Symptoms - Engine Controls (KO7)
Symptoms - Engine Controls (LC8\KO7)
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis Strategy Based Diagnosis for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions Diagnostic Procedure Instructions provides an overview of each diagnostic category.
Symptoms Description
Symptoms cover 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 certain symptoms are listed separately under Additional Symptoms Test. Perform the Symptoms Testing before using the Additional Symptoms Tests.
Symptoms Definition
Backfire
- Fuel ignites in the intake manifold or in the exhaust system, making a loud popping noise.
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.
Detonation/Spark Knock
- A mild to severe ping which usually occurs worse while under acceleration. The engine makes sharp metallic knocks that change with throttle opening.
Engine Control Module (ECM) Commanded Reduced Engine Power
- The ECM illuminates the Reduced Engine Power lamp and will limit engine power under potential engine damaging or emissions related conditions. A DTC may not be set.
Dieseling, Run-On
- The engine continues to run after the key is turned OFF, but runs very rough.
Hard Start
- Engine cranks OK, but does not start for a long time. The vehicle does eventually run, or may start but immediately stalls.
Hesitation, Sag, Stumble
- 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 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.
Reduced Vehicle Range
- The distance that the vehicle can be driven, before running out of fuel, is reduced.
Rough, Unstable, or Incorrect Idle and Stalling
- The engine runs unevenly at idle. If severe, the engine or the vehicle may shake. Engine idle may vary in speed. Either condition may be severe enough to stall the engine.
Surges/Chuggles
- 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 and malfunction indicator lamp (MIL) are operating correctly.
* Verify that there are no DTCs that are stored.
* Verify that the scan tool data is within a normal operating range.
* 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 engine control module grounds are clean, tight, and correctly located. Refer to Wiring Repairs Wiring Repairs.
* Verify that the vacuum hoses are not split or kinked, and are properly connected, as shown on the Vehicle Emission Control Information label.
* 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 throttle body mounting area, the mass air flow sensor and intake manifold sealing surfaces.
* Inspect the fuel system lines and components for damage or external fuel leaks.
* 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
Backfire, Cuts Out/Misses, Detonation/Spark Knock, Dieseling/Run-On, Engine Control Module (ECM) Commanded Reduced Engine Power, Hard Start, Hesitation/Sag/Stumble, Lack of Power/Sluggishness/Sponginess, Poor Fuel Economy, Rough, Unstable, or Incorrect Idle and Stalling, or Surges/Chuggles
1. Test for the following conditions:
* The fuel system for the following:
- Leaking or improperly operating fuel system components-Refer to Fuel System Description (LC8\K07\UFP) Description and OperationFuel System Description (LC8\FHZ) Description and OperationFuel System Description (LC8\K07\UFM) Description and OperationFuel System Description (Without LC8) Description and Operation and Fuel System Diagnosis (Without FPCM) Testing and InspectionFuel System Diagnosis (LC8\K07\UFP) Testing and InspectionFuel System Diagnosis (LC8\FHZ) Testing and InspectionFuel System Diagnosis (FPCM) Fuel System DiagnosisFuel System Diagnosis (LC8\K07\UFM) Testing and Inspection.
- Improperly operating fuel injectors. A fuel injector condition may cause an engine misfire or other condition without setting a fuel injector DTC. Monitor the engine misfire current counters if misfire is suspected and refer to Fuel Injector Diagnosis (LC8\FHZ) Testing and InspectionFuel Injector Diagnosis (J 39021 or Tech 2) Fuel Injector DiagnosisFuel Injector Diagnosis (CH47976) Fuel Injector DiagnosisFuel Injector Diagnosis (LC8\K07) Testing and Inspection for additional information.
* The ignition system for the following:
- Spark plugs with incorrect heat range or an abnormal condition-Refer to Spark Plug Inspection Testing and Inspection.
- Coolant or oil fouled spark plugs-Refer to Loss of Coolant Loss of Coolant or Symptoms - Engine Mechanical.
- Secondary ignition system susceptible to moisture. With the engine running, wet down the secondary ignition system with water from a spray bottle in order to help locate damaged or deteriorated components. Look/listen for arcing or misfiring as the water is applied.
- Weak spark using the J 26792 - HEI Spark Tester-Refer to Electronic Ignition System Diagnosis Electronic Ignition (EI) System Diagnosis.
* Improper operation of the transmission torque converter clutch (TCC)-The scan tool should indicate an engine speed drop when the TCC is commanded ON.
* Improper operation of the A/C compressor
* Items that can cause an engine to run rich or lean-Refer to DTC P0171, P0172, P0174, or P0175 P0171.
* Slow responding heated oxygen sensors (HO2S). The heated oxygen sensors should respond quickly to different throttle positions.
Caution: Refer to Heated Oxygen and Oxygen Sensor Caution Service Precautions.
* Water intrusion in the heated oxygen sensor connector
Note: The embossed arrows on the mass air flow sensor indicate the direction of the intake air flow. The arrows must point toward the engine.
