceleration. Engine makes sharp metallic knocks which change with degree of acceleration.

Possible Causes & Corrections

Check the following items

  1. Check coolant level. Check cooling system thermostat for proper operation and application.
  2. Check cooling fan for proper operation.
  3. Check for restricted airflow to radiator or restricted coolant flow through radiator.
  4. Check for loose water pump belt.
  5. Check Knock Sensor (KS) system for no retard.
  6. Remove spark plugs and check for correct heat range, wear, cracks, wetness, improper gap or heavy deposits.
  7. Check for incorrect mechanical engine parts such as camshaft, cylinder heads and pistons.
  8. Check transmission shift pattern and downshift operation.
  9. Check Transaxle Range (TR) switch input with vehicle in Drive and shifter in Drive or Overdrive.
  10. Check Torque Converter Clutch (TCC) for proper operation.
  11. Check Park Neutral Position (PNP) switch circuit. Ensure PNP switch is properly adjusted.
  12. Ensure initial timing is correct.
  13. Check PCM grounds. Ensure they are clean, tight and properly located.
  14. Inspect the items that can cause an engine to run lean long term fuel trim near 24 percent.
  15. Remove carbon from engine with top engine cleaner.
  16. Check fuel system for incorrect fuel pressure. Perform BASIC FUEL SYSTEM CHECKS. See FUEL SYSTEMS in appropriate BASIC DIAGNOSTIC PROCEDURES article.
  17. Check for poor fuel quality and proper octane rating. If scan tool readings are normal and no engine mechanical faults are present, fill fuel tank with a premium fuel and re-evaluate vehicle performance.
  18. Check for a shifted Engine Coolant Temperature (ECT) sensor. See DIAGNOSTIC TESTS in appropriate SELF-DIAGNOSTICS article.
  19. If emission test shows excessive NOx emissions, check all systems and components which could cause engine to run lean or too hot.
  20. Check EGR operation.
  21. Ensure correct PCM program is installed in vehicle. Check dealer for latest application.

Fuel ignites within intake manifold or in exhaust system, making a loud popping noise.

Check the following items

  1. Check for engine vacuum leaks. Ensure engine is tuned to specifications.
  2. Inspect the Secondary Air Injection (AIR) system.
  3. Using Spark Tester (J-26792), check available output voltage of ignition coil.
  4. Check air induction system for restrictions or air leaks.
  5. Check exhaust system for restrictions, such as a damaged or collapsed pipe, muffler or catalytic converter. See EXHAUST SYSTEM BACKPRESSURE under MECHANICAL INSPECTION in appropriate BASIC DIAGNOSTIC PROCEDURES article.
  6. Check fuel injectors. Perform injector balance test. See FUEL INJECTOR BALANCE TEST under FUEL SYSTEMS in appropriate SYSTEM & COMPONENT TESTING article.
  7. Check fuel system for incorrect fuel pressure. See BASIC FUEL SYSTEM CHECKS in appropriate BASIC DIAGNOSTIC PROCEDURES article.
  8. Inspect that each injector harness is connected to the correct injector or cylinder according to the firing order.
  9. Check engine compression. Check for incorrect valve timing, bent push rods, broken valve springs or worn camshaft lobes.
  10. Check transmission shift solenoid system and Torque Converter Clutch (TCC) system for proper operation.
  11. Check for intermittent ignition system problem.
  12. Check intake and exhaust manifold passages for casting flash.
  13. Remove spark plugs and check for wet plugs, cracks, improper gap, burned electrodes or heavy carbon deposits. Also, check condition of spark plug wires. Spray spark plug wires with a fine mist of water to check for shorts.
  14. Ensure initial ignition timing is properly set.
  15. Ensure speedometer is properly calibrated.

Cuts out, misses is defined as a steady pulsation or jerking following engine speed, usually more pronounced as engine load increases. Exhaust may have a steady spitting sound at idle or low speed. Perform visual inspection as described in appropriate BASIC DIAGNOSTIC PROCEDURES article.

Check the following items

  1. Check for restricted exhaust system. See EXHAUST SYSTEM BACKPRESSURE under MECHANICAL INSPECTION in appropriate BASIC DIAGNOSTIC PROCEDURES article.
  2. Monitor the Misfire Current Counters while driving the vehicle in the conditions that the misfire occurred. If a cylinder can be located with a misfire, see appropriate SELF-DIAGNOSTICS article.
  3. Check engine compression. Check for incorrect valve timing, bent push rods, broken valve springs or worn camshaft lobes.
  4. Using Spark Tester (J-26792), check for adequate spark at spark plugs.
  5. Check ignition system for faulty ground and power feed circuits.
  6. Check for proper Crankshaft Position (CKP) and Camshaft Position (CMP) sensor resistance.
  7. Remove spark plugs and check for wet plugs, cracks, improper gap, burned electrodes or heavy carbon deposits. Also, check condition of spark plug wires. Spray spark plug wires with a fine mist of water to check for shorts.
  8. Check Transaxle Range (TR) switch input with vehicle in drive and shifter in drive or overdrive.
  9. Check for poor quality or alcohol contaminated fuel.
  10. Check fuel injectors. Perform injector balance test. See FUEL INJECTOR BALANCE TEST under FUEL SYSTEMS in appropriate SYSTEM & COMPONENT TESTING article.
  11. Check fuel system for incorrect fuel pressure. See BASIC FUEL SYSTEM CHECKS in appropriate BASIC DIAGNOSTIC PROCEDURES article.
  12. Inspect items that cause an engine to run rich, long term fuel trim near -13 percent.
  13. Inspect items that can cause an engine to run lean, long term fuel trim near 24 percent.
  14. Check PCM grounds. Ensure they are clean, tight and properly located.
  15. Check TP sensor for sticking and binding. Check for correct TP sensor voltage. See FUEL SYSTEMS in appropriate SERVICE & ADJUSTMENT SPECIFICATIONS article.
  16. Use a scan tool in order to monitor the Knock Sensor (KS) system for excessive spark retard activity.

Engine continues to run (but very rough) after ignition is turned off. If engine runs smoothly, check ignition switch.

