GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Buick 🢒 2005 🢒 Terraza - 4WD 🢒 Vehicle Control Systems 🢒 Vehicle DTC Information 🢒 Hesitation, Sag, Stumble

Inspection/Tests

Action

DEFINITION: Momentary lack of response as the accelerator is pushed down. Can occur at any vehicle speed. Usually more pronounced when first trying to make the vehicle move, as from a stop. May cause the engine to stall if severe enough.

Preliminary
    • Refer to Important Preliminary Inspections Before Beginning in Symptoms - Engine Controls .
    • Search for bulletins.
    • Inspect the powertrain control module (PCM) grounds for being clean, tight, and in the proper locations. Refer to Power and Grounding Component Views in Wiring Systems and Engine Controls Schematics .

Sensor/System
    • Inspect the air intake ducts for being collapsed, damaged, loose, improperly installed , or leaking especially between the mass air flow (MAF) sensor and the throttle body.
    • Test the exhaust gas recirculation (EGR) system for proper operation.
    • Inspect for proper operation of the manifold absolute pressure (MAP) sensor. Refer to Manifold Absolute Pressure Sensor Diagnosis .
    • Inspect for an engine coolant temperature (ECT) sensor that has shifted in value. Refer to Temperature Versus Resistance .
    • Inspect the MAF sensor and intake air system for proper operation.

Fuel System
    • Test for restricted fuel or incorrect fuel pressure. Refer to Fuel System Diagnosis .
    • Inspect for a contaminated fuel condition. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
    • Inspect for the following conditions that may cause the engine to run rich:
       - Water intrusion in the heated oxygen sensor (HO2S) connector
       - Engine oil contaminated by fuel
       - An evaporative emission (EVAP) canister purge condition
       - Leaking fuel injectors--Refer to Fuel System Diagnosis .
       - For proper operation of the MAP sensor--Refer to Manifold Absolute Pressure Sensor Diagnosis .
       - For proper operation of the MAF sensor. Refer to Scan Tool Data Definitions and Scan Tool Data List .
       - Vacuum hoses that are split, kinked, or improperly connected
       - An air intake duct that is collapsed or restricted
       - An air filter that is dirty or restricted.
    • Inspect for the following conditions that may cause the engine to run lean:
       - Water intrusion in the HO2S connector
       - An exhaust leak between the HO2S and the engine--Refer to Exhaust Leakage in Engine Exhaust.

Ignition System
    • Soak the secondary ignition system with water from a spray bottle. Soaking the secondary ignition system may help locate damaged or deteriorated components. Look and listen for arcing or misfiring as you apply water. Monitor the Misfire Current Counters while driving the vehicle in the conditions that the misfire occurred. If a misfiring cylinder can be located, use the DTC P0300 table for diagnosis. Refer to DTC P0300 .
    • Test for proper ignition voltage output with the J 26792 Spark Tester. Refer to Electronic Ignition (EI) System Diagnosis .
    • Remove the spark plugs and check for the following conditions:
       - Correct heat range
       - Wet plugs
       - Cracks
       - Wear
       - Improper gap
       - Burned electrodes
       - Heavy deposits
       - Refer to Spark Plug Inspection .
    • An improper spark plug gap will cause a driveability problem. Gap the spark plugs using a wire gage gap tool. Refer to Ignition System Specifications and Spark Plug Replacement .
    • Determine the cause of the fouling before replacing the spark plugs.
    • Inspect the spark plug wires for signs of arcing/cross firing, cracks, carbon tracking, plug boot damage, pinched, improper routing, or a resistance value outside the specified range.
    • Inspect for loose ignition coil grounds.

Engine Cooling System

Inspect the engine thermostat for proper operation and for correct heat range.

Engine Mechanical

Inspect for excessive crankshaft endplay that will cause the crankshaft position (CKP) sensor reluctor wheel to move out of alignment with the CKP sensor. Refer to Crankshaft and Bearing Cleaning and Inspection in Engine Mechanical. This could result in any of the following conditions:

    • A no start
    • A start and stall
    • Erratic performance