Buick Regal: 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.
• Diagnostic Procedure Instructions provide 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 Tests. Perform the Symptoms Testing before using the Additional Symptoms Tests.

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 the malfunction indicator lamp (MIL) is operating correctly. Use the scan tool to command the lamp ON and OFF.
• Verify there are no DTCs that are stored.
• Verify 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 Check" described below. 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 the control module grounds are clean, tight, and correctly located.
• Verify the vacuum hoses are not split or kinked, and are properly connected.
• Verify the air filter is clean and free from restrictions.
• Verify there is no water intrusion in connectors terminals and components.
• Inspect the air intake ducts for the conditions listed below:
  • Collapsed
  • Damaged areas
  • Looseness
  • Incorrect installation
  • Leaking

    If any condition listed above has allowed non-metered air to enter the air induction system, the Throttle Body Idle Air Flow Compensation Reset procedure must be performed after the repair is complete.

• 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, Fuel Odor, Hard Start, Hesitation/Sag/Stumble, Lack of Power/Sluggishness/Sponginess, Poor Fuel Economy, Rough, Unstable, or Incorrect Idle and Stalling, or Surges/Chuggles

• Test/inspect the fuel system for the conditions listed below:
  • Incorrect system operation or fuel pressure - Refer to Fuel System Diagnosis.
  • leaking or incorrectly operating fuel injectors - Refer to Fuel Injector Diagnosis and Fuel Injector Circuit Diagnosis.
  • Contaminated or poor quality fuel - Refer to Alcohol/Contaminants-in-Fuel Diagnosis.
• Test/inspect the ignition system for the conditions listed below:
  • Spark plugs with incorrect heat range or an abnormal condition - Refer to Spark Plug Inspection and Ignition System Specifications.
  • Coolant or oil fouled spark plugs - For diagnosis, refer to Coolant in Combustion Chamber or 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.
• Test/inspect for the conditions listed below:
  • Non-metered air flow into the air induction system. If a leak is found, repair as necessary.

    The Throttle Body Idle Air Flow Compensation Reset procedure must be performed when the repair is complete.

  • Incorrectly operating transmission torque converter clutch (TCC) - The scan tool should indicate an engine speed drop when the TCC is commanded ON. For M3D or M3T, refer to Torque Converter Diagnosis (LTG) or Torque Converter Diagnosis (LGX). For MRC, refer to Torque Converter Diagnosis.
  • Incorrectly operating 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 for more information.
  • Slow responding heated oxygen sensors (HO2S) - The HO2S should respond quickly to different throttle positions - Refer to DTC P0137, P0138, P013A, P013B, P013E, P013F, P2270, or P2271 for more information.

CAUTION: 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.

• Incorrect mass air flow sensor installation. A mass air flow sensor that is incorrectly installed may cause a hard start. Install the mass air flow in the correct direction. Refer to Mass Airflow Sensor with Intake Air Temperature Sensor Replacement.
• Incorrect mass air flow sensor connections.
• A MAF sensor contaminated by an excessively oiled aftermarket air filter. Some aftermarket air filters require oil to be added to the air filter element. If the MAF sensor becomes contaminated as the result of an excessively oiled aftermarket air filter, a variety of driveability concerns and/or erratic transmission shifting may occur.
• Engine oil contaminated by fuel
• Split or kinked vacuum hoses - Verify that the routing and connections are correct.
• Excessive knock sensor system spark retard activity - Observe the Knock Retard parameter on the scan tool for activity more than 0º.
• 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.
• Incorrectly operating crankcase ventilation valve - Refer to Crankcase Ventilation System Inspection/Diagnosis.

• Test/inspect the engine cooling system for the conditions listed below:
  • A thermostat with incorrect heat range. Refer to Thermostat Diagnosis.
  • Incorrect engine coolant level - If the level is low, refer to Loss of Coolant.

    For additional information, refer to Symptoms - Engine Cooling.

• Test/inspect the exhaust system components for the conditions listed below:
  • Physical damage or possible internal failure.
  • Restricted three-way catalytic converters.

    For additional information, refer to Symptoms - Engine Exhaust.

• Test/inspect the engine for the mechanical conditions listed below:
  • 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, if necessary. Follow the instructions on the can.

    Incorrect engine parts

  • For additional information, refer to Symptoms - Engine Mechanical.
• 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 K20 Engine Control Module: Scan Tool Information , 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.

• Test for an engine overheating condition. Refer to 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.

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.

A repair may not be necessary. Observe the scan tool Reduced Engine Power History parameter, if applicable, or refer to K20 Engine Control Module: Scan Tool Information 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. 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 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 ECM 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.
• Reduced engine power due to OnStar remote command. Verify the vehicle is not in the OnStar initiated Stolen Vehicle Slowdown mode.
• Turbocharger boost pressure out of range, if equipped. Refer to DTC P0234 or P0299.
• High pressure fuel system condition. Refer to Fuel System Diagnosis and Fuel System Description to verify high pressure fuel system operation.
• Intake air temperature out of range too high. Observe the scan tool IAT Sensor 1 and IAT Sensor 2 parameters. The readings should be within 9ºC (16ºF) of a each other.
• Fuel temperature out of range too high. Observe the scan tool Fuel Temperature Sensor parameter.
• If equipped with automatic transmission, an incorrect learned brake pedal position (BPP) sensor.