Check for the following

  1. Check PCM grounds. Ensure they are clean, tight and properly located.
  2. Check for poor quality or alcohol contaminated fuel.
  3. Check canister purge system (staying on).
  4. Check for fuel in pressure regulator vacuum hose. If fuel is present, replace regulator.
  5. Check fuel system for incorrect fuel pressure. See BASIC FUEL SYSTEM CHECKS in appropriate BASIC DIAGNOSTIC PROCEDURES article.
  6. Check fuel injectors. Perform injector balance test. See FUEL INJECTOR BALANCE TEST under FUEL SYSTEMS in appropriate SYSTEM & COMPONENT TESTING article.
  7. Check injector harness locations. Ensure injectors are connected to correct injector/cylinder according to firing order.

Engine cranks okay, but does not start immediately. Engine eventually starts and may run okay or soon stall.

Check the following items

  1. Check exhaust system for restrictions, such as a damaged or collapsed pipe, muffler or catalytic converter. See EXHAUST SYSTEM BACKPRESSURE under MECHANICAL INSPECTION in appropriate BASIC DIAGNOSTIC PROCEDURES article.
  2. Check ignition system for bare or shorted spark plug wires, loose ignition coil connections. Check for shorts by misting plug wires with water.
  3. Check ignition system for faulty grounds.
  4. Using Spark Tester (J-26792), check for adequate spark output.
  5. Remove spark plugs. Check for wet/fouled spark plugs, cracks in porcelain, improper gap, burned electrodes or heavy carbon deposits.
  6. Check fuel pump relay. Connect test light between fuel pump test terminal and ground. Turn ignition on. Test light should illuminate for 2 seconds. If test light does not illuminate, check fuel pump relay. For location of fuel pump relay and test connector, see appropriate SYSTEM & COMPONENT TESTING article.
  7. Check for poor fuel quality or alcohol/water-contaminated fuel.
  8. Inspect both injector fuses for being open. An open injector fuse causes four injectors and four ignition coils not to operate. Replace the fuse. Inspect the injector circuits and the ignition coil circuits for an intermittent short to ground.
  9. Check fuel system for incorrect fuel pressure. See BASIC FUEL SYSTEM CHECKS in appropriate BASIC DIAGNOSTIC PROCEDURES article.
  10. Check for plugged injectors. Perform injector balance test. See FUEL INJECTOR BALANCE TEST under FUEL SYSTEMS in appropriate SYSTEM & COMPONENT TESTING article.
  11. Check for faulty in-tank fuel pump check valve (if equipped). A faulty check valve allows fuel in lines to drain back to tank after engine is stopped.
  12. Check EGR operation.
  13. Ensure Engine Coolant Temperature (ECT) sensor circuit resistance is not too high. See appropriate SENSOR OPERATING RANGE CHARTS article.
  14. Ensure TP sensor does not stick or bind. A sticking throttle shaft or binding linkage may cause a high TP sensor voltage (open throttle indication). PCM will not control idle if high voltage is sensed.
  15. Check Idle Air Control (IAC) system. Check for vacuum leak at high idle. Check for binding of throttle blade or linkage. Check for foreign material in IAC bore of throttle body. Check for proper connection of IAC valve electrical connector.
  16. Check resistance of ECT and Intake Air Temperature (IAT) sensors. On a cold engine, ECT and IAT sensor readings should be within 5°F of each other.
  17. Ensure correct PCM program is installed in vehicle. Check with dealer for latest application information.
  18. Inspect the Mass Air Flow (MAF) sensor installation. A MAF sensor that is incorrectly installed may cause a hard start. The embossed arrows on the MAF sensor indicate the direction of the intake air flow. The arrows must point toward the engine. Install the MAF in the proper direction.
  19. Inspect Crankshaft Position (CKP) sensor clearance and resistance Check harmonic balancer interrupter rings for bent or missing vanes.
  20. Inspect the Camshaft Position (CMP) sensor for proper mounting and/or a bad connection. A long crank time occurs if the PCM does not receive a CMP signal.
  21. Check PCM and engine grounds for correct locations, tight and clean connections. See WIRING DIAGRAMS article.

Momentary lack of response when accelerator is pushed down. May occur at any vehicle speed. Usually occurs after a stop. If severe enough, may cause engine to stall.

Check for the following items

  1. Remove spark plugs and check for wet plugs, cracks, improper gap, burned electrodes or heavy carbon deposits. Also, check condition of spark plug wires. Spray spark plug wires with a fine mist of water to check for shorts.
  2. Monitor the Misfire Current Counters while driving the vehicle in the conditions that the misfire occurred. If a cylinder can be located with a misfire, see appropriate SELF-DIAGNOSTICS article.
  3. Check for open in ignition system ground circuit. Ensure initial ignition timing is correct.
  4. Inspect the items that cause an engine to run rich long term fuel trim near -13 percent.
  5. Inspect the items that can cause an engine to run lean long term fuel trim near 24 percent.
  6. Check fuel system for incorrect fuel pressure. See BASIC FUEL SYSTEM CHECKS in appropriate BASIC DIAGNOSTIC PROCEDURES article.
  7. Check for plugged injectors. Perform injector balance test. See FUEL INJECTOR BALANCE TEST under FUEL SYSTEMS in appropriate SYSTEM & COMPONENT TESTING article.
  8. Check for poor fuel quality or water-contaminated fuel.
  9. Ensure TP sensor does not stick or bind. Voltage should increase at a steady rate as throttle is moved toward Wide Open Throttle (WOT).
  10. Check Manifold Absolute Pressure (MAP) sensor response and accuracy. See appropriate SYSTEM & COMPONENT TESTING article.
  11. Inspect the engine thermostat for proper operation and for proper heat range.
  12. Check canister purge system for proper operation.
  13. Check EGR valve for proper operation.
  14. Check exhaust system for restrictions, such as a damaged or collapsed pipe, muffler or catalytic converter. See EXHAUST SYSTEM BACKPRESSURE under MECHANICAL INSPECTION in appropriate BASIC DIAGNOSTIC PROCEDURES article.
  15. Check Heated Oxygen Sensor (HO2S) for contamination. This will cause a false high voltage signal to PCM. PCM will respond by leaning out air/fuel ratio.
  16. Ensure correct program is installed in PCM. Check dealer for latest application.
  17. Check charging system output. Repair if output is less than 9 volts or greater than 16 volts.

