GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2001 🢒 Sonoma Pickup - 2WD 🢒 Engine 🢒 Engine Electrical 🢒 Poor Fuel Economy

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DEFINITION: Fuel economy, as measured by an actual road test is noticeably lower than expected.

Preliminary
    • Refer to Symptoms - Engine Controls .
    • Search for service bulletins.
    • Inspect owners driving habits.
       - Is A/C ON full time, defroster mode ON?
       - Are tires at correct pressure?
       - Are excessively heavy loads being carried?
       - Is acceleration too much, too often?
       - Is E85 ethanol fuel used? If so, suggest the owner perform an actual fuel mileage comparison using standard unleaded fuel. If the fuel mileage is correct with standard unleaded fuel, the fuel consumption is normal.

Fuel System
    • Inspect the fuel pressure. Refer to Fuel System Diagnosis .
    • Inspect the fuel injectors. Refer to Fuel Injector Balance Test with Tech 2 .
    • Ensure each injector harness is connected to the correct injector/cylinder. Refer to Engine Controls Schematics .
    • Inspect items which can cause an engine to run rich--Short term FT significantly in the negative range. Refer to Diagnostic Aids for DTC P0172 .
    • Inspect items that can cause an engine to run lean--Short term FT significantly in the positive range. Refer to Diagnostic Aids for DTC P0171 .
    • Inspect for proper operation of the evaporative emission (EVAP) control system.

Sensor/System
    • Inspect the oxygen sensor (O2S 1). The O2S 1 should respond quickly to different throttle positions. If not, inspect the O2S 1 for silicon or other contaminants from fuel or the use of improper RTV sealant. The sensors may have a white powdery coating. Silicon contamination causes a high but false O2S 1 signal voltage--Rich exhaust indication. The powertrain control module (PCM) will reduce the amount of fuel delivered to the engine, causing a severe driveability problem.
    • Inspect for proper operation of the manifold absolute pressure (MAP) sensor.
    • Inspect for proper operation of the throttle position (TP) sensor.
    • Inspect for proper operation of the engine coolant temperature (ECT) sensor.

Ignition System
    • Inspect for proper ignition voltage output with a J 26792 Spark Tester or equivalent.
    • Inspect the spark plugs for the following conditions:
       - Wet or fuel fouled
       - Cracks
       - Wear
       - Improper spark plug gap
       - Burned electrodes or heavy deposits
    • If the spark plugs are fuel or oil fouled, the cause of the fouling must be determined before replacing the spark plugs.
    • Inspect the ignition control module (ICM) for proper ground connection.
    • Inspect the ignition coils for cracks or carbon tracking.
    • Inspect the spark plug wires for proper resistance and condition.

Engine Cooling System
    • Inspect engine coolant level for being low. Refer to Loss of Coolant in Engine Cooling.
    • Inspect for incorrect or malfunctioning engine thermostat. Refer to Thermostat Diagnosis in Engine Cooling.

Engine Mechanical
    • Inspect engine mechanical for the following:
       - Compression--Refer to Engine Compression Test in Engine Mechanical 2.2L (L43).
       - Sticking or leaking valves
       - Worn camshaft lobes
       - Valve timing
       - Bent push rods
       - Worn rocker arms
       - Broken valve springs
       - Excessive oil in combustion chamber-Leaking valve seals
    • For incorrect basic engine parts. Inspect for the following:
       - Camshaft
       - Cylinder heads
       - Pistons, etc.
    • Refer to Symptoms - Engine Mechanical in Engine Mechanical 2.2L (L43).

Additional Checks
    • Inspect the torque converter clutch (TCC) operation. Refer to Torque Converter Diagnosis in Automatic Transmission.
    • Inspect exhaust system for possible restriction. Inspect for the following:
       - Inspect exhaust system for damaged or collapsed pipes.
       - Inspect mufflers for heat distress or possible internal failure.
       - For possible plugged TWC--Refer to Restricted Exhaust in Engine Exhaust.