Symptoms - Engine Controls

 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.
 Symptoms Description

The symptom comprises conditions not covered by diagnostic trouble codes (DTC). Some conditions can cause several 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 gets 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 stalls.

 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

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:


• Ensure that the malfunction indicator lamp (MIL) is operating correctly. Use the scan tool to command the lamp ON and OFF.
• Ensure that there are no DTCs that are stored.
• Ensure 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 resistance in circuits or components. High resistance can be a resistance, irrespective of size, that disrupts the function of components.
• 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 Inspection

• Ensure that the control module grounds are clean, tight, and correctly located.
• Ensure that the vacuum hoses are not split or kinked, and are properly connected.
• Ensure that the air filter is clean and free from restrictions.
• Ensure 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, 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:
- The fuel system for correct operation volume and pressure-Refer to Fuel System Diagnosis.
- The fuel injectors for proper operation-Refer to Fuel Injector Solenoid Coil Test.
- The fuel quality condition-Refer to Alcohol/Contaminants-in-Fuel Diagnosis.
• Test ignition system for the following:
- Spark plugs for incorrect heat range or an abnormal condition-Refer to Spark Plug Inspection and Ignition System Specifications (LAU).
- For diagnosis of coolant or oil fouled spark plugs-Refer to Loss of Coolant or Oil Consumption Diagnosis.
- Wet down the secondary ignition system with water from a spray bottle-Wetting down the secondary ignition system may 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.
• Inspect for the following conditions:
- The proper operation of the transmission torque converter clutch (TCC) - The scan tool should indicate an engine speed drop when the TCC is commanded ON. Refer to Torque Converter Diagnosis.
- The proper 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 P2177 or P2187 or DTC P2178 or P2188.
- Slow responding heated oxygen sensors (HO2S). The HO2S should respond quickly to different throttle positions.
- Refer to Heated Oxygen and Oxygen Sensor Caution.

Water intrusion in the HO2S 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.


 Inspect the MAF sensor installation. A MAF sensor that is incorrectly installed may cause a hard start. Install the MAF in the proper direction. Refer to Mass Airflow Sensor Replacement.
- Inspect the mass air flow (MAF) sensor connections.
- Engine oil contaminated by fuel
- Vacuum hoses for splits or kinks-Verify that the routing and connections are correct.
- Knock sensor system for excessive spark retard activity-Observe the scan tool Knock Retard parameter for activity greater than 0°. Refer to Knock Sensor System Description and DTC P0326, P0327, P0328, P0331, P0332, or P0333 (LAU).
• The exhaust system components for the following:
- Physical damage or possible internal malfunction
- The three-way catalytic converters for a restriction

For more information, refer to Symptoms - Engine Exhaust.
• Electromagnetic interference (EMI) 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 EMI is present. Inspect the high voltage components near the ignition control circuit if a condition exists.
• The crankcase ventilation valve for proper operation-Refer to Crankcase Ventilation System Inspection/Diagnosis.
• Evaporative emission (EVAP) canister purge solenoid that is stuck open
• The engine cooling system for the following conditions:
- A thermostat with an incorrect heat range. Refer to Thermostat Diagnosis.
- Improper engine coolant level-If the level is low, refer to Loss of Coolant.
• The crankshaft position sensor for an intermittent condition-Observe the scan tool crankshaft position Resync parameter. The Resync 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.
• Inspect the engine for the following mechanical failures:

Refer to 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


Hard Start

• Inspect the throttle body and clean, if necessary. Refer to Throttle Body Inspection and Cleaning.
• 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 ± 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 - Engine Coolant Temperature Sensor for resistance specifications. Replace the ECT sensor if the resistance is not within specification. Refer to Engine Coolant Temperature Sensor Replacement. If the sensor is within the specification, test the ECT sensor circuits for high resistance.
• Check that the fuel system has sufficient pressure for engine start-up. See Diagnostics fuel system for fuel pressure specifications.
• Inspect for excessive crankshaft endplay that will cause the crankshaft position sensor reluctor wheel to move out of alignment with the crankshaft position sensor. Refer to Crankshaft and Bearing Cleaning and Inspection.

Hesitation, Sag, Stumble

• Test the fuel pressure. Refer to Fuel System Diagnosis.
• Inspect the mass air flow (MAF) sensor for obstruction, contamination, and damage. Refer to Mass Airflow Sensor Replacement.

• Test the generator. Refer to Symptoms - Engine Electrical. Repair the charging system if the generator output voltage is less than 9 V or more than 16 V.
• Inspect for excessive crankshaft endplay that will cause the crankshaft position sensor reluctor wheel to move out of alignment with the crankshaft position sensor. Refer to Crankshaft and Bearing Cleaning and Inspection.
•
Note

The following actions may need to be repeated in order to verify an intermittent intake or exhaust camshaft actuator condition.