Engine delivers less power than expected. Little or no increase in speed when accelerator is applied.

Check the following items

  1. Check exhaust system for restrictions, such as a damaged or collapsed pipe, muffler or catalytic converter. See EXHAUST SYSTEM BACKPRESSURE under MECHANICAL INSPECTION in appropriate BASIC DIAGNOSTIC PROCEDURES article.
  2. Check engine compression. Check for incorrect valve timing, bent push rods, broken valve springs or worn camshaft lobes.
  3. Check fuel injectors. Perform injector balance test. See FUEL INJECTOR BALANCE TEST under FUEL SYSTEMS in appropriate SYSTEM & COMPONENT TESTING article.
  4. Check fuel system for incorrect fuel pressure. See BASIC FUEL SYSTEM CHECKS in appropriate BASIC DIAGNOSTIC PROCEDURES article.
  5. Check for items that cause the engine to run rich, or lean.
  6. Check transmission shift solenoid system and Torque Converter Clutch (TCC) system for proper operation.
  7. Using Spark Tester (J-26792), check for adequate spark output.
  8. Ensure correct initial ignition timing.
  9. Check Knock Sensor (KS) system for excessive retard.
  10. Check air filter and fuel filter. Replace if necessary.
  11. Check for poor fuel quality or water-contaminated fuel.
  12. Check fuel injector wires for short to ground at air cleaner.
  13. Check PCM grounds. Ensure they are clean, tight and properly located.
  14. Ensure EGR valve is not stuck open.
  15. Check for proper operation of the Transmission Fluid Pressure (TFP) manual valve switch.
  16. Check charging system output. Repair if output is less than 9 volts or greater than 16 volts.
  17. Check A/C for proper operation.
  18. Check for conditions that cause the engine torque management system to reduce engine power.

Fuel economy, as measured by an actual road test, is noticeably lower than expected. Current fuel economy is noticeably lower than previous fuel economy.

Check the following items

  1. Check for a clogged air filter.
  2. Check air induction system for restrictions or air leaks.
  3. Check exhaust system for restrictions, such as a damaged or collapsed pipe, muffler or catalytic converter. See EXHAUST SYSTEM BACKPRESSURE under MECHANICAL INSPECTION in appropriate BASIC DIAGNOSTIC PROCEDURES article.
  4. Check engine compression. Check for incorrect valve timing, bent push rods, broken valve springs or worn camshaft lobes.
  5. Check Park Neutral Position (PNP) switch circuit. Ensure PNP switch is properly adjusted.
  6. Check Torque Converter Clutch (TCC) system for proper operation.
  7. Check for dragging brakes.
  8. Check cooling system thermostat for proper heat range and operation.
  9. Ensure correct initial ignition timing.
  10. Remove spark plugs and check for wet/fouled spark plugs, cracks, improper gap, burned electrodes or heavy carbon deposits.
  11. Check fuel system for incorrect fuel pressure. See BASIC FUEL SYSTEM CHECKS in appropriate BASIC DIAGNOSTIC PROCEDURES article.
  12. Check fuel injectors. Perform injector balance test. See FUEL INJECTOR BALANCE TEST under FUEL SYSTEMS in appropriate SYSTEM & COMPONENT TESTING article.
  13. Check injector harness locations. Ensure injectors are connected to correct injector/cylinder according to firing order.
  14. Check Engine Coolant Temperature (ECT) sensor for shift in calibration. See appropriate SENSOR OPERATING RANGE CHARTS article.
  15. Check PCV system for proper operation.
  16. Check for proper Crankshaft Position (CKP) and Camshaft Position (CMP) sensor resistance.
  17. Check for fuel in pressure regulator vacuum hose. If fuel is present, replace regulator.
  18. Check for items that cause the engine to run rich.
  19. Check the Knock System (KS) for excessive spark retard.
  20. Ensure speedometer is properly calibrated.
  21. Ensure A/C system is not always on.
  22. Check for incorrect tire pressure.
  23. Check for uneven or excessive tire wear from suspension misalignment.
  24. Check with operator to see if vehicle is operated under excessive acceleration or is heavily loaded.

Problem filling fuel tank.

Possible Cause & Correction

Check the following items

  1. Fill limiter vent valve stuck closed.
  2. EVAP canister restricted.
  3. EVAP vent valve stuck closed.
  4. Restricted vapor lines.
  5. High Reid vapor pressure or high fuel temperature.
  6. Fuel filler hose is pinched or kinked.
  7. Ignition switch on (EVAP vent valve closed).

Fuel tank overfill.

Check the following items

  1. Pressure relief valve is stuck open or leaking.
  2. Fill limiter vent valve is stuck open or leaking.

Premature shut off of fuel dispensing nozzle.

Cause & Correction

Check the following items

  1. Fill limiter vent valve stuck closed.
  2. EVAP canister restricted.
  3. EVAP vent valve stuck closed.
  4. Restricted vapor lines.
  5. High Reid vapor pressure or high fuel temperature.
  6. Ignition switch on (EVAP vent valve closed).

Fuel spitback.

Check the following items

  1. EVAP canister restricted.
  2. High Reid vapor pressure or high fuel temperature.
  3. Check valve stuck closed.

Liquid to EVAP canister.

Check the following items

  1. Fill limiter vent valve stuck open or leaking.
  2. Overfilled fuel tank (topping off fuel tank).

Liquid leak to ground.

Check the following items

  1. Pressure relief valve in fill limiter vent valve is stuck open or leaking.
  2. Fuel filler pipe loose or ruptured.
  3. Leaking fuel tank (seepage).

Fuel odor.

Check the following items

  1. Pressure relief valve is stuck open or leaking.
  2. Saturated EVAP canister.
  3. Seepage from fuel tank.

Engine runs unevenly at idle. If bad enough, vehicle will shake. Idle RPM may vary. Engine idles at incorrect RPM.

