Service 4wd light

I'm assuming your refering to a Chevy S10? There should be a small gear shift lever next to the standard gearshifter marked as 2HI, 4HI, Neutral, 4LO. This is your 2wd/4wd shifter. 2HI is for normal everyday driving as it is only powering 2 wheels for better MPG. 4HI is the same gearing as 2HI but powering all four wheels. This is your 'normal' 4WD setting. 4LO is a set of reduction gears designed for serious 'Off Road' conditions and should not be used on public highways. Your top speed will be Very low in this setting and the engine will be maxed out at full revs to get it.
DO NOT leave this lever in the Neutral position without the park brake ON. This setting completely disconnects the transmission from the wheels regardless of the gear you have selected so it will roll even if you select Park.

I guess you probably don't know what transfer case you have ?
SERVICE 4WD
Refer to
?€¢
Transfer Case Description and Operation in Transfer Case - NVG 149-NP3

?€¢
Transfer Case Description and Operation in Transfer Case - NVG 246-NP8

?€¢
Transfer Case Description and Operation in Transfer Case - NVG 261-NP2

?€¢
Transfer Case Description and Operation in Transfer Case - NVG 263-NP1

The NVG 246 EAU provides 5 modes, Auto 4WD, 4HI, 4LO, 2HI and Neutral.
The four manual mode, or range gear positions, of the NVG 261 transfer case are:
?€¢
2HI - 2 wheel drive high range

?€¢
4HI - 4 wheel drive high range, part-time

?€¢
4LO - 4 wheel drive low range, 2.72:1 gear ratio reduction

?€¢
N - Neutral, 4 wheel

The NVG 263 transfer case provides the driver with 4 manual mode/gear positions:
?€¢
2HI - 2 Wheel Drive high range

?€¢
4HI - 4 Wheel Drive high range

?€¢
4LO - 4 Wheel Drive low range

?€¢
Neutral

With the info I've given you ,you should be able too now !
There is probably a code stored somewhere !
DTC B0790 DTC B2725 DTC C0300 DTC C0305 DTC C0306 DTC C0321 DTC C0327 DTC C0359 DTC C0374 DTC C0379 DTC C0550.

THE TRANSFER CASE MOTOR IS ONLY FOR 4WD LOW. That would have never been the problem as soon as you confirmed it shifted into 4wd Low. 2wd and 4 Hi work off of vacuum. You may have one or two issues. A vacuum leak up by the front axle that engages the 4wd HI or the sensors on the transfer case.

You have to put the truck in neutral first then switch the 4hi and don't use the auto select. If it still won't switch you may have damaged the servo and need to replace it. Or worse damaged the transfer case. So try in neutral first and hope that works.

Okay the motor for the 4x4 got stuck in 4LOW, Can you accsess the 4x4 motor switch,at see if that will retract the motor and default to 2 wheel drive because the switch itself went bad and wont disengage. see if that will help if not youll just have to by pass the switch and trigger to its normal position make sure its in neutral also

can you hear the shifter motor trying 2 shift? if not its the shifter motor open the door and try 2 listen when your trying 2 shift it

Change shift solenoid

If they are blinking I believe it means that there are fault codes present in the pcm. You need to get the computer scaned to see if there are an codes present. If you live near an Autozone or Checker autoparts they can scan it for free.

your doing it right but your accuater is bad 59.00 auto zone easy install

Most common problem is the vacuum diaphragm that is so inconviently mounted UNDER the battery tray.The cable that locks in the front diff is attached to it and vacuum pulls it in/out.