Owners of 2004-06 Cadillac SRX, 2004-07 CTS and 2005-07 STS models with 2.8- or 3.6-liter engines may come into your store with a complaint that their fuel gauge reads empty even though there's plenty of gasoline remaining in the tank. GM says the inaccurate gauge reading may be accompanied by a "Fuel Level Low" message on the driver information center, and in some cases, an illuminated check engine light with trouble code P2066 in PCM memory.
One likely cause for the troubles is the PCM incorrectly relaying to the trip computer the actual amount of fuel being used, especially during short trips with frequent key cycles between tank fill-ups. Reprogramming the module with updated software is the only surefire remedy. Check with a dealer for the specifics of the flash.