Check the following items

  1. Check TP sensor for sticking and binding. Check for correct TP sensor voltage. See FUEL SYSTEMS in appropriate SERVICE & ADJUSTMENT SPECIFICATIONS article.
  2. Check to see if condition is caused by engine running either rich or lean.
  3. Check Park Neutral Position (PNP) switch circuit. Ensure PNP switch is properly adjusted.
  4. Check for poor quality or alcohol contaminated fuel.
  5. Check in-line fuel filter. Replace if dirty or clogged.
  6. Check intake and exhaust manifold passages for casting flash.
  7. Check fuel system for incorrect fuel pressure. See BASIC FUEL SYSTEM CHECKS in appropriate BASIC DIAGNOSTIC PROCEDURES article.
  8. Check fuel injectors. Perform injector balance test. See FUEL INJECTOR BALANCE TEST under FUEL SYSTEMS in appropriate SYSTEM & COMPONENT TESTING article.
  9. Check exhaust system for restrictions, such as a damaged or collapsed pipe, muffler or catalytic converter. See EXHAUST SYSTEM BACKPRESSURE under MECHANICAL INSPECTION in appropriate BASIC DIAGNOSTIC PROCEDURES article.
  10. Check for fuel in pressure regulator vacuum hose. If fuel is present, replace regulator.
  11. Check injector harness locations. Ensure injectors are connected to correct injector/cylinder according to firing order.
  12. If rough idle occurs only when engine is hot, check PCV valve for proper operation. Check evaporative emission control system.
  13. Check engine compression. Check for incorrect valve timing, bent push rods, broken valve springs or worn camshaft lobes.
  14. Using Spark Tester (J-26792), check for adequate spark output.
  15. Remove spark plugs and check for wet plugs, cracks, improper gap, burned electrodes or heavy carbon deposits. Also, check condition of spark plug wires. Spray spark plug wires with a fine mist of water to check for shorts.
  16. Check the Knock System (KS) for excessive spark retard.
  17. Ensure initial ignition timing is properly set.
  18. Check engine idle speed (both base and PCM idle).
  19. Check Idle Air Control (IAC) system. Check for foreign material in IAC bore.
  20. Check EGR system for proper operation.
  21. Check Power Steering Pressure (PSP) switch circuit.

Engine power varies under steady throttle or cruise. Feels like vehicle speeds up and slows down even though accelerator pedal position remains constant.

Check for the following items

  1. Ensure park/neutral switch is properly adjusted.
  2. Check transmission shift solenoid system and Torque Converter Clutch (TCC) system for proper operation.
  3. Ensure owner understands operation of TCC and A/C compressor clutch, as stated in owners manual.
  4. Check exhaust system for restrictions, such as a damaged or collapsed pipe, muffler or catalytic converter. See EXHAUST SYSTEM BACKPRESSURE under MECHANICAL INSPECTION in appropriate BASIC DIAGNOSTIC PROCEDURES article.
  5. Check engine compression. Check for incorrect valve timing, bent push rods, broken valve springs or worn camshaft lobes.
  6. Visually check vacuum hoses for splits, kinks and proper connections as shown on vehicle emission control information label.
  7. Check for proper Crankshaft Position (CKP) and Camshaft Position (CMP) sensor resistance. Check for intermittent ignition feed or ground circuits.
  8. Ensure initial ignition timing is properly set.
  9. Using Spark Tester (J-26792), check for adequate spark output.
  10. Remove spark plugs, and check for wet/fouled spark plugs, cracks in porcelain, improper gap, burned electrodes or heavy carbon deposits. Check spark plug wires.
  11. Check Knock Sensor (KS) system for excessive retard.
  12. Check in-line fuel filter. Replace if dirty or clogged.
  13. Check fuel for water contamination.
  14. Check fuel system for incorrect fuel pressure. See BASIC FUEL SYSTEM CHECKS in appropriate BASIC DIAGNOSTIC PROCEDURES article.
  15. Check fuel injectors. Perform injector balance test. See FUEL INJECTOR BALANCE TEST under FUEL SYSTEMS in appropriate SYSTEM & COMPONENT TESTING article.
  16. Check the HO2 sensors. The HO2 sensors should respond quickly to different throttle positions.
  17. Check the MAF sensor and intake air system for proper connections.
  18. If emission test shows excessive oxides of nitrogen (NOx) emissions, check all systems and components which could cause engine to run lean or to run too hot. Check EGR system. Check for an inoperative cooling fan.
  19. Check canister purge system for proper operation.
  20. Check EGR valve for proper operation.
  21. Check Heated Oxygen Sensor (HO2S) for contamination. This will cause a false high voltage signal to PCM. PCM will respond by leaning out air/fuel ratio.
  22. Check PCM grounds. Ensure they are clean, tight and properly located.
  23. Check charging system output. Repair if output is less than 9 volts or greater than 16 volts.

SYMPTOMS (DIESEL)

Note. Before proceeding with any symptom diagnosis, perform all steps under PRELIMINARY INSPECTION .

Note. If PCM displays data but engine fails to start, see NO-START DIAGNOSIS in appropriate BASIC DIAGNOSTIC PROCEDURES article.

Symptom checks should not be used unless symptom occurs while vehicle is being tested. To reduce diagnostic time, ensure steps in appropriate BASIC DIAGNOSTIC PROCEDURES and SELF-DIAGNOSTICS articles were performed before diagnosing a symptom. Symptoms available for diagnosis include

  1. «Cuts Out &/Or Misses»(/gmc/yukon-denali/gmt800-1999-2006/remont/testing-diagnostics/#engine-controls-trouble-shooting-no-codes)
  2. «Excessive Smoke»(/gmc/yukon-denali/gmt800-1999-2006/remont/testing-diagnostics/#engine-controls-trouble-shooting-no-codes)
  3. «Fuel Knock/Combustion Noise»(/gmc/yukon-denali/gmt800-1999-2006/remont/testing-diagnostics/#engine-controls-trouble-shooting-no-codes)
  4. «Fuel Leaks Or Fuel Smell»(/gmc/yukon-denali/gmt800-1999-2006/remont/testing-diagnostics/#engine-controls-trouble-shooting-no-codes__fuel-leaks-or-fuel-smell)
  5. «Hard Start»(/gmc/yukon-denali/gmt800-1999-2006/remont/testing-diagnostics/#engine-controls-trouble-shooting-no-codes)
  6. «Hesitation, Sag &/Or Stumble»(/gmc/yukon-denali/gmt800-1999-2006/remont/testing-diagnostics/#engine-controls-trouble-shooting-no-codes)
  7. «Lack Of Power, Sluggishness Or Sponginess»(/gmc/yukon-denali/gmt800-1999-2006/remont/testing-diagnostics/#engine-controls-trouble-shooting-no-codes)
  8. «Poor Fuel Economy»(/gmc/yukon-denali/gmt800-1999-2006/remont/testing-diagnostics/#engine-controls-trouble-shooting-no-codes)
  9. «Rough, Unstable, Or Incorrect Idle & Stalling»(/gmc/yukon-denali/gmt800-1999-2006/remont/testing-diagnostics/#engine-controls-trouble-shooting-no-codes)
  10. «Surge &/Or Chuggle»(/gmc/yukon-denali/gmt800-1999-2006/remont/testing-diagnostics/#engine-controls-trouble-shooting-no-codes)

