i just yesterday purchased a 1999 gmc jimmy (i know it's not a blazer),anyway it has push button fourwheel drive.if i push the 4hi or 4 low button it goes into four wheel drive.i push the button 4xauto the service 4x4 light comes on.previous owner says bought this way,what is that button even for?the car had no manual to look it up any help would be appreciated thanks mike

 

i think that button for auto 4 wheel drive, so your car will be on 2wd for the most of the time but when you start sliding it will shift to 4wd automatically.

 

Thanks for info,guess it doesn't work on mine but I can push 4th or 4low and 4x4 works great

 

When you select 4HI or 4LO, the transfer case locks the front output clutch and delivers true 50/50 torque split F/R. The TCCM does not look at the speed sensor outputs to determine what position to put the clutch pack in.

The Auto4wd mode will engage the front axle, but leave the transfer case in 2wd. The NV236 transfer case is equiped with a clutch for the front output. It can vary the torque transmitted to the front axle depending on the slip detected by the speed sensors on the front and rear outputs of the transfer case.

As a wild guess, I would suspect that there is a problem with one of the speed sensor signals getting to the TCCM resulting from either a wiring problem or a problem with the speed sensor itself. Reading the TCCM codes requires a full feature scan tool capable of accessing serial bus connected devices. Since the 'Service 4wd' light is on, codes are stored and should be read before disconnecting anything. It will point you in the right direction!

 

question: Where would One obtain said full feature scan tool and for what price?

 

2000 chevrolet blazer ls pushbutton 4wd, 110K miles, lights flash on the switch or may go out all together, Service 4wd light comes on and then goes off, Vehicle is stuck in 4wd, The relays chatter on the tccm when the light are changing or flashing, Module is clean dry and free of corrosion,I can swith from 4hi to 4lo but seem to be unable to get back to 2 hi. Vac lines are in good shape no leaks found (I replaced a few pieces near the underhood light) is this apossible switch problem?

 

How many buttons do you have on the 4wd switch in the dash?