4wd problem

[Ryenol]

I have a 1998 K1500, seems that just in the past few weeks suddenly 4wd not working. Switch on dash just blinks, you can hear the transfer case engage, and the front drive shaft cannot be turned by hand. Front diff not locking in. I repacked dash switch to no avail, also had a new actuator that I plugged in and it doesn’t even move at all. PLEASE I need some help..

 

[RichLo]

I believe the 1998 has a vacuum controlled front driveshaft actuator. Check all of your vac lines for wear from rubbing or dry rot.

 

[Mark Gilbert]

98 is electric, at least the ones I have seen are.

You can disconnect the wire to the front actuator and then remove it. The whole assembly just unscrews from the case. Then reconnect the the wires and try and put the vehicle in 4wd. You should see the actuator extend, but it's only about an inch or so.

 

[Ryenol]

It is electric not vac. I have removed it and connected it and also connected a brand new actuator in the same manner but NOTHING!!!

 

[Mark Gilbert]

Sounds like you will have to trace some wiring.

http://lt1swap.com/1999_vortec_5.7/4WD, IAC, Upshift Controls.gif

This should apply to both the 98 and 99. I pulled it from www.LT1swap.com There might be more or better diagrams for you on there. Someone gave me a packet of info on this system, I will look for it and try and get it for you.

EDIT:

had more to add.

I would look at getting a scanner that can actually read Additional system codes. I was referred to Bluedriver and I really feel that for $100 it is a great tool. It will give you diagnostic codes for not just the PCM, but also the 4wd system, airbags, and ABS codes. (I wish it would let you cycle the ABS solenoids, but I guess you can't have it all for $100)

The CEL only has to illuminate when it is an emissions failure. Most cheap scanners won't be able to pull the extended codes.

https://www.motor.com/magazine-summary/transfer-case-studies-diagnosing-gms-4wd-system/

 

[Ryenol]

Thank you

 

[evilunclegrimace]

I believe the 1998 has a vacuum controlled front driveshaft actuator. Check all of your vac lines for wear from rubbing or dry rot.

The early S/T trucks had vacuum actuators The K trucks have always been electric

 

[evilunclegrimace]

It is electric not vac. I have removed it and connected it and also connected a brand new actuator in the same manner but NOTHING!!!

Before you go nuts Try swapping the t case switch out and see if the actuator engages.

 

[Ryenol]

Hoping to finish up re-looming wires tomorrow, went ahead and checked ALL the wires for breaks or anything bad.

 

[Ryenol]

Before you go nuts Try swapping the t case switch out and see if the actuator engages.

If it were the transfer case switch would unplugging that plug and jumping the wires on that plug cause the actuator to move? Or not necessarily?