Constant jerking that follows engine speed, usually more pronounced with increased engine load. Not normally felt above 1500 RPM or 30 MPH. Engine has a steady spitting sound at idle or low speed. May cutout under hard acceleration.

Check the following items

  1. Observe the Fuel Rail Pressure (FRP) sensor and the fuel pressure regulator commanded percent at idle. FRP should be near 40 MPa, and commanded percent should be near 40 percent. If the command is high, a fuel pressure or sensor exists.
  2. Inspect for an intermittent Crankshaft Position (CKP) sensor signal.
  3. Inspect the Crankshaft Position (CKP) sensor reluctor wheel. Remove the CKP sensor and attempt to move the reluctor wheel front to back or side to side with a probe. If there is any movement the reluctor wheel retaining bolts are loose.
  4. Check engine for low compression. Check for incorrect valve timing, bent push rods, broken valve springs or worn camshaft lobes.
  5. Inspect valve train for worn or damaged parts.
  6. Check for water contaminated fuel.
  7. Inspect fuel delivery system. Check for low fuel pressure, restriction or air in fuel system. See BASIC FUEL SYSTEM CHECKS (DIESEL) in appropriate BASIC DIAGNOSTIC PROCEDURES article.
  8. Check intake and exhaust manifold passages for casting flash or restrictions.

White, Black, Gray or Blue smoke under load, idle or initial starting hot or cold.

Check the following items

  1. Check fuel quality.
  2. Check fuel injection pump and timing. See appropriate ON-VEHICLE ADJUSTMENTS article.
  3. Observe the actual vs. desired fuel rail pressure with a scan tool, with the engine running.
  4. Check injector nozzles. See appropriate SYSTEM & COMPONENT TESTING article.
  5. Check Engine Coolant Temperature (ECT) sensor. Reading should be within 5°F of ambient air temperature on a cold engine.
  6. Inspect the glow plug system operation.
  7. Inspect the Fuel Rail Pressure (FRP) sensor. Use the scan tool to observe FRP with the engine off. FRP should be 1.1-1.4 MPa. If not, inspect for high resistance in the low reference or 5-volt reference circuits or the sensor.
  8. Check air filter, turbocharger and air intake system for a restriction.
  9. Inspect for contamination of the Mass Air Flow (MAF) sensor.
  10. Perform the engine compression test and a cylinder leakage test.
  11. Inspect the Intake Air Heater (IAH) for proper operation. Use a scan tool to command the IAH on and off.
  12. Check for incorrect basic engine parts such as camshaft, cylinder heads and pistons.
  13. Check for excessive blow-by.
  14. Inspect for coolant entering the combustion chamber.

A mild to severe ping, usually worse under acceleration. Engine makes sharp metallic knocks that change with throttle opening.

Check the following items

  1. Check coolant level. Check cooling system thermostat for proper operation and application.
  2. Check for restricted airflow to radiator or restricted coolant flow through radiator.
  3. Check for loose water pump belt.
  4. Check Engine Coolant Temperature (ECT) sensor, reading should be within 5°F of ambient air temperature on a cold engine.
  5. Inspect the Fuel Rail Pressure (FRP) sensor. Use the scan tool to observe FRP with ignition on and engine off. FRP should be 1.1-1.4 MPa. If FRP is not within this range, check for high resistance in the low reference or 5-volt reference circuits or the sensor, or a faulty sensor.
  6. Inspect for an intermittent Crankshaft Position (CKP) sensor signal.
  7. Inspect CKP sensor reluctor wheel. Remove CKP sensor and attempt to move the reluctor wheel front to back or side to side with a probe. If there is any movement the reluctor wheel retaining bolts are loose.
  8. Check fuel injection pump and timing. See appropriate ON-VEHICLE ADJUSTMENTS article.
  9. Check injector nozzles. See appropriate SYSTEM & COMPONENT TESTING article.
  10. Inspect fuel delivery system. Check for no fuel to injection pump or air in fuel system. See BASIC FUEL SYSTEM CHECKS (DIESEL) in appropriate BASIC DIAGNOSTIC PROCEDURES article.
  11. Check for incorrect basic engine parts such as camshaft, cylinder heads and pistons.
  12. Check for excessive blow-by.

FUEL LEAKS OR FUEL SMELL

See FUEL LEAKS INSIDE OF ENGINE (6.6L) and FUEL LEAKS OUTSIDE OF ENGINE (6.6L) in FUEL SYSTEM (DIESEL) in SYSTEM & COMPONENT TESTING - TRUCKS - EXCEPT TRACKER article.

Engine cranks okay, but does not start for a long time. Engine does eventually run, and may die immediately.

