Air bag light

[Grandpappy]

A friend of mine has a '01 2500 CTD 5sp. When the truck is started up in the morning and after all the warning lights go through their test, the air bag light stays on and he gets a few sec. of bell alarm. The light stays on until the cab temp warms up and then clears. This just started with our "cold" weather here in S.E. Tx. The light will not stay on with starts later in the day, even with the cab same as outside temp, only after overnight starts. BTW..with the light on(when it should be off) every thing on the steering wheel works..horn,cruise and ect. but my guess is the air bags won't if needed. He didn't know how to check for codes but after I explained over the phone he will check and get back to me. Anyone have any ideas?

Thanks
Pappy