The switches control the ground circuit of the lock actuator motors. The common scenario is that the actuators get weaker after the first button press and then begin to do less on subsequent presses.....once you let them rest for a few minutes, you can repeat the process.
It's not hard to test, but the best way to do it is to actually measure current flow through the circuit. Measuring voltage will only test the switches, power, and ground circuits.
It's not uncommon for all of the actuators to take a dump (my 01 CC was the same way). One fails and the others slowly follow until none of them work.
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