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.

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 be not be set.

Hard Start
- 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
- 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 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

* Verify the engine control module (ECM) and the malfunction indicator lamp (MIL) are operating correctly.
* Verify there are no DTCs stored.
* Verify the scan tool data is within the normal operating range.
* Verify there are no Bulletins available for the current symptom.
* Verify the vehicle tires are correctly inflated and meet original equipment specifications.

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 routed 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, 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 conditions:

- Incorrect operation, volume and pressure. Refer to Fuel System Diagnosis Fuel System Diagnosis.
- Leaking or improperly operating fuel injectors.
- Improper fuel quality. Refer to Alcohol/Contaminants-in-Fuel Diagnosis Alcohol/Contaminants-in-Fuel Diagnosis.

* Test the ignition system for the following conditions:

- Spark plugs for incorrect heat range, coolant or oil fouled, or an abnormal condition. Refer to Spark Plug Inspection Testing and Inspection and Spark Plug Replacement Service and Repair.
- Secondary ignition system component susceptible to moisture. Wet down the secondary ignition system with water from a spray bottle. This may help locate damaged or deteriorated ignition system components. Look/listen for arcing or misfiring as the water is applied.
- Weak spark. Use the EL 26792 - HEI Spark Tester for testing and refer to Electronic Ignition System Diagnosis Electronic Ignition System Diagnosis. For equivalent regional tools, refer to Special Tools (Diagnostic Tools) Special Tools (Diagnostic Tools).

* Test or inspect for the following conditions:

- Incorrect installation of the Mass Air Flow (MAF)/Intake Air Temperature (IAT) Sensor.
- Incorrect operation of the A/C compressor.
- Items that can cause an engine to run lean or rich. DTC P0171 or P0172 P0171.
- An intermittent crankshaft position sensor 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.
- Knock sensor system excessive spark retard activity. Observe the scan tool Knock Retard parameter for activity greater than 0° and refer to DTC P0324, P0326, or P06B6 P0324 for further diagnosis.
- Electromagnetic interference 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 leaking or restricted positive crankcase ventilation system.
- A stuck open Evaporative Emission (EVAP) Canister Purge Solenoid Valve.

* Inspect the exhaust system components for the following:

- Physical damage or possible internal malfunction.
- Restricted 3-way catalysts.
For more information, refer to Symptoms - Engine Exhaust Symptoms - Engine Exhaust

* Inspect the engine cooling system for the following conditions:

- A thermostat with incorrect heat range. Refer to Thermostat Diagnosis Thermostat Diagnosis.
- Improperly operating engine coolant thermostat heater. Refer to DTC P0597-P0599 P0597.
- Low engine coolant level. Refer to Cooling System Draining and Filling Cooling System Draining and Filling.

* Inspect the engine for the following mechanical failures:

- 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

* 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.

Poor Fuel Economy
- Observe the Throttle Body Idle Airflow 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 bore and clean, if necessary. Refer to Throttle Body Inspection and Cleaning Procedures.

Rough, Unstable, or Incorrect Idle and Stalling
- Inspect the engine mounts. Refer to Engine Mount Inspection Testing and Inspection.

Surges/Chuggles
- 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 room temperature vulcanizing 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.

Hard Start
* 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 Temperature Versus Resistance 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 operation. The fuel pump should turn ON for 2 s when the ignition is turned ON. Refer to 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 P0106.
* Test the generator system. Refer toCharging System Description and Operation Description and Operation ,Electrical Power Management Description and Operation Description and Operation for more information.

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 80 % 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.

Poor Fuel Fill Quality

Difficult to fill
* 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:

* Engine Controls Schematics [1][2]Electrical Diagrams
* Fuel System Description Fuel System Description
* Evaporative Emission Control System Description Evaporative Emission Control System Description

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 Fuel System Description.