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 Instructionsprovides 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 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:

* Ensure that the engine control module (ECM) and malfunction indicator lamp (MIL) are operating correctly.
* 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 Programming and Relearning 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
* Ensure that the control module grounds are clean, tight, and correctly located.
* Ensure that the vacuum hoses are not split, kinked, and properly connected, as shown on the Vehicle Emission Control Information label.
* 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 the 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 Fuel System Diagnosis Fuel System Diagnosis.
- The fuel injectors for proper operation-Refer to Fuel Injector Diagnosis (With J39021 or Tech 2) Fuel Injector Diagnosis (With J39021 or Tech 2)Fuel Injector Diagnosis (With CH47976) Fuel Injector Diagnosis (With CH 47976).
- The fuel quality condition-Refer to Alcohol/Contaminants-in-Fuel Diagnosis Alcohol/Contaminants-in-Fuel Diagnosis.

* Test the ignition system for the following:

- Proper ignition system operation-Refer to Electronic Ignition System Diagnosis Electronic Ignition System Diagnosis.
- Spark plugs-Refer to Spark Plug Inspection Testing and Inspection.
- Spark plugs for correct application-Refer to Ignition System Specifications Application and ID.

* 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 Torque Converter Diagnosis.
- The proper operation of the A/C compressor
- Items that can cause an engine to run lean or rich-Refer to DTC P0171, P0172, P0174, or P0175 P0171.
- The crankshaft position sensor for proper operation
- The proper operation of the knock sensor system
- Inspect the exhaust system-Refer to Symptoms - Engine Exhaust Symptoms - Engine Exhaust.
- 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
- The proper operation of the evaporative emission (EVAP) canister purge solenoid
- The proper operation of the engine cooling system-Refer to Symptoms - Engine Cooling (2.4L) Symptoms - Engine Cooling.

* Inspect the engine for the following mechanical failures:

- 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
Refer to Symptoms - Engine Mechanical Symptoms - Engine Mechanical.

* If the above conditions do not address the symptom, refer to the additional symptoms tests.

Additional Symptoms Tests

Hard Start
* Observe the Throttle Body Idle Air Flow Compensation parameter with a scan tool. A value greater than 80 % may indicate an excessive accumulation of deposits in the throttle bore. Inspect the throttle body and clean, if necessary. Refer to Throttle Body Cleaning Procedures.
* Verify that the engine coolant temperature (ECT) has not shifted in value. Refer to Temperature Versus Resistance Temperature Versus Resistance.
* Verify the engine electrical system for correct operation. Refer to Symptoms - Engine Electrical Symptoms - Engine Electrical.
* Verify that the driver is using the correct starting procedure as described.
* Verify that there is adequate fuel.
* Inspect for excessive crankshaft endplay that will cause the crankshaft position sensor reluctor wheel to move out of alignment with the crankshaft position sensor.

Note: A vehicle with a camshaft actuator stuck in an unparked position may experience a hard start.

* Start and run the vehicle until fully warm. Observe the camshaft position variation parameter while accelerating up to 1,500 RPM and back to idle several times. The camshaft position variation should indicate a value for 1-2 s, then return to 0 degree. If the camshaft actuator does not respond, refer to Camshaft Position Actuator Cleaning and Inspection.

Hesitation, Sag, Stumble
* Inspect the mass air flow (MAF) sensor for obstruction, contamination, and damage. Refer to Throttle Body Assembly Replacement Removal and Replacement.
* 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.
* Inspect for excessive crankshaft endplay that will cause the crankshaft position sensor reluctor wheel to move out of alignment with the crankshaft position sensor.
* Test the manifold absolute pressure (MAP) sensor. Refer to DTC P0106 P0106.

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. Refer to Temperature Versus Resistance Temperature Versus Resistance.
* Inspect the mass air flow (MAF) sensor for obstruction, contamination, and damage. Refer to Throttle Body Assembly Replacement Removal and Replacement.
* Observe the Throttle Body Idle Air Flow Compensation parameter with a scan tool. A value greater than 80 % may indicate an excessive accumulation of deposits in the throttle bore. Inspect the throttle body and clean, if necessary. Refer to Throttle Body Cleaning Procedures.

Note: A vehicle with a camshaft actuator either stuck at full camshaft retard, in the Park position, or uncontrolled and wandering, may experience poor fuel economy.

* Start and run the vehicle until fully warm. Observe the camshaft position variation parameter while accelerating up to 1,500 RPM and back to idle several times. The camshaft position variation should indicate a value for 1-2 s, then return to 0 degree. If the camshaft actuator responds erratic, inconsistent, or not at all, refer to Camshaft Position Actuator Magnet Cleaning and Inspection

Detonaton/Spark Knock
* Test for an engine overheating condition.
* Verify that the engine coolant temperature (ECT) has not shifted in value. Refer to Temperature Versus Resistance Temperature Versus 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, Hesitation, or Cut Out
* Inspect the engine electrical system for correct operation. Refer to Symptoms - Engine Electrical 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 Throttle Body Assembly Replacement Removal and Replacement.

Note: A vehicle with a camshaft actuator stuck in the Park position may experience a lack of power during take-off.

* Start and run the vehicle until fully warm. Observe the camshaft position variation parameter while accelerating up to 1,500 RPM and back to idle several times. The camshaft position variation should indicate a value for 1-2 s, then return to 0 degree. If the camshaft actuator does not respond, refer to Camshaft Position Actuator Cleaning and Inspection.

Rough, Unstable, or Incorrect Idle and Stalling
* Observe the Throttle Body Idle Air Flow Compensation parameter with a scan tool. A value greater than 80 % may indicate an excessive accumulation of deposits in the throttle bore. Inspect the throttle body and clean, if necessary. Refer to Throttle Body Cleaning Procedures.
* Inspect the mass air flow (MAF) sensor for obstruction, contamination, and damage. Refer to Throttle Body Assembly Replacement Removal and Replacement.
* Inspect the engine mounts. Refer to Engine Mount Inspection Testing and Inspection.
* Inspect the intake and exhaust manifolds for casting flash.

Surges/Chuggles
* Inspect the mass air flow (MAF) sensor for obstruction, contamination, and damage. Refer to Throttle Body Assembly Replacement Removal and Replacement.
* Test the 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 and result in a high, but false, signal voltage, which gives a rich exhaust indication. The ECM reduces the amount of fuel delivered to the engine, causing a driveability condition.
* Verify that each injector harness is connected to the correct injector.

Note: A vehicle with a camshaft actuator uncontrolled and wandering may experience an engine surge.

* Start and run the vehicle until fully warm. Observe the camshaft position variation parameter while accelerating up to 1,500 RPM and back to idle several times. The camshaft position variation should indicate a value for 1-2 s, then return to 0 degree. If the camshaft actuator does not respond, refer to Camshaft Position Actuator Cleaning and Inspection 66. Camshaft Position Actuator Cleaning and Inspection and Camshaft Position Actuator Magnet Cleaning and Inspection 65. Camshaft Position Actuator Magnet Cleaning and Inspection.

Fuel Odor
* Saturated EVAP canister-Refer to Evaporative Emission Control System Description 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

Review the Reduced Engine Power Indication History parameter with a scan tool to determine the reason for the last reduced engine power event.