wont go into 4lo or hi just blinks

[proneck]

any ideas 2000 z71

[skipr]

Can you give alittle more detail? What is blinking? the turn signals, Are we talking about a electronic transfer case switch? Is that what is blinking? Did it work correctly before? ...etc.

[proneck]

the light on the switch blinks a few times and then goes off
it has worked fine previously

[skipr]

File In Section: 04 - Driveline Axle

Bulletin No.: 99-04-21-002

Date: April, 2001

TECHNICAL

Subject:
Four-Wheel Drive (4WD) Inoperative
(Replace Transfer Case Actuator/Shift Detent Plunger)

Models:
1999 Cadillac Escalade
1998-01 Chevrolet and GMC C/K Models (Tahoe, Denali, and Yukon)
with 4L60-E or 4L80-E Automatic Transmissions (RPOs M30, MT1)
and NV246 Transfer Case (RPO NP8)

Condition

Some owners may comment that the 4WD is inoperative.

Cause

This condition may be caused by an inoperative transfer case motor (actuator).

Correction

A new transfer case Teflon(R)-coated shift detent plunger (poppet) has been developed in order to correct this condition. This coating on the exterior surface of the poppet should reduce shift effort and wear. If you determine that the transfer case actuator is inoperative, replace the actuator and the poppet. Use the following procedure and the part numbers listed below.

1. Remove the transfer case actuator.

2. Install a new transfer case actuator, P/N 12474401.

3. Remove the transfer case oil drain plug. Drain the oil from the transfer case. Refer to the Transfer Case subsection in the appropriate Service Manual. If the plug is difficult to remove or stripped, refer to Corporate Bulletin Number 99-04-21-001.

4. Remove the plunger (poppet) screw. The poppet and the spring should come out with the screw.

Notice o not overtighten the poppet screw.

Overtightening may damage the screw.

Important : Verify that the 0-ring on the screw is not damaged. Replace a damaged 0-ring.

5. Install the new coated poppet, P/N 12474072 (coated blue), the spring, and the screw.

Tighten

[klinn]

Originally Posted by skipr

File In Section: 04 - Driveline Axle

Bulletin No.: 99-04-21-002

Date: April, 2001

TECHNICAL

Subject:
Four-Wheel Drive (4WD) Inoperative
(Replace Transfer Case Actuator/Shift Detent Plunger)

Models:
1999 Cadillac Escalade
1998-01 Chevrolet and GMC C/K Models (Tahoe, Denali, and Yukon)
with 4L60-E or 4L80-E Automatic Transmissions (RPOs M30, MT1)
and NV246 Transfer Case (RPO NP8)

Condition

Some owners may comment that the 4WD is inoperative.

Cause

This condition may be caused by an inoperative transfer case motor (actuator).

Correction

A new transfer case Teflon(R)-coated shift detent plunger (poppet) has been developed in order to correct this condition. This coating on the exterior surface of the poppet should reduce shift effort and wear. If you determine that the transfer case actuator is inoperative, replace the actuator and the poppet. Use the following procedure and the part numbers listed below.

1. Remove the transfer case actuator.

2. Install a new transfer case actuator, P/N 12474401.

3. Remove the transfer case oil drain plug. Drain the oil from the transfer case. Refer to the Transfer Case subsection in the appropriate Service Manual. If the plug is difficult to remove or stripped, refer to Corporate Bulletin Number 99-04-21-001.

4. Remove the plunger (poppet) screw. The poppet and the spring should come out with the screw.

Notice o not overtighten the poppet screw.

Overtightening may damage the screw.

Important : Verify that the 0-ring on the screw is not damaged. Replace a damaged 0-ring.

5. Install the new coated poppet, P/N 12474072 (coated blue), the spring, and the screw.

Tighten

Just so you are aware, that bulletin is for the older square front end silverado trucks (refered to as the GMT400 body line). In midyear 99 the rounded front end trucks came out (these are refered to as the GMT800 body line). The 2000 Z71 should be the GMT800 truck and that bulletin would not apply. I did find a bulletin for the transfer case module, but there are specific diagnostic trouble codes for the bulletin to apply. You need to have the transfer case module scanned for codes. If you can, post the DTCs when you get them, and I might be able to help further. The bulletin I found if for DTC B2725, and it states you should also have a "service 4wd" light on also. The ultimate fix for that is to replace the push button switch (transfer case shift control switch), but again only if the truck is acting exactly as the bulletin describes. It is really important to have the truck scanned for codes. Hope this helps.

