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Tahoe / Yukon Service Manual

Symptoms - Engine Controls

Engine Controls and Fuel - 3.0L LM2 Diesel | Diagnostic Information and Procedures | Document ID: 5641962 Diagnostic Instructions Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Review Strategy Based Diagnosis for an overview of the diagnostic approach. Diagnostic Procedure Instructions provide an overview of each diagnostic category. Symptoms Description Symptoms covers conditions that are not covered by DTCs. Certain conditions can cause multiple symptoms. These conditions are listed together under Symptoms Testing. Conditions that may only cause specific symptoms are listed separately under Additional Symptoms Testing. Perform the Symptoms Testing before using the Additional Symptoms Testing. Symptoms Definition Cuts Out, Misses A steady pulsation or jerking that follows engine speed, which is usually more pronounced as the engine load increases. This condition is not normally felt above 1500 RPM or 48 km/h (30 mph). The exhaust has a steady spitting sound at idle or at low speed. Engine Control Module (ECM) Reduced Engine Power The ECM illuminates the Reduced engine Power lamp and will limit engine power under potential engine/vehicle damaging or emissions related conditions. A DTC may not be set. Excessive Smoke (Black) Black smoke under load, idle or start up, hot or cold. Excessive Smoke (Gray or Blue) Gray or Blue smoke under load, idle or start up, hot or cold. Excessive Smoke (White) White smoke under load, idle or start up, hot or cold. Fuel Knock/Combustion Noise A mild to severe ping, usually worse under acceleration. The engine makes sharp metallic knocks that change with the throttle opening. Hard Start The engine cranks OK, but does not start for a long time. The vehicle does eventually run, or may start but immediately stall. Hesitation, Sag, Stumble A momentary lack of response as the accelerator is pushed down. This condition can occur at any vehicle speed. This condition is usually more pronounced when first trying to make the vehicle move, as from a stop. This condition may cause the engine to stall in severe conditions. Lack of Power, Sluggishness, or Sponginess The engine delivers less than expected power. Little or no increase in vehicle speed when the accelerator pedal is pushed down part way. Poor Fuel Economy Fuel economy, as measured by an actual road test, is noticeably lower than expected. Also, the fuel economy is noticeably lower than it was on this vehicle at one time, as previously shown by an actual road test. Rough, Unstable, or Incorrect Idle and Stalling The engine runs unevenly at idle. If severe, the engine or the vehicle may shake. Engine idle speed may vary. Either condition may be severe enough to stall the engine. Surges/Chuggles An engine power variation under steady throttle or cruise. Feels like the vehicle speeds up and slows down with no change in the accelerator pedal position. Symptoms Verification Before using the Symptom tables, perform the following inspections: Verify that the engine control module (ECM) and malfunction indicator lamp (MIL) are operating correctly. Use the scan tool to command the MIL ON and OFF. Verify that there are no DTCs that are stored. Verify that the scan tool data is within a normal operating range. Refer to Control Module References for scan tool information. Verify the customer concern. Perform the Visual/Physical Inspection in this section. The visual/physical inspection is extremely important, and can lead to correcting a condition without additional testing. It may also help reveal the cause of an intermittent condition. Identifying Intermittent Conditions Many intermittent conditions occur with harness or connector movement due to engine torque, rough pavement, vibration or physical movements of a component. Refer to the following for a list of issues that may cause an intermittent condition: Moisture and water intrusion in connectors, terminals, and components Incomplete connector mating Poor terminal contact High circuit or component resistance—High resistance can include any resistance, regardless of the amount, which can interrupt the operation of the component. Harness that is too short or tight Wire insulation that is chaffed