Trailblazer stuck in 4LO??

[Nova63]

Hi guys,
I have an issue with my Trailblazer and would need some advice. The 4wd service light is on and the car seems to be stuck in 4LO. I have disconnected the ATCM fuse (number 8) and disconnected the battery without any luck. I also tried to rotate the selector switch back and forth for about 30 times.

I did a diagnose with my MD802 and it showed no fault codes except for in the specific code section that shows C0327 which indicate that there's something wrong with the transfer case encoder motor.

I'm trying to narrow this down, and see what you think;

4wd service light is on all the time
When turning on the ignition the four lamps above the selector switch blink one time, when start the engine they blink one time for about 1 or 2 seconds then went out. No lamp shows when turning the switch in neutral except for one time when both 2HI AND 4LO where constantly on at the same time. No clonking sound from under the car either.

Is there any way to see if the transfer case encoder motor is faulty with the diagnose check, if so how? What readings should I look for?

How would you continue to pinpoint the problem??

I guess its either the encoder motor or the TCCM or the wiring, but how to check it without replacing components??

Can you feed the Encoder motor solenoid with 12V and see if it works that way?

Thanks
Matt

 

[The_Roadie]

Welcome!

If you have a voltmeter, you can see if the encoder motor brake solenoid is being energized when you try to change modes. If it's not, then the encoder motor will be prevented from moving. You can also see if it's getting 12V on the motor terminals. To move the vehicle, you can always remove the encoder motor from the transfer case, and rotate the control shaft on the transfer case using pliers. Then you can see if the encoder motor moves while it's in the air. If it does, then you have a jammed transfer case.

Have you been changing the Auto-trak II fluid every 80K kilometers as required?

ALSO----> Can you confirm that you have the transmission in NEUTRAL, not PARK or DRIVE, while you try to get out of 4LO? You remember there's an interlock to prevent the TCCM from shifting if you're not in NEUTRAL?

 

[Nova63]

The_Roadie, thanks alot for your help!

I will start to work on the vehicle tomorrow or monday. If you want to set the car in 2HI manually when rotating the control shaft on the transfer case with pliers, which way should you turn the shaft?

Where can i found some info about the wiring between the switch-TCCM-Encoder Motor

Thanks alot for your help. appreciate it!

Matt

 

[The_Roadie]

The definitive Theory of Operation of the transfer case is on our sister site offroadtb.com:
http://www.offroadtb.com/articles/tech-docs/transfer-case-tech-the-nvg-226-np8-theory-of-operation/

Amazingly, I've never had my own encoder motor off to see how the manual shaft turns. Sorry. Don't forget to answer my other questions if you have time.

Here are the schematics.

 

[IllogicTC]

I've garnished what info I have on the manual shaft from the theory of operation, carefully studying the positions the shaft are in. Full counter-clockwise should be 4LO, so turning clockwise would bring you through neutral and into 2HI, then you'll hit the other "bump" where you get into A4WD/4HI territory.

 

[Nova63]

Thanks a bunch guys!

Sorry I didnt answer you Q before Roadie, was kinda in a hurry earlier today.

I know nothing about the oilchanges for this car, my friend just got it. But I get a feeling this issue is current related (TCCM, SWITCH, SOLENOID, or WIRING) in some way and not mechanical, just a feeling.

Yes, I had her in Neutral when trying to switch from Low to High, it was the same on my old 1977 Blazer with mechanical tranfer case selector.

Like I said thanks again, I will try to solve this issue, and now I have something to start with!

Matt

 

[Nova63]

One more thing, is the switch secured by clips so you just gently pry it lose from the dash or are there some hidden screws holding it in place? I was thinking maybe you could lose the contact and use a jumper wire and try it that way.

Matt

 

[The_Roadie]

You can pry the switch out from the front. But internally, it's a tapped resistor ladder. No way to replace it with a wire. Check the schematic.

 

[Nova63]

Ok, thanks for the info

Matt

 

[Nova63]

First, thanks for your help guys, it really helped!

I spent some time on the car today, and found out that if I wiggle the wiring harness going into the encoder motor at the same time as my buddy was in the car and turned the switch, the 4w warning lamp got away and the motor switched from 4LO to 2HI. We did some tests and we switched between the 4 modes and it worked when I wiggle the harness. The issue seemes to be just where the wiring going into the motor so I split the rubber boot so I could separate all 7 wires. It turned out to be the red one, probably 12V power that was bad contact inside the housing somewhere. I guess its close to the contact plate, so I will buy a new encoder motor.

