Cadillac 2011 DTS Owner's Manual page 155

If a floor mat is the wrong size or is not properly
installed, it can interfere with the accelerator pedal
and/or brake pedal. Interference with the pedals
can cause unintended acceleration and/or
increased stopping distance which can cause a
crash and injury. Make sure the floor mat does not
interfere with the accelerator or brake pedal.
Use the following guidelines for proper floor mat usage.
The original equipment floor mats were designed
for your vehicle. If the floor mats need replacing,
it is recommended that GM certified floor mats be
purchased. Non-GM floor mats may not fit properly
and may interfere with the accelerator or brake
pedal. Always check that the floor mats do not
interfere with the pedals.
Use the floor mat with the correct side up. Do not
turn it over.
Do not place anything on top of the driver side
floor mat.
Use only a single floor mat on the driver side.
Do not place one floor mat on top of another.
The driver side floor mat is held in place by two hooks.
3-53