99 Jimmy 4x4 no working properly


pitbull3825
02-04-2007, 06:39 PM
I Have changed every sensor and switch. I pulled the encoder motor off today and looked inside everything looks normal. If it is is the air everything seems to work normal. Take it out and drive it not working the switch says it is but its not. The relays and encoder do click and seem to work. I even borrowed a matco scanner and went in and watched the data as I drove it I noticed that the propshaft speeds and they are nowhere close and the rear tires spin and nothing from the front in 4 hi or 4 lo. What am I missing I really don't wanna take it to the dealer.

MT-2500
02-04-2007, 06:47 PM
I Have changed every sensor and switch. I pulled the encoder motor off today and looked inside everything looks normal. If it is is the air everything seems to work normal. Take it out and drive it not working the switch says it is but its not. The relays and encoder do click and seem to work. I even borrowed a matco scanner and went in and watched the data as I drove it I noticed that the propshaft speeds and they are nowhere close and the rear tires spin and nothing from the front in 4 hi or 4 lo. What am I missing I really don't wanna take it to the dealer.

What transfer case do you have?
Front axle locking in?
Have you checked for codes?
Fuses and wiring and vacuum to front axle shift switch under battery checked?
What propshaft speed are you checking with rear wheel speed?
Also run a search on 4W shift problems on here.

J-Mech
02-04-2007, 06:51 PM
The front axle has a lockout on it did you check that? What about the front halfshafts (cv joints)?

pitbull3825
02-04-2007, 07:12 PM
No codes on transfer or engine pcm. I have the 2 speed auto transfer. Checked fuses checked vacuum replaced the actuator under the battery. Yes I checked the front propshaft speed against the rear. I did check the front lock out also replaced the cable that pulls it in. HELP...

old_master
02-04-2007, 07:16 PM
IF you have a NV233 (3 button): This is a part time transfer case which means the front driveshaft should free wheel until the encoder/motor engages the transfer case output shaft and the front differential actuator simultaneously locks the front differential when 4HI is selected. If the driveshaft speeds are not equal, the encoder/motor has not engaged the transfer case output shaft AND the front differential is not locked.

J-Mech
02-04-2007, 07:19 PM
What about the halfshafts? Is a cv joint broken? Jack up all 4 tires and put it in gear. Does the front driveshaft turn? If it does, but the front tires dont, then the prob is in the front axle. (may still be electrical though) If the driveshaft doesnt turn, prob is in transfer case.

pitbull3825
02-04-2007, 07:20 PM
The scanner does tell me the front axle is locked. I do have the 3 button switch. Off the ground the encoder motor and the front axle seem to engage at the same time. Real problem HUH?

J-Mech
02-04-2007, 07:22 PM
Not yet. You need to verify the front axle is kicked in. Jack it up.

J-Mech
02-04-2007, 07:23 PM
If the scanner says it is, you are most likely dealing with a mechanical problem.

pitbull3825
02-04-2007, 07:24 PM
I work for a local towing company I had the entire vehicle in the air and physically felt the front tires to see if they were engauged.

pitbull3825
02-04-2007, 07:26 PM
In the air I could not stop the front propshaft. It seems to only not work under a load. Is that strange?

old_master
02-04-2007, 07:37 PM
In the air I could not stop the front propshaft. It seems to only not work under a load. Is that strange?

Strange but not impossible. It's possible the fork in the front differential is not operating correctly. The fork position switch is indicating the fork is the proper position to have locked the differential, but if the fork does not actually move the lock, the front differential will not lock in.

J-Mech
02-04-2007, 07:39 PM
When you "felt" the front tires what do you mean. If the vehicle was off it was not in 4wd. The vehicle needs to be running, in 4wd, and in park. The front diff will let one tire spin but not the other. If it is in park and in 4wd it should turn the opposite tire the opposite direction that you turn it. If the other tire does not turn, it is not in 4wd. You have to know for sure if the problem is in the front axle or in the transfer case.

pitbull3825
02-04-2007, 07:42 PM
But I can feel and hear it pull to actuate the axles in the air. You think that maybe it not pulling all the way when the truck is on the ground? I did check the fluid in front axle. It looked good .

pitbull3825
02-04-2007, 07:44 PM
It has no vacuum if it not running like you said. It does kick in like you explained when in park. I had a older jimmy it had a few problems with the 4x4 but not this strange.

J-Mech
02-04-2007, 07:50 PM
Do the front tires roll in 4wd When in the air?

MT-2500
02-04-2007, 07:53 PM
But I can feel and hear it pull to actuate the axles in the air. You think that maybe it not pulling all the way when the truck is on the ground? I did check the fluid in front axle. It looked good .

