Hello all.. This is my first thread on here. Ill try to give a little back ground first.!

I recently mover from Ireland to TN, I bought myself the first decent looking automobile I found, Its a 2000, GMC Jimmy, just over 100,000 miles, it has a 4-button NV236 (NP8 in the glove box) type transfer case. I bought from a dealer knowing the 4WD was not working, the dealer reckoned the 4 button switch on the dash was faulty (Me knowing that dealers were know different to at home).! I done some research and saw a lot of problems with the vacuum lines, I went for a second look at the dealers and could clearly see the rotted vacuum lines running across the engine bay, so I took a chance and bought it.! I have done quite a bit of trouble shooting since, replaced all the vacuum lines, check a lot of wiring, connections, switches, buttons, and sensors since. Big thank you to swartlkk for posting the diagrams and information https://blazerforum.com/forum/tech-a...rmation-41198/

I have a few questions:

1. If there are fault codes present in the TCCM will the 4WD system work correctly once the problems are fixed? Or do they need to be cleared from the TCCM first?
2. When I measure resistance across the encoders DC motor I get a value of 20 ohms. Is this correct?
3. Any one recommend a good place to get the TCCM scanned in the Sevier county area?

Thank you very much for any help you can give.
Seanie

 

First, welcome.
1. I am not 100% sure, but if the problems are fixed the 4wd should work.
2. Have no idea if 20 ohms is good or not, motor winding resistance should be low, but ?
3. No idea on that one.

Now I know I have not provided you anything, hope to change that.

Describe the problem with the 4wd operation. Does the 4HI or 4LO light just flash when selected? Is there vacuum at actuator under the battery that engages the front axle? How about the cable at this actuator; does it move freely?

Have you checked the connector at the TCCM? Probably needs cleaning. I have found that the 4wd switch needs to be disassembled and solder joints re-flowed, especially the connector to get it working.

Again give us some details as to what happens when 4HI is selected.

 

I have checked out most of the common faults and ruled them out

• When I got home from the dealers I found both plugs to the TCCM disconnected
• I reconnected the TCCM and the LED's on the 4 Button switch started working again
• I replaced all vacuum lines, from the engine to the actuator underneath the battery
• I have one vacuum line blanked off where it should connect to the vacuum reservoir in the drives side fender
• The actuator under the battery moves correctly
• The cable between front diff and actuator moves freely
• The valve on fire wall works correctly
• The switch on the front diff works correctly
• The mechanical components inside the front diff work correctly and lock the front wheels
• All the fuses are good
• I checked every wire coming from or going to the TCCM
• The 4 button switch on the dash works correctly
• There is no corrosion on either of the two plugs connecting to the TCCM
• Encoder motor looks in good condition (It has a 4 pin and 6 pin connector)
• Both speed sensors in the transfer box work correctly

I am 100% sure my problem lies inside the TCCM or inside the encoder motor
I removed and disassembled the encoder motor

• I can turn the shaft on the transfer case and select 3/4 different positions by hand
• The brake on the motor works correctly
• The DC motor runs when powered
• The hall effect sensor gives out different singles when moved by hand (I am not sure how to interrupter these singles, but they do change the P, A, B and C channels between +5v and Gnd at different angles

When I turn the key
I can hear the motor break disengage
The DC motor trys to turn but struggles and is unable to move by the sound of it (It buzzes)
Relays click inside the TCCM
The 4wd Auto light flashes for approximately 60 seconds then
The 2Hi light flashes and either goes solid locking into 2Hi or
4Hi will flash and then lock in
The 4WD Service light does come on after approximately 5min idling or driving

To get to and from work I have the valve on the firewall disconnected thus not allowing it the lock the front diff, in this case if it does it lock onto 2Hi when it trys 4Hi it can not lock in and will just flash in 4Hi until the the next restart.

Pressing any button on the dash has no effect at all.

Thank you very much for any help you can give.
Sean

 

If the service 4WD comes on, there should be a code set that will help guide you. Unfortunately not many scanners read 4WD codes, except for the Tech 2 at the dealers. Car Gauge Pro will scan all faults and I know it will read BCM codes, but I have not verified that it will read/clear TCCM codes. You might want to try it if you have an Android phone. I recommend the BAFX Bluetooth OBD2 adapter as sold on Amazon. about $30 for both.

If you want to punt and try to save some money diagnosing just put an encoder motor in it first, and a TCCM too if that doesn't work. I agree that it has to be one or the other (or both). You can eat up a lot of money during diagnosis.