I unbolted the motor and turned the axle with pliers to 2HI and went for a roadtest. Everything seems to work fine and now its driveable in HI gear. You think this will hurt anything if you drive it until the new motor arrives??? Ive sealed the contact and axle with tape to keep dirt and moisture out.

Where can I order a new complete Encoder motor for a decent price, any suggestions??

I'll attach a pic here: http://cubeupload.com/im/1yCyaZ.jpg

Thanks
Matt

 

[IllogicTC]

First, thanks for your help guys, it really helped!

I spent some time on the car today, and found out that if I wiggle the wiring harness going into the encoder motor at the same time as my buddy was in the car and turned the switch, the 4w warning lamp got away and the motor switched from 4LO to 2HI. We did some tests and we switched between the 4 modes and it worked when I wiggle the harness. The issue seemes to be just where the wiring going into the motor so I split the rubber boot so I could separate all 7 wires. It turned out to be the red one, probably 12V power that was bad contact inside the housing somewhere. I guess its close to the contact plate, so I will buy a new encoder motor.

I unbolted the motor and turned the axle with pliers to 2HI and went for a roadtest. Everything seems to work fine and now its driveable in HI gear. You think this will hurt anything if you drive it until the new motor arrives??? Ive sealed the contact and axle with tape to keep dirt and moisture out.

Where can I order a new complete Encoder motor for a decent price, any suggestions??

I'll attach a pic here: http://cubeupload.com/im/1yCyaZ.jpg

Thanks
Matt

Part number is 88996637. I'd search "GM 88996637," seems to turn up a bunch of relevant results on Google. eBay has them at a decent price (maybe $150-200). Parts dealers want between like $200-300.

Not sure on how well the Dorman unit works (plenty of other stuff the Dorman seems to be a temp fix), but if you're willing to do a little searching to check on how good it is or willing to swallow the potential for the fix being temporary, Dorman 600-903, $135 on Amazon. Apparently comes with a limited lifetime guarantee so if they keep pooping out you can just keep sending them back.

 

[Nova63]

IllogicTC, thanks!

I'll check that out. Im in Sweden, that make things a little more complicated, thats why I ask "1000" Questions to make sure I got everything right... Ya know, shipping, language etc etc,,, Better to ask twice And make it right the first time.

Thanks a bunch for your help!

Matt

 

[Nova63]

I found the Dorman 7 pin at Summit Racing for $166
A few bucks more but Ive been dealing with Summit many times and they are ok

Matt

 

[Nova63]

What do ya think guys, will it hurt anything using the car with the 7 pin contact to the encoder motor disconnected??

Matt

 

[The_Roadie]

You'll be fine.

 

[Nova63]

Thanks Roadie, appreciate your help!!! I will order the Dorman unit from Summit and hope for the best

Matt

 

[Nova63]

Roadie, you seem to know everything about these cars, can you look at the pic and tell if this is the New Process 226 Transfer case, RPO code NP8
I found the 7 pin

Dorman Transfer Case Motors 600-903
At summitracing, and just want to make sure I get the right part.

http://cubeupload.com/im/2xKma6.jpg

http://cubeupload.com/im/pBrHYl.jpg

Thanks
Matt

 

[The_Roadie]

I can't tell transfer cases apart by the appearance of the housing. Assume this is not YOUR vehicle? Just find out what sort of vehicle this is. Envoys and TB have NP226. Bravadas and Saabs have NP126. I always forget what the Isuzu and Buicks have, they're so rare.

 

[Nova63]

Its a 2002 TB, I didnt know everyone had the NP226. Thats why I asked.
Thanks
Matt

 

[05TB90TROOPER]

ALSO----> Can you confirm that you have the transmission in NEUTRAL, not PARK or DRIVE, while you try to get out of 4LO? You remember there's an interlock to prevent the TCCM from shifting if you're not in NEUTRAL?

TY Roadie, I had put it 4 lo yesterday after getting stuck in 4hi on a unplowed road with over 20" snow and higher drifts when I had to stop for a plow truck. The wife went out this morning and told me its stuck in 4lo. She tried everything except neutral.