[vnotaro]

Same thing happened to mine (2001 with the 5.3). Had the electronic transfer case switch on the dash replaced under warranty at about 15k-20k. Took care of the problem. Don't know if this will work for you but since you are probably out of warranty, it will be the cheapest thing to start with. Good luck.

[skipr]

Thats why I asked him to give more details. And there was no metion of "service 4wd". so how do you suppose there will be any codes when scanned? A blinking switch light is an indication of the actuator in transition, but in this case it is not able to complete the transistion so it defauts back to the 2wd setting. I thought since my 98 Z71 did the exact same thing, that this was a good place to start troubleshooting. I am quite aware of the bad switch TSB, but suggesting having scanned for codes is not (in my opinion ) good advice. Unless the VCM indicates there is a problem, no codes will be prsent. The VCM does not hide information.

[klinn]

Originally Posted by skipr

Thats why I asked him to give more details. And there was no metion of "service 4wd". so how do you suppose there will be any codes when scanned? A blinking switch light is an indication of the actuator in transition, but in this case it is not able to complete the transistion so it defauts back to the 2wd setting. I thought since my 98 Z71 did the exact same thing, that this was a good place to start troubleshooting. I am quite aware of the bad switch TSB, but suggesting having scanned for codes is not (in my opinion ) good advice. Unless the VCM indicates there is a problem, no codes will be prsent. The VCM does not hide information.

If you re-read my post, I was quoting a bulletin, not saying this is his problem or his fix. I searched bullitens, like you posted, but I was informing him the bulletin you posted was for the old GMT400 body style. The bulletin I was quoting is for the new GMT800 body style. I'm sure you know this, but bulletins are for common problems, that is the only, even remotely, related to his problem. Thats why my post stated "should also have a service 4wd light on". I know he didn't state he had that, thats why I put that there. The bulliten you quoted is for the auto-transmission vehicles with the NP8 transfer case. There were 5 transfer cases available in the 2000 model year (BW4401, BW4407, NVG-241-NP2, NVG-243-NP1, & NVG-246-NP8), also there was the auto transmission and the manual transmission available. Before you claim my bad advise, why did you post a bulletin for a specific vehicle with those options before finding out if it fit his truck? Never mind the fact the bulletin is only for 1998 & 1999 models. He did say it was a 2000. Do you think it might, just might be possible for that "service 4wd" indicator to be out? I was trying to save him from repalcing a switch and then saying it didn't fix the problem. The blinking light is an indication of a request for the transfer case to change, and the fact it doesn't is an indication of a malfunction. When a malfunction if discovered by a module, it records a DTC, usually. You stated, "it is not able to complete the transistion so it defauts back to the 2wd setting". When things are not able to complete transitions and go into default mode, they usually set codes. The whole reasons codes were designed, it to save time figuring out problems and repairing vehicles. If you would rather spend hours and hours scratching your head over a problem, go ahead. But after spending this many years in the auto industry, any manufacturer will tell you in the event of a problem, check to see if there are codes in the system that is acting up. Kinda utilizing the system created for this reason. The 2000 trucks use a transfer case control module, not the VCM (as you suggested). If there is a DTC set it will be found there, not in the VCM like you stated. Hmm, kinda sounds like you might need something to SEE if there are ANY codes in the transfer case control module. Unless you know another way to guarantee there is not a failure code without scanning, please let me know. If you want to tell me I am giving bad advise, go ahead, but at least know what you are talking about when you make a statement like that. Your 98 is a completely different truck than his 2000. These forums are for helping people, I DON'T HAVE TO HELP ANYONE, I CHOOSE TO BECAUSE I WANT TO. I work for a GM dealership and I know how much auto repairs cost. Dealerships are the last resort when you have a problem. I just thought I'd be the inside voice and help out someone with a problem. I am helping from the inside of a dealership, willing to use the resources only found at a dealership, to help someone who wants to diagnose and fix their vehicle without having to come through the front door and pay the price. I guess I'll have to rethink about replying to posts in the future, I certanly don't want to give bad advise. If you feel like I was giving bad advise, I apologize to you and proneck. I wish you the best of luck in your quest for the fix of your truck.

