1999 Chevy Silverado

[rockman20]

Hopefully someone here can answer my question even though it is a 99.

My girlfriend has a 99 Silverado 1500 extended cab short box. On the dash there is an information center and occasionally it tells her to service the 4WD. Now this light only comes on occasionally and has only been on like 3 times.

Does the transfer case on these pickups have a sensor in them to determine if the fluid is getting dirty? She has never had any fluids other then engine oil changed on this pickup.

I was thinking about changing the fluid anyways, but if this is a more serious matter, I would hate to change it just to have a service center dump it all anyways to rebuild or fix whatever is wrong with the 4WD.

Can anyone give me some ideas of where to look to see what exactly this pickup is complaining about?

Thanks!