or cut High or low ambient temperature High or low engine coolant temperatures High underhood temperatures Heat build up in component or circuit due to circuit resistance, poor terminal contact, or high electrical load High or low system voltage High vehicle load conditions Rough road surfaces Electro-magnetic interference (EMI)/circuit interference from relays, solenoids or other electrical surge Incorrect installation of aftermarket, add on accessories Visual/Physical Check Verify that the control module grounds are clean, tight, and correctly located. Refer to Component Connector End Views. Verify that the air filter is clean and free from restrictions. Verify that there is no water intrusion in connectors terminals and components. Inspect the air intake ducts for the following conditions: – Collapsed – Damaged areas – Looseness – Incorrect installation – Leaking Inspect for air leaks at the intake AIR valve, the intake AIR heater, the MAF sensor and intake manifold sealing surfaces. Inspect the wiring harness for the following conditions: – Poor connections – Pinches – Cuts Inspect for loose, damaged, unseated, or missing sensors/components. Inspect the terminals for corrosion and correct contact. Symptoms Testing Cuts Out/Misses, Engine Control Module (ECM) Commanded Reduced Engine Power, Fuel Knock/Combustion Noise, Hard Start, Hesitation/Sag/Stumble, Lack of Power/Sluggishness/Sponginess, Poor Fuel Economy, Rough, Unstable, or Incorrect Idle and Stalling, Surges/Chuggles, or Excessive Smoke (Black), Excessive Smoke (White), Excessive Smoke (Gray or Blue)

  1. Test for the following conditions: The sensor systems for the following: – Inspect the mass air flow (MAF) sensor for obstruction, contamination, and damage. – Idle the engine and observe the Actual Fuel Rail Pressure and the Desired Fuel Rail Pressure parameters. If the pressure difference is more than 2 MPa, a fuel control issue may exist. – Inspect for the EGR valve sticking open. Command the valve to 20%. Desired and actual position should not be more than 3% different. – Inspect the 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. – Inspect the engine coolant temperature (ECT) sensor. Use the scan tool in order to compare the ECT with the ambient air temperature on a cold engine. If the coolant temperature reading is more than 5 degrees more or less than the ambient air temperature on a cold engine, inspect for a high resistance in the coolant sensor circuit or the sensor itself. – Inspect for an intermittent Fuel Rail Pressure sensor signal by wiggling the harness between the sensor and the ECM with the ignition ON and the engine OFF, while monitoring the parameter with a scan tool. – Inspect for an intermittent crankshaft position (CKP) sensor signal. Refer to Testing for Intermittent Conditions and Poor Connections. The Air Induction System for the following: – Leaks in the Induction system before the Turbocharger. Refer to Induction System Smoke Test in Charge Air Cooler Diagnosis. – Leaks in the Charge Air Cooler system. Refer to Charge Air Cooler Diagnosis. – Leaks in the engine assembly. Refer to Full System Air Leak Test in Charge Air Cooler Diagnosis. The Fuel System for the following: – Inspect for external fuel leaks. Refer to Fuel Leak Diagnosis. – Inspect the fuel quality. Refer to Contaminants-in-Fuel Diagnosis and Fuel System Specifications. – Inspect for the proper fuel pressure. Refer to Fuel System Diagnosis. – Inspect for proper fuel system return line pressure. Refer to Fuel Return System Diagnosis. – Inspect the engine speed signal circuit for high resistance. – If the ECM or a fuel injector has recently been replaced, it may be necessary to confirm the fuel injector flow rate values. Refer to Fuel Injector Flow Rate Programming. – Inspect the fuel tank cap vent for proper operation. Engine mechanical for the following. – Improper valve timing – Low engine compression—Refer to Engine Compression Test. – Broken or weak valve springs – Worn camshaft lobes—Refer to Camshaft Housing Overhaul. – Excessive oil in the combustion chamber—Leaking valve seals—Refer to Oil Consumption Diagnosis.  