Check the following items

  1. Check engine shutoff solenoid operation. Check electrical connections.
  2. Check air filter, turbocharger and air intake system for a restriction.
  3. Check glow plug operation. Check and/or replace glow plugs or controls.
  4. Check for plugged fuel return system for restrictions.
  5. Check fuel cap vent.
  6. Check for slow engine cranking.
  7. Check engine for low compression. Check for incorrect valve timing, bent push rods, broken valve springs or worn camshaft lobes.
  8. Inspect fuel delivery system. Check for no fuel to injection pump or air in fuel system. See BASIC FUEL SYSTEM CHECKS (DIESEL) in appropriate BASIC DIAGNOSTIC PROCEDURES article.
  9. Inspect the fuel pressure regulator 12-volt circuit for an intermittent short to ground. Observe the FRP command percent while cranking. A range of 85-95 percent indicates a possible short to ground condition.
  10. Check for incorrect or contaminated fuel.
  11. Check for incorrect pump timing. See appropriate SELF-DIAGNOSTICS article.
  12. Check Engine Coolant Temperature (ECT) sensor, Reading should be within 5°F of ambient air temperature on a cold engine.
  13. Inspect the Fuel Rail Pressure (FRP) sensor. Use scan tool to observe FRP with engine off. FRP should be 1.1-1.4 MPa. If not, inspect for high resistance in the low reference, 5-volt reference circuits, or the FRP sensor.
  14. Inspect the Crankshaft Position (CKP) sensor reluctor wheel. Remove CKP sensor and attempt to move reluctor wheel front to back or side to side with a probe. If there is any movement the reluctor wheel retaining bolts are loose.

Vehicle has momentary lack of response when pushing down on accelerator pedal. Condition can occur at any speed but is most noticeable when accelerating from a stop. Condition may cause engine to stall if severe enough.

Check the following items

  1. Check injector nozzles. See appropriate SYSTEM & COMPONENT TESTING article.
  2. Inspect fuel delivery system. Check for no fuel to injection pump or air in fuel system. See BASIC FUEL SYSTEM CHECKS (DIESEL) in appropriate BASIC DIAGNOSTIC PROCEDURES article.
  3. Check for water contaminated fuel.
  4. Inspect for high fuel supply system vacuum after a cold start or during moderate or full throttle acceleration. If the vacuum jumps above specification, there is a restriction in the fuel system.
  5. Observe the Fuel Rail Pressure (FRP) sensor and the fuel pressure regulator commanded percent at idle. FRP should be near 40 MPa, and commanded percent should be near 40 percent. If the command is high, a fuel pressure or sensor exists.
  6. Inspect for an intermittent Crankshaft Position (CKP) sensor signal.
  7. Inspect the CKP sensor reluctor wheel. Remove CKP sensor and attempt to move reluctor wheel front to back or side to side with a probe. If there is any movement the reluctor wheel retaining bolts are loose.
  8. Check charging system output. Repair charging system if voltage is less than 9 volts or more than 16 volts.

The engine delivers less than expected power. There is little or no increase in speed when partially applying the accelerator pedal.

Check the following items

  1. Check injector nozzles. See appropriate SYSTEM & COMPONENT TESTING article.
  2. Inspect fuel delivery system. Check for no fuel to injection pump or air in fuel system. See BASIC FUEL SYSTEM CHECKS (DIESEL) in appropriate BASIC DIAGNOSTIC PROCEDURES article.
  3. Observe the Fuel Rail Pressure (FRP) sensor and the fuel pressure regulator commanded percent at idle. FRP should be near 40 MPa, and commanded percent should be near 40 percent. If the command is high, a fuel pressure or sensor exists.
  4. Inspect the Crankshaft Position (CKP) sensor reluctor wheel. Remove the CKP sensor and attempt to move the reluctor wheel front to back or side to side with a probe. If there is any movement the reluctor wheel retaining bolts are loose.
  5. Check air filter, turbocharger and air intake system for restriction.
  6. Check for incorrect pump timing. See appropriate SELF-DIAGNOSTICS article.
  7. Check oil level and quality.
  8. Inspect fuel quality.
  9. Check control module grounds for correct locations, tight and clean connections. See WIRING DIAGRAMS article.
  10. Inspect the engine speed signal circuit for high resistance.
  11. Check transmission for proper shifting and Torque Converter Clutch (TCC) system for proper operation.
  12. Check engine for low compression. Check for incorrect valve timing, incorrect or worn camshaft.
  13. Inspect fuel delivery system. Check for low fuel pressure, restriction or air in fuel system. See BASIC FUEL SYSTEM CHECKS (DIESEL) in appropriate BASIC DIAGNOSTIC PROCEDURES article.
  14. Check charging system output. Repair charging system if voltage is less than 9 volts or more than 16 volts.
  15. Check A/C for proper operation.
  16. Check for worn or damaged turbocharger turbine wheel, shaft or compressor wheel.
  17. Check for air leaks or restrictions in intake air system or manifold.
  18. Check for a restricted or leaking exhaust system.
  19. Check injector nozzles. See appropriate SYSTEM & COMPONENT TESTING article.

Fuel economy, as measured by an actual road test, is noticeably lower than expected. Current fuel economy is noticeably lower than previous fuel economy.

Check the following items

  1. Check transmission for proper shifting and Torque Converter Clutch (TCC) system for proper operation.
  2. Visually check vacuum hoses for splits, kinks and proper connections as shown on vehicle emission control information label.
  3. Check fuel quality.
  4. Check for dragging brakes.
  5. Check for incorrect tire pressure.
  6. Check with operator to see if vehicle is operated under excessive acceleration or is heavily loaded.
  7. Check A/C for "full time" operation.
  8. Check coolant level. Check engine cooling system thermostat for proper heat range and operation.
  9. Check air filter, turbocharger and air intake system for a restriction.
  10. Inspect fuel delivery system. Check for low fuel pressure, restriction or air in fuel system. See BASIC FUEL SYSTEM CHECKS (DIESEL) in appropriate BASIC DIAGNOSTIC PROCEDURES article.

Engine runs unevenly at idle. If severe, the engine or vehicle may shake. Engine idle speed may vary in RPM. Either condition may be severe enough to stall the engine.

