2001 suburban service 4wd message light

I have a 2001 suburban 2500 that is 760 miles over waranty. I was driving it yesterday in 2wheel drive and it suddenly showed a service 4wd message on the message screen. This vechicle has used 4wd no more than about ten times and then only light duty, never any off roading. Can anyone tell me how to diagnose this? I know that the 2500 doesn't have an OBDll computer but does it use OBD1 and where is the access port. Can you jumper the contacts and get a read out or must a scanner be used? And finally, What does this message mean?

There has to be an OBD II (in use since 1996) on your truck. ODB I is history. Look under your dash board and you will find it. Do not short your connectors, you will kill your computer. You need a scanner or take it to the shop.

I have a 2001 suburban 2500 that is 760 miles over waranty. I was driving it yesterday in 2wheel drive and it suddenly showed a service 4wd message on the message screen. This vechicle has used 4wd no more than about ten times and then only light duty, never any off roading. Can anyone tell me how to diagnose this? I know that the 2500 doesn't have an OBDll computer but does it use OBD1 and where is the access port. Can you jumper the contacts and get a read out or must a scanner be used? And finally, What does this message mean?

Your truck has stored a code to aid with diagnostics that will have to be checked with a scan tool.
How you use your truck has no effect on the problem.
Most likely senerio is that the 4 wd switch on the dash is faulty and will need to be replaced. There is a GM tech bulletin about that issue.