Symptoms - Engine Controls
Symptoms - Engine Controls
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 specific symptoms are listed separately under additional symptoms testing. Perform the symptoms testing before using the additional symptoms testing.
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 1 500 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 gets 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/vehicle damaging or emissions related conditions. A DTC may not be set.
Dieseling, Run-On
- Fuel ignites in the intake manifold or in the exhaust system, making a loud popping noise.
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.
Poor Fuel Fill Quality
- Difficulty when refueling the vehicle.
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 malfunction indicator lamp (MIL) is operating correctly. Use the scan tool to command the lamp 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 Control Module References for scan tool information.
* Verify the customer concern.
* Verify there are no Bulletins for the current symptom.
* Verify that the vehicle tires are correctly inflated and meet original equipment specifications.
* 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.
* 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 (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
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:
* An incorrectly operating fuel system. Test for the following:
- Correct fuel pressure-Refer to Fuel System Diagnosis Fuel System Diagnosis.
- Fuel injectors that are leaking or improper operation-Refer to Fuel Injector Diagnosis Fuel Injector Diagnosis.
- Contaminated or a poor fuel quality condition-Refer to Alcohol/Contaminants-in-Fuel Diagnosis Alcohol/Contaminants-in-Fuel Diagnosis.
* An incorrectly operating ignition system. Test or inspect for the following:
- Spark plugs with an incorrect heat range or an abnormal condition-Refer to Spark Plug Replacement Service and Repair.
- Coolant or oil fouled spark plugs-Refer to Spark Plug Inspection Testing and Inspection and Ignition System Specifications Application and ID.
- Secondary ignition system susceptible to moisture-Engine running, wet down the secondary ignition system with water from a spray bottle to help locate damaged or deteriorated components. Look/listen for arcing or misfiring as the water is applied.
- Weak spark using the EL 26792 - HEI Spark Tester-For equivalent regional tools, refer to Special Tools Tools and Equipment. Refer to Electronic Ignition System Diagnosis Electronic Ignition System Diagnosis.
* An incorrectly operating A/C compressor
* Items that can cause an engine to run lean or rich-Refer to DTC P0171 or P0172 P0171.
* Incorrectly installed mass air flow (MAF)/intake air temperature (IAT) sensor.
* Incorrect crankshaft position sensor resistance-The crankshaft position sensor resistance may be out of range after a hot soak. The resistance should be between 700-1 200 ohms.
* 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 Knock Sensor Replacement Service and Repair and DTC P0324, P0326, or P06B6 P0324 and DTC P0325, P0327, or P0328 (LUW) P0325 and.
* Electromagnetic interference on the reference circuit can cause a misfire condition. You can usually detect electromagnetic interference 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.
* A leaking or restricted positive crankcase ventilation system
* A stuck open evaporative emission (EVAP) canister purge solenoid valve
* An incorrectly operating engine cooling system-Test or inspect for the following:
- A thermostat with an incorrect heat range-Refer to Thermostat Diagnosis (1.8L LUW and LWE) Thermostat DiagnosisThermostat Diagnosis (1.4L LUV) 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 (GE-47716 Fill) Cooling System Draining and Filling (GE-47716 Fill).
* Incorrectly operating or damaged exhaust system components-Test for the following:
- Physical damage or possible internal failure
- Restricted three way catalytic converters
For more information, refer to Symptoms - Engine Exhaust Symptoms - Engine Exhaust.
* An engine mechanical failure-Test for the following:
- Excessive oil in the combustion chamber or leaking valve seals
- Incorrect cylinder compression
- Sticking or leaking valves
- Worn camshaft lobes
- Incorrect valve timing
- 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
For 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.
* 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 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 panel cluster, however a DTC may not be set. Observe the scan tool Reduced Engine Power History parameter, if applicable, or refer to Engine Control Module Scan Tool Information 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 engine control module to reduce engine power-Refer to Cooling Fan Description and Operation Cooling Fan and Cooling System Description and Operation (1.4L LUV) Cooling System Description and OperationCooling System Description and Operation (1.8L LUW and LWE) Cooling System Description and Operation to verify correct operation of the cooling fan.
