This the procedure I followed to test and eventually remove my DRL module. This was originally posted by John (GM Master A.S.E Automotive technician) at "Just Answer". As always, I've added my comments in Red:
The daytime running lamps (DRL) will come ON when:
• The ignition is ON.
• The light is OFF.
• The parking brake is released.
When the exterior lights are ON, the DRL will turn OFF. To turn the DRL OFF when idling, apply the parking brake.
With everything plugged in ,apply the brake with the key on/engine off.The brake light in the dash should light & the headlamps should turn off.If not replace the DRL module.
Disconnect the negative battery cable.
Remove the instrument panel lower cover (i.e. the panel below the steering wheel column).
Reach underneath the instrument panel and remove the bolts and the daytime running lamp module (this is the black module labelled "Hamsar" - see picture below.
Disconnect the electrical connector.
Install new module in reverse order.