[skipr]

Ok we will do it your way. Go buy a $1,000 + scan tool and perform the following test. BTW I don't have to help anyone either but I have many times if you care to look at my past 545 post you will see that I have been very helpful to other members. You show up after 33 post and you own the place. With your advanced techinal jargon that isn't much good to a DIY'er. So here you go bro, lets confuse the hell out of this poor guy who just wanted a simple aproach to a common problem....

Transfer Case Shift Control Switch Indicator Flashes, then Returns to Previous Mode
Circuit Description

The transfer case motor is a bi-directional, permanent magnet, DC motor. When energized through motor control A or motor control B, the ground is provided by the opposing motor control circuit and then grounded through the transfer case shift control module ground circuit. The motor, through a series of gears, rotates a shaft which moves the mode and range forks to shift the transfer case between the ranges of 4HI, 2HI, Neutral (N) and 4LO.

If motor control A and B circuits are shorted together, or a motor control driver is damaged in the transfer case shift control module, the transfer case shift control module goes into a shift block mode. The transfer case module also goes into shift block mode if there is a mechanical concern, causing the shift lever detent shaft to bind, or if the transfer case shift control module is not seeing a signal from the Park/Neutral Position (PNP) switch. The shift block mode causes the mode indicator to flash for a period of time when another mode is selected. After that period of time has ended, the indicator reverts back to the previous mode selection.

Test Description
step 1: a: turn ign. on w/engine off
b: install scan tool
c: go ATC data list on tool and observe motor A & B current.
d: using the mode switch (instument panel) select different mode.

Does scan tool indicate amperage draw from the motor? If yes: go to Step 2
If No: go to step 6
Step 2: a:Turn ign off
b: Dissconnect transfer case shft control module and encoder motor.
c: With a DMM check if motor control A & motor control B are shorted together.

Did you find and correct problem? If yes: go to Step 9
If no: go to step 3

Step 3: a: Connect transfer case shift control module
b: with DMM check same as in Step 2-c

Does DMM indicate a resistence less than 100 ohms? If yes: go to step 7
if no: go to step 4

Step 4: Remove the encoder motor and check to see if shift lever detent shaft is binding.

Is it binding? if yes: go step 5
if no: go to step 8

Step 5: Remove transfer case and repair.

Did you complete repair? if yes: go to step 9

Step 6: Check instrument panel to see if correct transmisssion range is being displayed.

Is the correct range displayed? If yes: go to step 7
if no: do a sysatem dianogstic check

Step 7: Replace transfer case shift control module.

Did you complete repair? If yes: go to step 9

Step 8: Replace encoder motor.

Did you complete repair? if yes :go to step 9

Step 9: a: Use scan tool to clear DTC's.
b: Operate vechicle within conditions to allow for symtoms to occur.

Does symtoms still exist? if yes: go to step 1
if no: system ok


The numbers below refer to the step numbers on the diagnostic table.


1. This step helps to determine if the transfer case shift control module has the ability to command the encoder motor.
2. This step determines if motor control A and motor control B circuits being shorted together is causing a shift block.
3. This step determines if the motor control A and motor control B circuits are shorted together within the module.
4. This step determines if a binding shift lever detent shaft is causing a shift block.
5. This step has the transfer case removed and repaired.
6. This step determines if the PNP switch is sending the correct range signal.
7. This step replaces the transfer case shift control module.

[klinn]

Wow, didn't think that was the case. I don't own the place, don't want to own the place. Just trying to help. Looks like someone found the copy and paste button, trying to make it seem like we know so much. Technical jargon? The most elaborate word I used is switch. Sorry, don't know what to call it and make it not seem so confusing. At least I was trying to help, and not just post a bulletin that jumps right into a repair without diagnosing. Even in the bulletin you posted it states, "If you determine that the transfer case actuator is inoperative, replace the actuator and the poppet". I'll try not to be confusing here, but that is another way of stating diagnose. Ok then you want to talk about me giving bad advise, and get the vehicle scanned for codes which in it self is part of diagnosing? If that "diagnosing" word if confusing, I'll just call it "trying to figure out what is wrong". You can substitute that phrase where ever you find the term "diagnose". Look at the diagnose instructions you posted. I read "step 1b: install scan tool". Now I got to ask this, how do you plan to help diagnose if you need a scan tool, but it is bad advise to scan the transfer case module and see if there are codes? I don't have to spend the money for a scan tool, I own one. I can tell you the information and data they provide can save you tons of time, effort, and money. If this was not so, why do ALL manufactures have them? I guess this is a confusing concept. Depending on the problem, you might have to have the vehicle connected to a scan tool, instead of just making repairs because they fixed your truck, or your neighbors truck. I would call that guessing and not trying to figure out what is wrong with THIS truck. Not all problems can be fixed with a post forum. Sorry I brought it up.