Is it a 233 or a 236 transfer case?
How may buttons on push button shift and does any say auto on it?
How are you checking the 4W is not working?

pitbull3825
02-04-2007, 08:27 PM
The jimmy were talking about is a 99 does that help anyone?

pitbull3825
02-04-2007, 08:31 PM
Yes the front tires do roll in the air. It does have auto on the dash button. I am in the alley across the street from my house in Wisconsin. It has plenty of ice trust me. thats how I am checking it.

J-Mech
02-04-2007, 08:41 PM
I'm sorry. Do the front tires roll in the air in gear in 4WD.

pitbull3825
02-04-2007, 08:44 PM
Yes

pitbull3825
02-04-2007, 08:44 PM
I sorry I knew what you was talking about.

J-Mech
02-04-2007, 09:11 PM
OK. On the buttons it does have 4wd mode not just a automatic setting right? Or is 2wd 4wd low and auto the choices?

pitbull3825
02-04-2007, 09:55 PM
Sorry lost my dsl every one out of ideas?

MT-2500
02-05-2007, 10:53 AM
The jimmy were talking about is a 99 does that help anyone?


Yes and no.
We need to know what transfer case you have.
How many buttons on the shift panel and what does the transfer case tag on back of case say. Like 236 or other.
If a 236 the torque to front axle controlled by the by the pcm.
Does the 4W work in low or 4W high range?
If anything is bad it should show a code on a good canner.
On drives haft speed have you check it in 4W low or 4W high?
Will the front axle engage or pull in 4W low or 4W high?

pitbull3825
02-13-2007, 10:09 PM
I looked up the codes in the glove box and found NP5 and NP8 I did jack up the front axle and with the vehicle in 4x4 in park and running I can spin both front tires at the same time in the same direction and the propshaft also spins?????

pitbull3825
02-13-2007, 10:10 PM
opps I was useing a matco determinator scanner and found no codes????

old_master
02-13-2007, 10:15 PM
NP8 is the transfer case code. It is a 2 speed case, but doesn't say what model. On the rear of the transfer case there is a small metal tag. On the tag it will tell the model number of the transfercase. Post it back here.

pitbull3825
02-13-2007, 10:27 PM
Ok it will take a few days the wife has to work late tomorrow and god only know how much more snow WI is goona get thanks.

pitbull3825
02-13-2007, 10:28 PM
What about the VIN# whould that help at all?

pitbull3825
02-14-2007, 08:55 PM
I have a New Process 236 transfer any help??????

pitbull3825
02-14-2007, 09:10 PM
it is a 236

MT-2500
02-14-2007, 10:19 PM
I have a New Process 236 transfer any help??????

If it is a 236 then you need to find a transmission /transfer case capable canner and get the codes.
Also a good capable scanner is capable of running some test on transfer case shifting and reading data.
Going down the road the front and rear axl shaft sspeed sensors should be reading the same in 4 wheel auto or 4 wheel drive mode.
Are they? Is the front axle locking in good?
Any service transfer case lights on?

pitbull3825
02-15-2007, 07:56 AM
The matco scanner I was useing did read the different speeds and they wern't the same. I found no codes on the engine , trans , or transfer. I did lift the front tires to see if they were locked in and they were. I could spin both tires the same way in the same direction and the prop shaft turned with the truck in park and running in 4x4 I am pretty shure I am looking at a encoder motor but I wanna be positive...

MT-2500
02-15-2007, 10:04 AM
The matco scanner I was useing did read the different speeds and they wern't the same. I found no codes on the engine , trans , or transfer. I did lift the front tires to see if they were locked in and they were. I could spin both tires the same way in the same direction and the prop shaft turned with the truck in park and running in 4x4 I am pretty shure I am looking at a encoder motor but I wanna be positive...

If it was the encoder motor it would have a code and would not be shifting to different ranges.
When it has a problem all shift modes are disabled or will lock in whatever gear it is in.
When you put it in 2W does the front axle unlock and does the encoder motor shift and 2w button light up?
When in 4W does the 4W wheel light come on and does the axle lock in?
Will it shift from 4W to 2W and back?
What kind of transfer case fluid does it have in it? Blue or red or has it turned black?

On the drive shaft speed sensors they need to be reading the same for proper 4W operation. If not That may be your problem.
It uses the speed sensors to switch power to and from front axle threw a electronic clutch in the transfer case.
To have 4W you will have to get them speed sensors working right or together.