* Improper mass air flow sensor installation. A mass air flow sensor that is incorrectly installed may cause a hard start. Install the mass air flow sensor in the proper direction. Refer to Mass Airflow Sensor with Intake Air Temperature Sensor Replacement Service and Repair.
* Loose or improper mass air flow sensor connections.
* Split or kinked vacuum hoses-Verify that the routing and connections are as shown on the Vehicle Emission Control Information label.
* Excessive knock sensor system spark retard activity-Refer to DTC P0324, P0325, P0326, P0327, P0328, P0330, P0332, or P0333 P0324.
* The exhaust system components for the following:
- Physical damage or possible internal failure
- Restricted three-way catalytic converters
- More Information-Refer to Symptoms - Engine Exhaust Testing and Inspection.
* Electromagnetic interference on the reference circuit can cause a misfire condition. You can usually detect EMI with a scan tool by monitoring the engine speed parameter. A sudden increase in the engine speed parameter with little change in actual engine speed indicates that electromagnetic interference is present. Inspect the high voltage components near the ignition control circuit if a condition exists.
* Improper operation of the crankcase ventilation valve-Refer to Crankcase Ventilation System Inspection/Diagnosis Testing and Inspection.
* The engine cooling system for the following conditions:
- A thermostat with incorrect heat range. Refer to Thermostat Diagnosis Thermostat Diagnosis.
- Improper engine coolant level-Refer to Cooling System Draining and Filling (Static Fill) Cooling System Draining and Filling (Static Fill)Cooling System Draining and Filling (Vac N Fill) Cooling System Draining and Filling (Vac N Fill)Cooling System Draining and Filling (Static Fill Diesel) Cooling System Draining and Filling (Static Fill Diesel).
* The engine for the following mechanical conditions:
- Excessive oil in the combustion chamber or leaking valve seals
- Incorrect cylinder compression
- Sticking or leaking valves
- Worn camshaft lobes
- Incorrect valve timing
- Worn rocker arms
- Broken valve springs
- Excessive carbon buildup in the combustion chambers-Clean the chambers with top engine cleaner, if necessary. Follow the instructions on the can.
- Incorrect engine parts
- More information-Refer to Symptoms - Engine Mechanical Symptoms - Engine Mechanical.
2. If the above conditions do not address the symptom, refer to the additional symptoms tests.
Additional Symptoms Tests
Detonation/Spark Knock
* Test the engine for an overheating condition. Refer to Symptoms - Engine Cooling Symptoms - Engine Cooling.
* Verify that the engine coolant temperature sensor has not shifted in value. Allow the engine to run and reach operating temperature. Observe the scan tool ECT Sensor parameter and compare the reading to that parameter listed on the Engine Control Module Scan Tool Information (LU3) Scan Tool Testing and ProceduresEngine Control Module Scan Tool Information (Compressed Natural Gas) Scan Tool Testing and ProceduresEngine Control Module Scan Tool Information (V8 Gasoline) Scan Tool Testing and ProceduresEngine Control Module Scan Tool Information (LGH or LML) Scan Tool Testing and Procedures list. If the reading is not in the range specified in the list, test the resistance of the engine coolant temperature sensor. Refer to Temperature Versus Resistance [1][2]Computers and Control Systems for resistance specifications. Replace the engine coolant temperature sensor if the resistance is not within specification. Refer to Engine Coolant Temperature Sensor Replacement Service and Repair. If the sensor is within the specification, test the engine coolant temperature sensor circuits for high resistance.
* Inspect for excessive carbon buildup in the combustion chambers. Clean the chambers with Top Engine Cleaner, if necessary. Follow the instructions on the can.
Engine Control Module (ECM) Commanded Reduced Engine Power
Under certain conditions the engine control module may limit engine torque to reduce engine power. For most, but not all of the conditions, the engine control module will illuminate the reduced engine power lamp on the instrument panel cluster. However, a DTC may not be set. Observe the scan tool Reduced Engine Power History parameter or refer to Engine Control Module Scan Tool Information (LU3) Scan Tool Testing and ProceduresEngine Control Module Scan Tool Information (Compressed Natural Gas) Scan Tool Testing and ProceduresEngine Control Module Scan Tool Information (V8 Gasoline) Scan Tool Testing and ProceduresEngine Control Module Scan Tool Information (LGH or LML) Scan Tool Testing and Procedures 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. A repair may not be necessary. 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 (w/LGH) Description and Operation and Cooling System Description and Operation Description and Operation to verify correct operation of the cooling fan.
* Reduced engine power due to OnStar(R) remote command. Verify the vehicle is not in the OnStar(R) initiated Stolen Vehicle Slowdown mode. Refer to OnStar Stolen Vehicle Slowdown Active Testing and Inspection and Remote Vehicle Speed Limiting Description and Operation Description and Operation for additional information.