You know what, this has gone too far, I'll be the bigger one and just bow out. Proneck, I hope you are able to fix your vehicle. Skipr, you just showed me the reason I do what I do, and just remember I'm that guy you will bring your car to when you get done scratching your head and you have spent alot of money guessing. Then you can pay again, because I'll use the right approach to diagnosing, oops that was confusing. I mean figuring out what went wrong. You own the place and you have the posts to prove it. I have no doubt you have helped people in your 545 posts, but apparently my measly 33 have done no good. I didn't know it took posts on automotive forums to prove my credentials. I think it has something to do with the fact that I have them in the first place. Sorry to step on your feet. You have the floor. I don't want any more to do with this discussion.

[pola367]

Our shop followed all the above and got the auto to shift in/out of 4 wheel. we replaced the transfer case/np8/4 wheel control brain. Auto was fine until customer drove for extend period. After shut down check 4-wheel light went out. Vehicle not here to pull codes, so I am out a little ahead of this. Any suggestions?

[Chuck D. Bones]

I have a similar problem.
1998 GMC Suburban 5.7L RPO NP8 - 114Kmi

LEDs do not light on 2Hi, auto 4WD, 4Hi or 4Lo. Sometimes neutral LED blinks. Appears to only run in 2Hi, occasionally "slips". "Service 4WD" does not light up (except during instrument panel self test when starting the vehicle).

This all started while on a trip to Santa Barbara. Took it to a tranny shop there, they read out the following error code, reset it and it did not recur for them: "CODE#U1026 loss of class 2 com w/auto/trans..." Either there were no transfer case error codes or they were unable to read them.

I have removed the transfer case motor/encoder. Is there a way to test this off of the vehicle? Will the motor run on DC? If so, how much current is required? Alternatively, can I hook the cables back up and run it with the motor not driving the transfer case shaft?

This thread indicates a weakness in the stock design. I plan on replacing the detent with the teflon coated part. Where is the detent screw located? Is it on the bottom of the transfer case next to the motor/encoder? Would like to know the motor/encoder is bad before replacing it. Or should I just replace it based on the age of the vehicle?

Thanks,

-- Chuck

[stick64]

Maybe our 99 Silverado Z71 problems are related to some of the above discussions ? How about if you are stuck in 4 Lo and will not go in to 4 Hi or 2 Hi when the buttons are pressed, would blink but not transfer to selection. Had to sit in neutral for a while and rev the rpms up then went in to 2 Hi. Reluctant to go back to 4 Lo anytime soon. Please offer any suggestions or advice.

[Chuck D. Bones]

First, in response to my own post, I believe I have fixed the problem. I was advised by Stickman on another thread to replace inst panel fuses 2, 24 & 4 in that order. Fuse #2 fixed the stuck xfer case problem. The fuse contacts were oxidized and probably had too much resistance.

Second, with regard to the 99 Z71, is the vehicle moving when shifting in or out of 4Lo? I have the bext luck engaging or disengaging 4Lo if the vehicle is in neutral and barely moving.

-- Chuck

[98Z]

I posted about this very same problem on my 98 Silverado, but it's been a while. I can see that I'm not the only one with this problem.

I just went out and checked the fuses and replaced them in the order stated... 2, 24, & 4. The contacts were a bit dirty, so I replaced with all new fuses. Still have nothing.

My switch lights come on at startup to let you know they work, but then they are all out. If I push 2HI nothing happens. If I push 4HI or 4LO nothing happens. If I put the truck in neutral and push 4HI, the lights on that switch blink and then the both stay on. If I push the 4LO, both lights blink, there is a clunk from the Tcase, and then the lights stay on. Then if I push 2HI, I get the clunk again and then the lights go off.

So I'm going to guess that my switches are fine, but something about the Tcase or the actuator are screwy... is this a good assumption?

I'd really like to be able to fix this myself. Local shops are killing me.

- Dave

P.S. - If it does sound like an actuator issue... is this the right item??
http://cgi.ebay.com/ebaymotors/ws/eB...9503205&rd=1,1