* Temporarily reduced engine power. Under extremely cold ambient temperatures some SIDI equipped vehicles may experience engine control module commanded reduced engine power for a few minutes during engine warm-up. This would be a normal condition, noticeable only at wide open throttle, and the reduced engine power lamp would not be illuminated.
* If the vehicle is equipped with the OnStar(R) feature, reduced engine power may be 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 OnStar Stolen Vehicle Slowdown Active and Remote Vehicle Speed Limiting Description and Operation Remote Vehicle Speed Limiting for additional information.
* Excessively high fuel pressure condition-Refer to Fuel System Diagnosis Fuel System Diagnosis and Fuel System Description Fuel System Description to verify fuel system operation.
* Maximum recommended engine oil life exceeded-Refer to the Owners Manual for scheduled maintenance recommendations.
* Intake air temperature out of range too high-Engine running, observe the scan tool IAT Sensor parameter. The readings should be between -40°C and +149°C (-40°F and +300°F). Refer to DTC P0112, P0113, or P0114 (LUW) P0112 for additional information.
* Fuel temperature out of range too high
* 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, the Brake Pedal Position Sensor Learn Brake Pedal Position Sensor Learn procedure must be performed.
Fuel Odor
* Inspect for a saturated EVAP canister. Refer to Evaporative Emission Control System Description Evaporative Emission Control System Description.
* Inspect for a condition with the internal components of the fuel tank assembly. Refer to Fuel System Description Fuel System Description.
Hard Start
* Observe the scan tool Throttle Body Idle Airflow Compensation parameter. 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 Inspection and Cleaning Procedures.
* Test the engine coolant temperature (ECT) sensor. Compare the ECT sensor value to the intake air temperature (IAT) sensor value on a cold engine. The ECT and IAT sensor values should be within approximately 3°C (5°F). If the ECT sensor is out of range with the IAT sensor, test the resistance of the ECT sensor. Refer to Temperature Versus Resistance (ECT) Temperature Versus Resistance (ECT) for resistance specifications. Replace the ECT sensor if the resistance is not within specification. If the sensor is within the specification, test the ECT circuits for a high resistance.
* Test the fuel pump relay operation. The fuel pump should turn ON for 2 s when the ignition is turned ON. Refer to Fuel Pump Electrical Circuit Diagnosis Fuel Pump Electrical Circuit Diagnosis.
Hesitation, Sag, Stumble
* Test the fuel pressure. Refer to Fuel System Diagnosis Fuel System Diagnosis.
* Test the manifold absolute pressure (MAP) sensor. Refer to DTC P0106 (LUW) P0106.
* Test the generator. Refer to Symptoms - Engine Electrical Symptoms - Engine Electrical. Repair the charging system if the generator output voltage is less than 9 V or more than 16 V.
Poor Fuel Economy
* Inspect for heavy loads being carried or towed.
* Inspect for acceleration rate too much or too often.
* Observe the scan tool Throttle Body Idle Airflow Compensation parameter. 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 Inspection and Cleaning Procedures.
* Inspect the brake system for brake drag.
Poor Fuel Fill Quality
* Inspect for restricted vent lines.
* Inspect for high fuel temperature.
* Inspect for a condition with the internal components of the fuel tank assembly
For more information, refer to the following:
* Evaporative Emission Control System Diagnosis Evaporative Emission Control System Diagnosis
* Engine Controls Schematics [1][2]Electrical Diagrams
* Fuel System Description Fuel System Description
* Evaporative Emission Control System Description Evaporative Emission Control System Description
Rough, Unstable, or Incorrect Idle and Stalling
* Observe the scan tool Throttle Body Idle Airflow Compensation parameter. 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 Inspection and Cleaning Procedures.
* Inspect the engine mounts. Refer to Engine Mount Inspection Testing and Inspection.
* Inspect the intake and exhaust manifolds for casting flash.
* An excessively high idle may be due to the floor mat interfering with the accelerator pedal. With this condition present, it may not be possible to shift the transmission into gear. Inspect the accelerator pedal for binding and verify that the floor mat is not interfering with the accelerator pedal movement.
Surges/Chuggles
* Verify that each injector harness is connected to the correct injector.
* Inspect for slow responding heated oxygen sensors (HO2S). 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 drivability condition. Refer to DTC P0133, P013A, P013B, P013E, P013F, P015A, P015B, P2270, or P2271 P0133 for additional information.