GM Service Manual Online
For 1990-2009 cars only

Checks

Action

Definition: Fuel economy, as measured by actual road tests and several tanks of fuel, is noticeably lower than expected. Also, the economy is noticeably lower than it was on this vehicle at one time, as previously shown by actual road tests.

Preliminary Checks

    • Refer to Symptoms .
    • Check air cleaner filter for dirt or being plugged.
    • Visually (physically) check: vacuum hoses for splits, kinks, and proper connections.
    • Perform Powertrain On-Board Diagnostic System Check.
    • Check the driving habits of the owner.
    • Is the A/C ON full time (Defroster mode ON)?
    • Are the tires at the correct pressure?
    • Are excessively heavy loads being carried?
    • Is the acceleration too much, too often?
    • Suggest to the owner to fill the fuel tank and recheck the fuel economy.
    • Suggest to the driver to read the Important Facts on Fuel Economy in the Owner Manual.

Fuel System Checks

    • Check the fuel type and quality.
    • Check the fuel pressure. Refer to Fuel Supply System Check .

Cooling System Checks

    • Check the engine coolant level.
    • Check the engine thermostat for always being open or for the wrong heat range.

Additional Checks

    • Check the transmission shift pattern.
    • Check the torque converter Ccutch (TCC) operation. When the TCC is commanded ON, a scan tool should indicate an RPM drop.
    • Check the Service Bulletins for control module software updates.
    • Check for dragging brakes.