2. If the above conditions do not address the symptom, refer to the additional symptoms tests. Additional Symptoms Tests ECM Commanded Reduced Engine Power Under certain conditions the engine control module may limit engine power by reducing engine torque and, for some vehicles, fuel pressure as well. For most, but not all of the conditions, the engine control module will illuminate the reduced engine power lamp on the instrument cluster. If equipped with the driver information center feature, a reduced engine power message may be displayed as well. A DTC may not be set. A repair may not be necessary. Observe the scan tool Reduced Engine Power History parameter or refer to K20 Engine Control Module: Scan Tool Information to determine the reason for the reduced engine power event. Verify or inspect for the following: Vehicle being operated at sustained high engine speeds, or, towing heavy loads up an incline for an extended period of time, which may cause the engine oil or coolant to overheat. Inspect the airflow passageways in front of the engine for obstructions and clear away any debris or foreign material that is found. If no obstructions are found, review approved driving habits with the customer. The customer may need to operate the vehicle at a higher engine speed to improve cooling system performance, or, at a slower engine speed to reduce engine load. A cooling fan condition which may cause the ECM to reduce engine power. Refer to Cooling Fan Description and Operation and Cooling System Description and Operation to verify correct operation of the cooling fan. Reduced engine power due to OnStar® remote command. Verify the vehicle is not in the OnStar® initiated Stolen Vehicle Slowdown mode. . Refer to OnStar Stolen Vehicle Slowdown Active and Remote Vehicle Speed Limiting Description and Operation. Maximum recommended engine oil life exceeded. Refer to the Owners manual for scheduled maintenance recommendations. High pressure fuel system fuel pressure condition. Refer to Fuel System Diagnosis, Fuel System Description and Fuel System Specifications to verify high pressure fuel system operation. Turbocharger boost pressure out of range. Refer to Compressor Air Intake Turbocharger System Description. A diesel exhaust after treatment system condition. Refer to Exhaust Aftertreatment System Description. A diesel exhaust after treatment reductant fluid condition. Inspect for any of the conditions listed below: – Reductant system malfunction. Verify the correct operation of the system and inspect for tampering. Refer to Diesel Exhaust Fluid (DEF) Warning Strategy and Reductant System Tamper Service Bay Test. – Reductant fluid contaminated, poor quality, or level too low. Refer to Contaminants-in- Diesel Exhaust Fluid Diagnosis. Fuel Knock/Combustion Noise Inspect for obvious overheating problems. Refer to Engine Overheating. Inspect for a low engine coolant level. Inspect for any restricted air flow through the radiator. Refer to Engine Radiator Cleaning. Inspect for a malfunctioning or incorrect thermostat. Inspect for a correct coolant solution. The solution should be a 50/50 mix of anti-freeze and water. Hard Start Inspect for a slow cranking speed. Refer to Symptoms - Engine Electrical. Verify the engine electrical system for correct operation. Refer to Symptoms - Engine Electrical. Verify that the driver is using the correct starting procedure as described in the owners manual. Inspect for a restriction in turbocharger inlet duct. Inspect for a restriction or a leak in the intake manifolds. Inspect the exhaust system for a possible restriction. Refer to Restricted Exhaust. Inspect for excessive crankshaft endplay that will cause the CKP sensor reluctor wheel to move out of alignment with the CKP sensor. Hesitation, Sag, Stumble Test the generator. Refer to Symptoms - Engine Electrical. Repair the charging system if the generator output voltage is less than 9 volts or more than 16 volts. Inspect for excessive crankshaft endplay that will cause the CKP sensor reluctor wheel to move out of alignment with the CKP sensor. Lack of Power, Hesitation, or Cut Out Compare the vehicle with a similar unit. Ensure the vehicle has an actual problem. Inspect the engine oil level and quality. Inspect for auxiliary fuel filters. Aftermarket fuel filters may restrict fuel flow. Inspect for a skewed mass air flow (MAF) sensor. Refer to Diagnostic Aids in DTC P0101. Inspect for proper transmission