GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2006 🢒 DTS 🢒 Vehicle Control Systems 🢒 Vehicle DTC Information 🢒 Poor Fuel Economy

Inspection/Test

Action

DEFINITION: Fuel economy, as measure by an actual road test is noticeably lower than expected. Also, economy is noticeably lower than it was on this vehicle at one time, as previously shown by an actual road test.

Preliminary
    • Discuss driving habits with the owner.
    • Inspect the following:
       - A/C operation
       - Correct tire pressures
       - Correct wheel and tire size
       - Excessive vehicle weight loads
       - Excessive acceleration

Sensor/System
    • Verify that the engine coolant temperature (ECT) sensor is not shifted in value. Refer to Temperature Versus Resistance .
    • Inspect the mass air flow (MAF) sensor for proper installation, obstruction, contamination, and damage. Refer to Mass Airflow Sensor/Intake Air Temperature Sensor Replacement .
    • Inspect the manifold absolute pressure (MAP) sensor for proper installation, obstruction, contamination, and damage. Refer to Manifold Absolute Pressure Sensor Replacement .
    • Inspect the MAF and MAP sensors for proper seating of the connectors and terminals.
    • Ensure the quality of the MAP sensor vacuum source.
    • Inspect for the proper operation of the exhaust gas recirculation (EGR) system. Refer to Exhaust Gas Recirculation (EGR) System Description .
    • Inspect for vacuum leaks and other unmetered air.
    • Inspect the crankshaft position (CKP) sensor for damage and proper installation. Refer to Crankshaft Position Sensor Replacement .
    • Monitor the knock sensor (KS) system for excessive spark retard activity.
    • Inspect for contaminated heated oxygen sensors (HO2S).

Fuel System
    •  Test the fuel system for correct operation, restriction, volume, and pressure. Refer to Fuel System Diagnosis .
    • Test for proper operation of the fuel injectors. Refer to Fuel Injector Diagnosis .
    • Test for fuel contamination. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
    • Inspect the throttle body for coking. Refer to Throttle Body Inspection and Cleaning .
    • Inspect for lean or rich conditions. Refer to DTC P0171, P0172, P0174 or P0175 Conditions for Running the DTC. Refer to DTC P0171 or P0172 or DTC P0174 or P0175 .

Ignition System
    • Inspect for proper ignition system operation. Refer to Electronic Ignition (EI) System Diagnosis .
    • Inspect the spark plugs. Refer to Spark Plug Inspection .
    • Inspect the spark plugs for correct application. Refer to Ignition System Specifications .
    • Inspect for damaged ignition coils within the ignition coil module assemblies.
    • Inspect for damaged or misaligned spark plug boots.
    • Inspect the CKP sensor for damage and proper installation. Refer to Crankshaft Position Sensor Replacement .
    • Inspect the CKP sensor and harness for electromagnetic interference (EMI).

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

Additional Inspections
    • Inspect for a restricted air intake system.
    • Inspect for a dirty or restricted air filter.
    • Inspect the engine mechanical for oil consumption, correct engine compression, and correct base engine timing. Refer to Symptoms - Engine Mechanical .
    • Inspect the engine electrical system for correct operation. Refer to Symptoms - Engine Electrical .
    • Inspect the engine cooling system. Refer to Symptoms - Engine Cooling .
    • Inspect the engine exhaust. Refer to Symptoms - Engine Exhaust .
    • Inspect the heating ventilation air conditioning (HVAC) system operation. Refer to Symptoms - HVAC Systems - Automatic and Air Conditioning (A/C) System Performance Test .
    • Inspect the transmission for proper shifting and torque convertor clutch (TCC) engagement. Refer to Symptoms - Automatic Transmission .
    • Inspect the brake system for drag. Refer to Symptoms - Hydraulic Brakes .
    • Inspect for proper operation of the speedometer.