* An incorrect learned brake pedal position (BPP) sensor. Verify the following actions have not occurred:
- An engine control module (ECM) has been replaced
- A BPP sensor has been replaced
- A BPP sensor is misaligned or incorrectly installed
If any of the above actions have occurred, perform the appropriate brake pedal position learn procedure:
* If equipped with transmission MYD, perform the Brake Pedal Position Sensor Learn Testing and Inspection
* If equipped with transmission M30, perform the Brake Pedal Position Sensor Learn Testing and Inspection
Hard Start
* Observe the Throttle Body Idle Airflow Compensation parameter with a scan tool. A value greater than 90 % may indicate an excessive accumulation of deposits in the throttle bore. Inspect the throttle body and bore and clean, if necessary. Refer to Throttle Body Cleaning Service and Repair.
* Test the engine coolant temperature sensor. Compare the scan tool ECT Sensor parameter value to the intake air temperature (IAT) sensor value on a cold engine. The ECT and IAT Sensor values should be within ± 3°C (5°F). If the engine coolant temperature sensor is out of range with the intake air sensor, test the resistance of the engine coolant temperature sensor. Refer to Temperature Versus Resistance [1][2]Computers and Control Systems for resistance specifications. Replace the engine coolant temperature sensor if the resistance is not within specification. Refer to Engine Coolant Temperature Sensor Replacement Service and Repair. If the sensor is within the specification, test the engine coolant temperature sensor circuits for a high resistance.
Note: The LPG fuel system is designed to inject liquid propane into the combustion chambers. However, because propane easily vaporizes into a gas, the system goes through a purge cycle before every start-up attempt in order to expel any vapor that may have accumulated. If a condition exists which affects the purge cycle, the engine may require cranking for an extended period of time before it will start and run.
* Verify proper operation of the fuel system and the purge cycle. Refer to Fuel System Description (LC8\K07\UFP) Description and OperationFuel System Description (LC8\FHZ) Description and OperationFuel System Description (LC8\K07\UFM) Description and OperationFuel System Description (Without LC8) Description and Operation and Fuel System Diagnosis (Without FPCM) Testing and InspectionFuel System Diagnosis (LC8\K07\UFP) Testing and InspectionFuel System Diagnosis (LC8\FHZ) Testing and InspectionFuel System Diagnosis (FPCM) Fuel System DiagnosisFuel System Diagnosis (LC8\K07\UFM) Testing and Inspection.
Hesitation, Sag, Stumble
* Test the manifold absolute pressure sensor. Refer to DTC P0106 P0106.
* 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.
* Verify proper operation of the fuel system. Refer to Fuel System Description (LC8\K07\UFP) Description and OperationFuel System Description (LC8\FHZ) Description and OperationFuel System Description (LC8\K07\UFM) Description and OperationFuel System Description (Without LC8) Description and Operation and Fuel System Diagnosis (Without FPCM) Testing and InspectionFuel System Diagnosis (LC8\K07\UFP) Testing and InspectionFuel System Diagnosis (LC8\FHZ) Testing and InspectionFuel System Diagnosis (FPCM) Fuel System DiagnosisFuel System Diagnosis (LC8\K07\UFM) Testing and Inspection.
Poor Fuel Economy
* Inspect for heavy loads being carried or towed.
* Inspect for acceleration rate too much or too often.
* Observe the Throttle Body Idle Airflow Compensation parameter with a scan tool. A value greater than 90 % may indicate an excessive accumulation of deposits in the throttle bore. Inspect the throttle body and bore and clean, if necessary. Refer to Throttle Body Cleaning Service and Repair.
Reduced Vehicle Range (UFP)
If a condition exists which prevents fuel from being transferred from the secondary fuel tanks to the main fuel tank, vehicle driving range may be greatly reduced. Refer to Fuel Transfer Pump Diagnosis (LC8\K07\UFP) Testing and Inspection.
Rough, Unstable, or Incorrect Idle and Stalling
* Observe the Throttle Body Idle Airflow Compensation parameter with a scan tool. A value greater than 90 % may indicate an excessive accumulation of deposits in the throttle bore. Inspect the throttle body and bore and clean, if necessary. Refer to Throttle Body Cleaning Service and Repair.
* Inspect the engine mounts. Refer to Engine Mount Inspection Testing and Inspection.
Surges/Chuggles
* Inspect for slow responding heated oxygen sensors. The heated oxygen sensors should respond quickly to a change in throttle position. If the heated oxygen sensors do not respond to different throttle positions, inspect for contamination from fuel, silicon, or the incorrect use of RTV sealant. The sensors may have a white powdery coating and result in a high, but false, signal voltage, which gives a rich exhaust indication. The engine control module reduces the amount of fuel delivered to the engine, causing a driveability condition.
* Inspect the mass air flow sensor for obstruction, contamination, and damage. Refer to Mass Airflow Sensor with Intake Air Temperature Sensor Replacement Service and Repair.
* Verify that each injector harness is connected to the correct injector.