I am looking at buying a 2004 Chevrolet Silverado 2500 diesel. I am told the airbag light is on, the sales guy told me it is the sensor ? I asked for a price at the local Chevrolet garage, the parts guy said the light could be a number of more costly things. Any way I can check this, as I have said I have not bought the truck yet.

thank you in advance

A local Autozone can do a OBDII scan for free. That may help. They may need to use a scanner capable of scanning the Air bag system.

You can try Before you buy a used car, get the facts - Carfacts.com to see if the car was in an accident.

Airbags are costly to replace. It could have deployed in an accident and not replaced. Costly.

KeepItSimpleStupid

Thanks for the advice, I have looked at carfax, the truck is clean in all departments.
Taking the truck to an Autozone would be tricky, the Silverado does not have a plate.

OK, then take the scanner to it. They allow you to use one with a deposit, for free.

Good thinking, I will do that. Will any OBD II scanner be able to check the air bag light / sensor ?

Not necessarily. Call and ask. They typically have Actron scanners. Here is a blurb from Actron's website:

Actron®