Check the following items

  1. Inspect the PCM grounds for being clean, tight, and in the proper locations.
  2. Remove and inspect the air filter element for dirt or for being restricted.
  3. Inspect the Fuel Rail Pressure (FRP) sensor. Observe the FRP with a scan tool. The FRP should be between 1.1-1.4 MPa. If it is not, inspect for high resistance in the FRP sensor circuits, or the FRP sensor.
  4. Perform the fuel injector balance test. See appropriate SYSTEM & COMPONENT TESTING article.
  5. Inspect for a restriction in the fuel return system.
  6. Inspect for a contaminated fuel condition.
  7. Inspect for a sticking fuel pressure regulator. The symptom for this condition will be an idle surge of at least 100 RPM. This surge will be from 50 RPM above desired idle speed to 50 RPM below desired idle speed.
  8. Observe the Fuel Rail Pressure (FRP) sensor and the fuel pressure regulator commanded percent at idle. FRP should be near 40 MPa, and commanded percent should be near 40 percent. If the command is high, a fuel pressure or sensor exists.
  9. Inspect for an intermittent Crankshaft Position (CKP) sensor signal.
  10. Inspect the Crankshaft Position (CKP) sensor reluctor wheel. Remove the CKP sensor and attempt to move the reluctor wheel front to back or side to side with a probe. If there is any movement the reluctor wheel retaining bolts are loose.
  11. Inspect for proper crankcase ventilation.
  12. Check engine for low compression. Check for incorrect valve timing, bent push rods, broken valve springs or worn camshaft lobes.
  13. Inspect the components of the exhaust system for possible restrictions.
  14. Electromagnetic Interference (EMI) on the reference circuit can cause an engine miss condition. A scan tool can usually detect EMI by monitoring the engine RPM. A sudden increase in RPM with little change in actual engine RPM change indicates that EMI is present. If a problem exists, inspect routing of high voltage components, such as fuel injector wiring, near the sensor circuits.
  15. Inspect the Park/Neutral Position (PNP) switch circuit.
  16. Inspect for a short to 5 volts on one of the fuel injector control circuit between the ECM and the FICM.
  17. Inspect for faulty motor mounts.
  18. Inspect intake manifold and exhaust manifold passages for casting flash.

The engine has a power variation under a steady throttle or cruise. The vehicle seems to speed up and slow down without a change in pressure on the accelerator pedal.

Check the following items

  1. Ensure owner understands operation of TCC and A/C clutch operation, as stated in owners manual.
  2. Check injector nozzles. See appropriate SYSTEM & COMPONENT TESTING article.
  3. Ensure Vehicle Speed Sensor (VSS) reading matches vehicle speedometer reading.
  4. Observe the Fuel Rail Pressure (FRP) sensor and the fuel pressure regulator commanded percent at idle. FRP should be near 40 MPa, and commanded percent should be near 40 percent. If the command is high, a fuel pressure or sensor exists.
  5. Inspect the Crankshaft Position (CKP) sensor reluctor wheel. Remove the CKP sensor and attempt to move the reluctor wheel front to back or side to side with a probe. If there is any movement the reluctor wheel retaining bolts are loose.
  6. Inspect for a sticking fuel pressure regulator. The symptom for this condition will be an idle surge of at least 100 RPM. This surge will be from 50 RPM above desired idle speed to 50 RPM below desired idle speed.
  7. Check charging system output. Repair charging system if voltage is less than 9 volts or more than 16 volts.
  8. Check transmission for proper shifting and Torque Converter Clutch (TCC) system for proper operation.
  9. Check control module grounds for correct locations, tight and clean connections. See WIRING DIAGRAMS article.
  10. Visually check vacuum hoses for splits, kinks and proper connections as shown on vehicle emission control information label.

SYMPTOMS

To trouble shoot the following symptoms, refer to appropriate number under PROBABLE CAUSES .

  1. Engine Lacks Power Check probable causes No. 1 , 3 , 4 , 6 - 11 and 16 - 21 .
  2. Black Smoke Check probable causes No. 2 - 4 , 6 - 11 and 16 - 21 .
  3. Blue Smoke Check probable causes No. 2 , 6 - 8 , 13 - 15 and 17 - 20 .
  4. Excessive Oil Consumption Check probable causes No. 2 , 6 - 8 , 13 - 15 and 17 - 20 .
  5. Noisy Operation Check probable causes No. 1 - 8 , 11 , 12 , 19 and 20 .
  6. Cyclic Sound From Turbocharger Check probable causes No. 2 , 19 and 20 .
  7. Oil Leak At Turbine Seal Check probable causes No. 13 - 15 and 17 - 20 .
  8. Oil Leak At Compressor Seal Check probable causes No. 2 , 8 - 11 , 13 - 15 and 17 - 20 .

PROBABLE CAUSES

  1. Clogged air filter element.
  2. Obstructed air intake duct to turbo compressor.
  3. Obstructed air outlet duct from compressor to intake manifold.
  4. Obstructed intake manifold.
  5. Air leak in duct from air cleaner to compressor.
  6. Air leak in duct from compressor to intake manifold.
  7. Air leak at intake manifold-to-engine joint.
  8. Obstruction in exhaust manifold.
  9. Obstruction in exhaust system.
  10. Gas leak in exhaust manifold-to-engine joint.
  11. Gas leak in turbine inlet-to-exhaust manifold joint.
  12. Gas leak in ducts after turbine outlet.
  13. Obstructed turbocharger oil drain line.
  14. Obstructed engine crankcase ventilation.
  15. Turbocharger center housing sludged or coked.
  16. Engine camshaft timing incorrect.
  17. Worn engine piston rings or liners (blow-by).
  18. Internal engine problems (valves or pistons).
  19. Dirt caked on compressor wheel and/or diffuser vanes.
  20. Damaged turbocharger.
  21. Wastegate stuck open.

INTERMITTENTS

Note. Intermittent is a DTC or symptom, with a condition that cannot be duplicated.

PRELIMINARY

Perform the Diagnostic System Check-Engine Controls before starting. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS in appropriate SELF-DIAGNOSTICS article.

HARNESS OR CONNECTOR INTERMITTENTS

Many intermittent open or shorted circuits come and go with harness or connector movement caused by the following type conditions

  1. Vibration.
  2. Engine torque.
  3. Bumps or rough pavement.

Test for intermittents by performing the applicable procedure from the following list

  1. Move related connectors and wiring while monitoring the appropriate scan tool data.
  2. Move related connectors and wiring with the component commanded on and off, with scan tool. Observe the component operation.
  3. With the engine running, move related connectors and wiring while monitoring engine operation.

Verify whether the harness or connector movement affects any of the following systems

  1. Data displayed.
  2. Component or system operation.
  3. Engine operation.

Repair the components as necessary.

