Part 1
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 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
Backfire
- The 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 occurs worse while under acceleration. The engine makes sharp metallic knocks that change with throttle opening.
Dieseling, Run-On
- The engine continues to run after the key is turned OFF, but runs very rough.
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.
Fuel Odor
- A noticeable smell of unburned fuel.
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 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.
* 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
* Test the fuel system for the following:
- Correct operation and pressure-Refer to Fuel System Diagnosis Fuel System Diagnosis.
- Improperly operating fuel injectors-Refer to Fuel Injector Solenoid Coil Test Fuel Injector Solenoid Coil Test.
- Improper fuel quality condition-Refer to Alcohol/Contaminants-in-Fuel Diagnosis Testing and Inspection.
* Test the ignition system for the following:
- Spark plugs with incorrect heat range or an abnormal condition-Refer to Spark Plug Inspection Testing and Inspection and Ignition System Specifications [1][2]Specifications.
- Coolant or oil fouled spark plugs-For diagnosis, refer to Coolant in Combustion Chamber Coolant in Combustion Chamber or Oil Consumption Diagnosis Oil Consumption Diagnosis.
- 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 J 26792 - spark tester-Refer to Electronic Ignition System Diagnosis Electronic Ignition (EI) System Diagnosis.
* Inspect for the following conditions:
- Improper operation of the transmission torque converter clutch (TCC) - The scan tool should indicate an engine speed drop when the TCC is commanded ON. For Non-Hybrid equipped vehicles, refer to Torque Converter Diagnosis Torque Converter Diagnosis.
- Improper operation of the A/C compressor
- An engine that runs lean or rich-Observe the Fuel Trim parameters with a scan tool. Refer to DTC P0171 or P0172 P0171.
- Slow responding heated oxygen sensors (HO2S). The heated oxygen sensors should respond quickly to different throttle positions. Refer to DTC P0133, P013A, P013B, P013E, P013F, P015A, P015B, P2270, or P2271 P0133 for additional information.
Caution: Refer to Heated Oxygen and Oxygen Sensor Caution Heated Oxygen and Oxygen Sensor Caution.
- Water intrusion in the heated oxygen sensors connector
Note: The embossed arrows on the mass air flow (MAF) sensor indicate the direction of the intake air flow. The arrows must point toward the engine.
- Improper MAF sensor installation. A mass air flow sensor that is improperly installed may cause a hard start. Install the mass air flow in the proper direction. Refer to Mass Airflow Sensor with Intake Air Temperature Sensor Replacement Service and Repair.
- Improper mass air flow (MAF) sensor connections.
- Engine oil contaminated by fuel
- 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-Observe the Knock Retard parameter on the scan tool for activity more than 0°.
* Electromagnetic interference (EMI) on the reference circuit, which 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 crankshaft position sensor with an intermittent condition-Observe the scan tool Crankshaft Position Resync Counter parameter. The Resync Counter parameter should remain at 0 during all operating conditions, and when moving the related harnesses and connectors between the crankshaft position sensor and the ECM.
* A stuck open evaporative emission (EVAP) canister purge solenoid.
* Improper operation of the crankcase ventilation valve-Refer to Crankcase Ventilation System Inspection/Diagnosis (Without Turbocharger) Testing and Inspection.
* The exhaust system components 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.
* The engine cooling system for the following conditions:
- A thermostat with incorrect heat range. Refer to Thermostat Diagnosis Thermostat Diagnosis.
- Improper engine coolant level-If the level is low, refer to Loss of Coolant Loss of Coolant.
* Inspect the engine for the following mechanical failures:
Refer to Symptoms - Engine Mechanical Symptoms - Engine Mechanical.
- Excessive oil in the combustion chamber or leaking valve seals
- Oil Consumption
- 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. Follow the instructions on the can.
- Incorrect engine parts
* If the above conditions do not address the symptom, refer to the additional symptoms tests.
Additional Symptoms Tests
Detonation/Spark Knock
* Verify that the engine coolant temperature (ECT) has not shifted in value. Allow the engine to run and reach operating temperature. Observe the ECT Sensor parameter with a scan tool and compare the reading to that parameter listed on the Engine Control Module Scan Tool Information (LUK) Scan Tool Testing and ProceduresEngine Control Module Scan Tool Information (LEA) Scan Tool Testing and ProceduresEngine Control Module Scan Tool Information (LHU) 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 (Engine Coolant Temperature Sensor) Temperature Versus Resistance (Engine Coolant Temperature Sensor) 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.
* Test for an engine overheating condition. Refer to Engine Overheating Engine Overheating.
* Inspect for excessive carbon buildup in the combustion chambers. Clean the chambers with Top Engine Cleaner, if necessary. Follow the instructions on the can.
* If there are no engine mechanical faults, fill the fuel tank with a known high quality fuel that meets the vehicle minimum octane requirements.
Engine Control Module (ECM) Commanded Reduced Engine Power (LUK)
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 (LUK) Scan Tool Testing and ProceduresEngine Control Module Scan Tool Information (LEA) Scan Tool Testing and ProceduresEngine Control Module Scan Tool Information (LHU) Scan Tool Testing and Procedures to determine the reason for the reduced engine power event.