2005 avalanche Fog lights are staying on with

The fog lamps are computer controlled .the body control module (BCM) will energize the fog lamp relay control circuit. The BCM receives the park lamp ON signal from the interior park lamps supply voltage signal circuit.
DTC B2527 Front Fog Lamps Circuit Low
The body control module (BCM) monitors the front fog lamp switch signal circuit in order to determine when the fog lamp relay is to be energized. When the BCM senses that the front fog lamp switch signal circuit is grounded momentarily by pressing the fog lamp switch, the BCM energizes the fog lamp relay by grounding the fog lamp relay control circuit.

Your best bet , take it to the dealer . Could need BCM replaced , would need to do testing using the Tech 2 scan tool . A new BCM has to be programmed .

Body Control Module (BCM) Replacement
If the body control module (BCM) is replaced, the following procedures must be performed in the following order:
BCM Reprogramming--Refer to Body Control Module (BCM) Programming/RPO Configuration in Computer/Integrating Systems.
Important: This procedure has to be performed only for vehicles equipped with the Passlock™ System.
Theft Learn--Refer to Programming Theft Deterrent System Components in Theft Deterrent. A new BCM will learn the Passlock™ information automatically, but the powertrain control module (PCM) must still learn the theft information from the BCM.