ELECTRICAL CONNECTIONS OR WIRING

  1. Intermittents are usually caused by one or more of the following conditions: Poor electrical connections. Terminal tension. Wiring problems.
  2. Carefully inspect the suspected circuit for the following conditions: Poor mating of the connector halves. Terminals backed out or not fully seated in the connector body. Improperly formed or damaged terminals. Test for poor terminal tension. Poor terminal-to-wire connections including terminals crimped over insulation. This requires removing the terminal from the connector body. Corrosion or water intrusion. Pierced or damaged insulation can allow moisture to enter the wiring. The conductor can corrode inside the insulation, with little visible evidence. Look for swollen and stiff sections of wire in the suspect circuits. Wires that are broken inside the insulation. Pinched, cut or rubbed-through wiring in harness. Wiring that is in contact with hot exhaust components.
  3. Repair the condition as necessary.

CONTROL MODULE POWER & GROUNDS, & COMPONENT POWER & GROUNDS

Poor power or ground connections can cause widely varying symptoms.

  1. Test all control module power circuits. Many vehicles have multiple circuits supplying power to the control module. Other components in the system may have separate power circuits that may also need to be tested. Inspect connections at the module or component connectors, fuses, and any intermediate connections between the power source and the module or component. A test light or a Digital Multimeter (DMM) may indicate that voltage is present, but neither tests the ability of a circuit to carry sufficient current. Ensure that the circuit can carry the current necessary to operate the component. See POWER DISTRIBUTION article in WIRING DIAGRAMS.
  2. Test all control module ground and system ground circuits. The control module may have multiple ground circuits. Other components in the system may have separate grounds that may also need to be tested. Inspect grounds for clean and tight connections at the grounding point. Inspect the connections at the component and in splice packs, where applicable. Ensure that the circuit can carry the current necessary to operate the component. See GROUND DISTRIBUTION article in WIRING DIAGRAMS.

TEMPERATURE SENSITIVITY

  1. An intermittent condition may occur when a component or connection reaches normal operating temperature. The condition may occur only when the component or connection is cold, or only when the connection is hot.
  2. The following data may help to diagnose this type of intermittent condition: Freeze Frame/Failure Records. Scan tool snapshot. Vehicle data recorder.
  3. If the intermittent is related to heat, review the following data: High ambient temperatures. Underhood or engine generated heat. Circuit generated heat due to a poor connection, or high electrical load. Higher than normal load conditions, such as towing.
  4. If the intermittent is related to cold, review the following data: Low ambient temperatures. In extremely low temperatures, ice may form in a connection or component. Test for water intrusion. The condition only occurs on a cold start. The condition is not present after the vehicle warms up.
  5. Information from the customer may help to determine if the trouble follows a pattern that is temperature related.

ELECTROMAGNETIC INTERFERENCE (EMI) & ELECTRICAL NOISE

Some electrical components or circuits are sensitive to Electromagnetic Interference (EMI) or other types of electrical noise. Perform the following procedures

  1. Inspect for a misrouted harness that is too close to a high voltage or high current device. This condition may induce electrical noise on a circuit that could interfere with normal circuit operation. Inspect for wires that are too close to the following devices: Secondary ignition components. Motors. The generator.
  2. Determine whether the electrical system interference is caused by a malfunctioning relay, PCM driven solenoid or switch. These components may cause a sharp electrical surge. Normally, the problem will occur when the malfunctioning component is operating.
  3. Determine whether non-factory or aftermarket add-on accessories are installed in the vehicle. These accessories may lead to an emission related OBD-II failure. Determine if any of the following non-factory or aftermarket add-on accessories is causing the intermittent: Lights. 2-way radios. Amplifiers. Electric motors. Remote starters. Alarm systems. Cell phones.
  4. Test for an open diode across the A/C compressor clutch and for other open diodes. Some relays may contain a clamping diode.
  5. Test for proper performance of the generator. See ON-VEHICLE TESTING in appropriate GENERATORS & REGULATORS article in STARTING & CHARGING SYSTEMS.
  6. If a DTC is determined to be intermittent, and the tests in this section do not reveal a problem, see «VEHICLE DATA RECORDER»(/gmc/yukon-denali/gmt800-1999-2006/remont/testing-diagnostics/#engine-controls-trouble-shooting-no-codes__vehicle-data-recorder) .

INCORRECT PCM PROGRAMMING

  1. There are only a few situations when reprogramming a PCM is appropriate, such as the following: A new service PCM is installed. A PCM from another vehicle is installed. Revised software or calibration files have been released for this vehicle.
  2. Verify that the PCM contains the correct software or calibration. If incorrect programming is found, reprogram the PCM with the most current software or calibration. See POWERTRAIN CONTROL MODULE under PROGRAMMING in appropriate SELF-DIAGNOSTICS article.

DUPLICATING FAILURE CONDITIONS

  1. If none of the previous tests are successful, attempt to duplicate or capture the failure conditions.
  2. Freeze Frame/Failure Records data, where applicable, contains the conditions that were present when the DTC set. Perform the following procedure: Review and record Freeze Frame/Failure Records data. Clear DTCs using scan tool. Turn ignition off and wait 15 seconds. Operate vehicle under the same conditions that were noted in Freeze Frame/Failure Records data, as closely as possible. The vehicle must also be operating within the Conditions for Running DTC. Monitor DTC Status for the DTC being tested. The scan tool will indicate Ran, when the enabling conditions have been satisfied long enough for the DTC to run. The scan tool will also indicate whether the DTC passed or failed.
  3. An alternate method is to drive the vehicle with the Digital Multimeter (DMM) connected to a suspected circuit. An abnormal reading on the DMM when the problem occurs, may help you locate the problem.

SCAN TOOL SNAPSHOT

The scan tool can be set up to take a snapshot of the parameters available via serial data. The snapshot function records live data over a period of time. The recorded data can be played back and analyzed. The scan tool can also graph parameters singly or in combinations of parameters for comparison. The snapshot can be triggered manually at the time the symptom is noticed, or set up in advance to trigger when a DTC sets. An abnormal value captured in the recorded data may point to a system or component that needs to be investigated further. Refer to the scan tool user instructions for more information on the Snapshot function.

VEHICLE DATA RECORDER

The Vehicle Data Recorder (J-42598) is connected to the Data Link Connector (DLC) and sent with customer. The vehicle data recorder captures data for later retrieval and analysis by the technician. Refer to vehicle data recorder user instructions for more information.

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