operation. Inspect for a restriction in the charge air cooler. Refer to Charge Air Cooler Diagnosis Inspect for an air leak in the charge air cooler. Refer to Charge Air Cooler Diagnosis. Inspect the engine electrical system for correct operation. Refer to Symptoms - Engine Electrical. Inspect for a worn or damaged turbocharger turbine wheel, shaft or compressor wheel. Inspect that the exhaust gas recirculation (EGR) valve is fully closing. Remove the EGR valve and visually inspect that there is no light seen between the valves and the valve seats. Verify that the EGR valve does not bind when manually moving the valve. Inspect the torque converter clutch (TCC) operation. Inspect the air conditioning system for proper operation. Refer to Air Conditioning (A/C) System Performance Test. Inspect the exhaust system for a possible restriction. Poor Fuel Economy Suggest to the driver to read the Important Facts on Fuel Economy in the Owner Manual. Confirm proper interpretation of the Average Fuel Economy value on the DIC. The Fuel Economy value should be reset periodically. Particularly if driving patterns, including load, terrain, etc., have changed significantly since the last Fuel Economy Reset. Suggest to the owner to fill the fuel tank and inspect the fuel economy. The following conditions can reduce fuel economy: – Aftermarket body accessories that can affect wind flow over the vehicle. Including air deflectors, flares, etc. – Heavy loads being carried or towed, or the shape of large loads – Extended idle time – Acceleration rate too much or too often – Incorrect tire size or air pressure – Improper fuel quality and rating—Refer to Contaminants-in-Fuel Diagnosis and Fuel System Specifications. – Aftermarket ECM calibrations – Certain aftermarket air filters or air induction systems – An air leak in the induction or engine systems—Refer to full system air leak test in Charge Air Cooler Diagnosis. – Fuel system issues—Inspect the injector balance rates. Balance rates should be between +4 mm³ and -6.9 mm³ in Park or Neutral. – Brake system drag – Air conditioning system improper operation – Incorrect operation of the speedometer Rough, Unstable, or Incorrect Idle and Stalling Inspect the engine mounts. Inspect the intake and exhaust manifolds for casting flash. The exhaust system for damaged or collapsed pipes The exhaust manifold for a collapsed inner wall The mufflers for heat distress or possible internal failure 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. Inspect the park neutral position (PNP) switch circuit. Surges/Chuggles Verify the driver understands the torque converter clutch (TCC) operation. Verify the driver understands the A/C compressor operation. Use the scan tool to ensure the vehicle speed sensor (VSS) reading matches the speedometer. This excludes vehicles with electronic transmissions where some variation between VSS and the speedometer is normal. Excessive Smoke (Black) The DPF is damaged and must be replaced. Inspect the following possible causes that may have damaged the DPF. Inspect for an air leak in the charge air cooler or the air ducts between the turbocharger and the intake manifold. Refer to Charge Air Cooler Diagnosis. Inspect for a restriction in the turbocharger charge air cooler. Inspect for a restriction in the intake manifold. Inspect for excessive oil entering the combustion chamber. Refer to Oil Consumption Diagnosis. Inspect for a stuck open EGR valve. Refer to Exhaust Gas Recirculation Valve Replacement - Exhaust Manifold. – Visually inspect the EGR valve and verify the valve is in the closed position. – Verify that the EGR valve does not bind when manually moving the valve. Excessive Smoke (White) Check the coolant level in the reservoir. White coolant smoke may be mistaken for blue/gray smoke. If the coolant level is low, refer to Loss of Coolant. If excessive smoke is present, inspect for a stuck open fuel injector. Refer to: Fuel System Diagnosis If the ECM glow plug control module (GPCM) or a fuel injector has recently been replaced, it may be necessary to confirm the fuel injector flow rate values. Refer to Fuel Injector Flow Rate Programming. Excessive Smoke (Blue, Gray, or White) Blue, gray, or white smoke during regeneration may indicate a fuel with high sulfur content.