GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2002 🢒 DeVille 🢒 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. Also, the fuel economy is noticeably lower than the fuel economy on this vehicle at one time, as previously shown by an actual road test.

Preliminary
    • Refer to Important Preliminary Checks Before Starting in Symptoms - Engine Controls .
    • Search for Bulletins.
    • Check the owners driving habits.
    • Check the following:
       - A/C operation
       - Correct tire pressures
       - Excessive vehicle weight loads
       - Excessive acceleration

Sensor/System
    • Check for an engine coolant temperature (ECT) sensor shifted in value. Refer to Temperature Versus Resistance .
    • Check the VSS system for proper operation. Refer to Powertrain On Board Diagnostic (OBD) System Check - Automatic Transmission in Automatic Transaxle.
    • Check the throttle body, throttle position (TP) sensor, and accelerator cables for proper operation.
    • Check the knock system (KS) for excessive spark retard.

Fuel System
    • Check the fuel pressure. Refer to Fuel System Diagnosis .
    • Check the fuel injectors. Refer to the following:
    • Check for fuel in the pressure regulator.
    • Check the minimum idle speed.
    • Check for items that cause the engine to run rich.

Ignition System
    • Check for proper IC circuit connections at each ignition module assembly.
    • Check for proper ignition voltage output using the J 26792 Spark Tester.
    • Check the ignition coils for cracks, or damage.
    • Check for a missing or damaged ignition module assembly grounding spring.
    • Check the spark plugs. Refer to Spark Plug Inspection .

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

Engine Mechanical
    • Check the following:
       - Engine compression. Refer to Engine Compression Test in Engine Mechanical.
       - Sticking or leaking valves
       - Worn camshaft lobes
       - Valve timing
       - Worn rocker arms
       - Broken or weak valve springs
       - Excessive oil in the combustion chamber-leaking valve seals
    • Check for incorrect basic engine parts. Inspect the following:
       - Camshafts
       - Cylinder heads
       - Pistons, etc.

Additional Checks
    • Check the exhaust system for possible restrictions.
    • Check the torque converter clutch for proper operation. Refer to Torque Converter Diagnosis in Automatic Transaxle.