 Engine warm and idling, verify the correct operation of the camshaft actuator system. Command the intake and exhaust camshaft actuator for each cylinder bank from 0 to 25 degrees and back to 0 while observing the appropriate scan tool Intake Camshaft Position Variance and Exhaust Camshaft Position Variance parameters. Each parameter should be less than 2 degrees in each of the commanded states.
• If any of the parameters is greater than 2 degrees, inspect the suspect camshaft actuator and camshaft actuator solenoid valve and valve bore for contamination, obstruction, and damage. Refer to the appropriate link below:
- Camshaft Position Actuator Solenoid Valve Solenoid Replacement - Bank 1 (Right Side) Intake

- Camshaft Position Actuator Solenoid Valve Solenoid Replacement - Bank 1 (Right Side) Exhaust

- Camshaft Position Actuator Solenoid Valve Solenoid Replacement - Bank 2 (Left Side) Intake

- Camshaft Position Actuator Solenoid Valve Solenoid Replacement - Bank 2 (Left Side) Exhaust

- Camshaft Actuator System Description



Poor Fuel Economy

• Heavy loads being carried or towed
• Acceleration rate too much or too often
• Inspect the brake system for brake drag.

• Inspect for incorrect operation of the speedometer.
• 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 (LCD, LBX or LBS) Engine Control Module Scan Tool Information (LBY) Engine Control Module Scan Tool Information (LHU) Engine Control Module Scan Tool Information (LLU) list. If the reading is not in the range specified in the list, test the resistance of the ECT sensor. Refer to Temperature Versus Resistance - Engine Coolant Temperature Sensor for resistance specifications. Replace the ECT sensor if the resistance is not within specification. Refer to Engine Coolant Temperature Sensor Replacement. If the sensor is within the specification, test the ECT sensor circuits for high resistance.
• Inspect the mass air flow (MAF) sensor for obstruction, contamination, and damage. Refer to Mass Airflow Sensor Replacement.
• Inspect the throttle body and clean, if necessary. Refer to Throttle Body Inspection and Cleaning.

Detonation/Spark Knock

• Inspect for excessive carbon buildup in the combustion chambers. Clean the chambers with Top Engine Cleaner. Follow the instructions on the can.
• Test for an engine overheating condition. Refer to Engine Overheating.
• 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 (LCD, LBX or LBS) Engine Control Module Scan Tool Information (LBY) Engine Control Module Scan Tool Information (LHU) Engine Control Module Scan Tool Information (LLU) list. If the reading is not in the range specified in the list, test the resistance of the ECT sensor. Refer to Temperature Versus Resistance - Engine Coolant Temperature Sensor for resistance specifications. Replace the ECT sensor if the resistance is not within specification. Refer to Engine Coolant Temperature Sensor Replacement. If the sensor is within the specification, test the ECT sensor circuits for high resistance.
• If there are no engine mechanical faults, fill the fuel tank with a known high quality fuel that meets the vehicle minimum octane requirements.

Lack of Power, Sluggishness, or Sponginess

• Ensure that the turbocharger air inlet and outlet ducts are tightly sealed and that the air passages are not obstructed. Inspect the turbocharger moving components for looseness, binding, wear, and damage. Refer to Turbocharger System Description and Turbocharger Cleaning and Inspection.
• Inspect the engine electrical system for correct operation. Refer to Symptoms - Engine Electrical.
• Verify that each injector harness is connected to the correct injector.
• Inspect the mass air flow (MAF) sensor for obstruction, contamination, and damage. Refer to Mass Airflow Sensor Replacement.



Rough, Unstable, or Incorrect Idle and Stalling

• Inspect the throttle body and clean, if necessary. Refer to Throttle Body Inspection and Cleaning.
• Inspect the mass air flow (MAF) sensor for obstruction, contamination, and damage. Refer to Mass Airflow Sensor Replacement.

• Inspect the engine mounts.
• Inspect the intake and exhaust manifolds for casting flash.
•
Note

The ECM uses the cylinder 1 intake camshaft position sensor to determine camshaft to crankshaft relationship in order to control fuel injector and ignition system synchronization. If the cylinder 1 intake camshaft position sensor signal to the ECM is intermittent, a stalling condition will occur and a DTC will not set.


 Inspect all cylinder 1 intake camshaft position sensor wiring for poor connections. Start the engine and check whether the engine stops when you move the harness to the intake camshaft position sensor for cylinder 1. Refer to Inducing Intermittent Failure Conditions for further diagnosis.

Surges/Chuggles

• Inspect the mass air flow (MAF) sensor for obstruction, contamination, and damage. Refer to Mass Airflow Sensor Replacement.

• Inspect for slow responding heated oxygen sensors (HO2S). The HO2S should respond quickly to a change in throttle position. If the HO2S 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 that results in a high – but false – signal voltage, which gives a rich exhaust indication. The PCM reduces the amount of fuel delivered to the engine, causing a driveability problem.
• Verify that each injector harness is connected to the correct injector.

Fuel Odor

• Saturated EVAP canister-Refer to Evaporative Emission Control System Description.
• A condition with the internal components of the fuel tank assembly-Refer to Fuel System Description.
• Inspect for damaged or deteriorated fuel lines.

ECM Commanded Reduced Engine Power

Refer to Engine Control Module Scan Tool Information (LCD, LBX or LBS) Engine Control Module Scan Tool Information (LBY) Engine Control Module Scan Tool Information (LHU) Engine Control Module Scan Tool Information (LLU) for various conditions that may cause reduced engine power.