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Having some trouble with '98 GMC Jimmy. The 4 HI light on the dash is on indicating that it is in 4 wheel drive, but it actually isn't. When the 2 wheel drive button is pressed, the light never comes on. The drive shaft from the transfer case to the front differential is turning, but I don't think the front hubs are locking in.

Is there a fuse somewhere that might be causing this? I checked the both fuse panels and all fuses are OK. Is it OK to drive like this with the 4 wheel drive light on or will this cause problems?
 

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first thing to make sure of is to check and make sure your hubs are not locking or else you will have problems wearing tires out and possably break some driveline components while turning on dry paved surfaces. It sounds as if the encoder motor is messed up and not switching the transfer case out of 4wd but i believe the hubs are not locked. but you will have to put the front up in the air and see if you can turn them or not to tell.
 

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I found this on another S-10 site. It says it's for a 94 but all the puch button t-cases are the 233 so it should be the same. This is just in case the problem is in the t-case. You could have no codes and the problem could still be in the front chunk, the cable, cacuum lines, or the vacuum actuator.

To read the codes for the 4wd on a 94 with electric shift t-case, install a jumper wire from terminals "J" and "A" on the ALDL (12 pin connector under the driver's side dash)
The lights on the 4wd indicator (switch) will flash in a pattern, there are only 4 codes, one flash is code one, 2 flashes is code 2, etc..
Code "1" is "Ram standby power" and is considered normal, may be caused by clearing the codes.
Code "2" is "Encoder fault"
Code "3" is "TCCM motor circuit"
Code "4" is "Ram/Rom failure"
If you have codes 2 or 3 check all the encoder motor connections at the t-case, if OK it will probably need a new encoder motor assembly.
If you have code 4, replace the TCCM.
To clear the codes, ignition off, pull the 5 amp TCCM fuse, wait at least 2.5 minutes, replace the fuse, then cycle the key on/off 5 times.
That's about it, a very basic system, just make sure all connections are good and no corrosion, and then it's either an encoder motor or TCCM.
 

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After looking at it further, the ATC fuse was blown in the fuse box under the hood. I am assuming that the ATC stands for actuator. Question is, this is the second time that this fuse has blown. It happens when it is being taken out of four wheel drive. Unfortunately I have not been in the vehicle when the driver has tried to shift it back into 2 wheel drive, so I don't know at what speed they are driving. If they shift out of 4 hi at a high speed, would it cause that fuse to blow???
 
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