  Verify the following actions have not occurred:

  • An engine control module has been replaced
  • A BPP sensor that has been replaced
  • An incorrect BPP sensor alignment or installation

    If any of the above actions occurred, the Brake Pedal Position Sensor Calibration must be performed:

Fuel Odor

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

Hard Start

• Observe the Throttle Body Idle Airflow Compensation parameter with a scan tool. A value greater than 90 % may indicate an excessive accumulation of deposits in the throttle bore. Inspect the throttle body and clean, if necessary. Refer to Throttle Body 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 ÂÂ+- 3ºC (5ºF). If the engine coolant temperature sensor is out of range with the intake air temperature sensor, test the resistance of the engine coolant temperature sensor. Refer to 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. If the sensor is within the specification, test the engine coolant temperature sensor circuits for high resistance.
• Verify that the fuel system has adequate pressure for engine start-up. The fuel pump should turn ON for 2 s when the ignition is turned ON. Refer to Fuel System Description and Fuel System Diagnosis.
• 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 and Engine Mechanical Specifications.

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 with Intake Air Temperature 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.
• Test the manifold absolute pressure (MAP) sensor. Refer to DTC P0106.
• 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 and Engine Mechanical Specifications.

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 actuators from 0 degrees to 20 degrees and back to zero while observing the 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 Camshaft Position Actuator Exhaust Solenoid Valve Replacement , Camshaft Position Actuator Intake Solenoid Valve Replacement , and Camshaft Actuator System Description.

Lack of Power, Sluggishness, or Sponginess

• Inspect the engine electrical system for incorrect 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 with Intake Air Temperature Sensor Replacement.
• Verify the correct operation of the turbocharger system. Perform the following:
  • Inspect the turbocharger moving components for looseness, binding, wear and damage.
  • Verify that the turbocharger air inlet ducts and outlet ducts are tightly sealed and that the air passages are not obstructed. Engine running, use a solution of dish soap and water in a spray bottle to pinpoint any air leaks.
  • Inspect the turbocharger system for external fluid leaks. Inspect the gaskets and sealing surfaces and look for cracks in the turbocharger components. Refer to Turbocharger Leaking Fluids Externally and Turbocharger Smoke or Smell.
  • Inspect for excessive turbocharger system noise. Refer to Turbocharger Noise.
  • Inspect for a loss of turbocharger pressure. Refer to Turbocharger Loss of Boost Pressure.
  • For additional information, refer to Turbocharger System Description and Camshaft Cover and Compressor Air Intake Turbocharger 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 actuators from 0 degrees to 20 degrees and back to zero while observing the 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 Camshaft Position Actuator Exhaust Solenoid Valve Replacement , Camshaft Position Actuator Intake Solenoid Valve Replacement , and Camshaft Actuator System Description.

Poor Fuel Economy

• Observe the Throttle Body Idle Airflow Compensation parameter with a scan tool. A value greater than 90 % may indicate an excessive accumulation of deposits in the throttle bore. Inspect the throttle body and clean, if necessary. Refer to Throttle Body Cleaning.
• Inspect for heavy loads being carried or towed
• Inspect for acceleration rate too much or too often
• 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 K20 Engine Control Module: Scan Tool Information , 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 , for resistance specifications. Replace the engine coolant temperature sensor if the resistance is not within specification. Refer to Engine Coolant Temperature Sensor Replacement. If the sensor is within the specification, test the engine coolant temperature sensor circuits for high resistance.
• Inspect the mass air flow (MAF) sensor for obstruction, contamination, and damage. Refer to Mass Airflow Sensor with Intake Air Temperature Sensor Replacement.
• Inspect the brake system for brake drag.

Rough, Unstable, or Incorrect Idle and Stalling

• 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.
• Engine idle speed may be unstable or the engine may stall if the ECM has learned an incorrect idle/airflow compensation value. A DTC may also set. 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. If the throttle body needs cleaning, refer to Throttle Body Cleaning.

The actions listed below may also cause the ECM to learn an incorrect idle value.

• The engine control module has been replaced
• The throttle body has been replaced
• The throttle body has been cleaned but the idle learn procedure was not performed after completing the cleaning
• The air induction system was leaking, allowing non-metered air to enter the combustion chamber. The leak was repaired but the idle learn procedure was not performed after repairing the leak

If any of the actions listed above have occurred, the Throttle Body Idle Air Flow Compensation Reset procedure must be performed.

• Inspect the mass air flow (MAF) sensor for obstruction, contamination, and damage. Refer to Mass Airflow Sensor with Intake Air Temperature Sensor Replacement.
• Inspect the engine mounts. Refer to Engine Mount Inspection.
• Inspect the intake and exhaust manifolds for casting flash.

Surges/Chuggles

• 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 with Intake Air Temperature 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 and result 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 condition. Refer to DTC P0137, P0138, P013A, P013B, P013E, P013F, P2270, or P2271 for more information.

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