Here is a little info on the 236.
The NV 236 transfer case is a high and low speed transfer case that uses variable torque to front axel as needed to eliminate wheel slippage on rear axel.
With the 236 being use on some but not all late model Blazer and Jimmy and Envoy.
Look at the tag on back of transfer case or for the 5 push button panel
The driver can select mode with a push button switch.
The have 4 different shift push buttons and 5 shift modes.
1 = 2 wheel
2 = All W drive /auto mode.
3 = 4 wheel high
4 = neutral position
5 = 4 wheel low
One a 236 the ATC/PCM controls all shifting from driver input from the dash push buttons shift control and pcm/vcm information that tells the shift motor what range to shift the transfer case into and also locks the front axel in threw a vacuum switch and vacuum controlled front axel actuator and cable.
If the button lights up and does not flash after pushing it everything is ok.
But if the button starts flashing or does not light up you have a problem.
If a shift problem a code is set in the PCM all shifting is disable until the problem is fixed

In 2-wheel drive mode is for normal driving.
In 2W mode there is no front axel lock in and no power to front axel.
4 Wheel auto mode is for automatic 4-wheel drive on variable road conditions.
In 4 wheel automatic mode the front axel is locked in but no power is sent to front axel unless rear wheel slippage is detected by the transmission control module [ATCM]
How it works in AUTO MODE.
The ATC module can engage power as needed to the front axel while moving.
When rear wheel slippage is detected threw speed sensors on front and rear drive shafts.
It applies a pulse with modulated signal to the transfer case clutch.
To keep both front and rear axels pulling even.
With no rear wheel slippage detected it puts the pulling power on rear axel and acts works as a 2W drive.
Traction control and auto 4W built together.
Also in auto when under 5 mph and gas pedal is put to the floor the atcm/pcm will transfer torque to front axel to keep rear wheel from spinning.



With 4 W low being a lower gear ration for more pulling power.
Any shifting in or out of 4 wheel low should on be made when the vehicle is stopped.

The neutral position is for towing your vehicle but always consult your owners manual first for towing instructions.
Never us neutral position unless towing because the vehicle will roll in park or in gear if left in neutral


If there is a problem with the system the service 4W light will come on and set a code for the problem.
First check the 4WD-ATC and Illumining and Crank fuses and wiring and plug in and vacuum to front axel actuator.
But for any other electrical repair on it.
You will need a full body/engine/transmission/and transfer case capable scanner to get codes and data and test the transfer case system.
Test on most of the system can be run with a good capable scanner
There is one B body code and the rest are C codes that a problem turns on check transfer case light and will point to the trouble.
So if you have a problem you will need to get the code no to point you in the right repair direction.

Service is very important on the 236-transfer case to keep it working good..
Consult owner’s manual for service mileage info.
The 236 require the new blue GM auto track fluid. GM no. 12378508 for service.
Also some shop manuals were miss printed saying to use dexron 111 fluid.

pitbull3825
02-15-2007, 10:14 PM
I will be changing the fluid tomorrow. There are no codes. I will let you all know if it helps thank you all.

pitbull3825
02-15-2007, 10:20 PM
I will be changing the fluid tomorrow. There are no codes. I will let you all know if it helps thank you all.

MT-2500
02-16-2007, 10:11 AM
I will be changing the fluid tomorrow. There are no codes. I will let you all know if it helps thank you all.

What kind of fluid is in it now?
Are you working on the speed sensor problem?

Jimmy58
02-16-2007, 03:47 PM
Hi Pitbull, I have your same setup. I am a little unclear of your explanation of the front end. The way I check mine for proper operation is to jack up JUST the front drivers side wheel. With the truck in park and 2 or 4 wheel drive ( engine off) That wheel shoud not spin. This will check the mechanical system through the transfer case. The front drivers side wheel will always be tied to the transfer case. If you can spin this wheel you have mechanical problems. If not procede to step two.
Lower the drivers side tire back on the ground and lift the front Passengers side tire. This tire should spin when in 2 wheel drive. Start the truck and put the truck into 4 wheel Hi. this tire shouldn't spin now. The vacuum actuator should shift the coupling between the left and right tires ( connecting them solidly). If the tire still spins the actuator,Encoder Motor, PCM, or the 2 speed sensors are holding it out. No matter what type of fluid you have in the transfer/Front differential the transfer should shift. The different fluid was ment to solve a vibration /slippage problem. Get back to us.
Forgot about the Vacuum solenoid on the fire wall. It should be directly above the Distributor . It has 2 vacuum lines, one from the manifold and the other runs to the Vacuum actuator. Make sure you have vacuum to the solenoid and when switched to 4 Hi You have vacuum through it.

johnnyrocks43110
12-30-2007, 11:13 AM
when i had a busted cv joint i was stumped like this. the tire would spin in the air but under load it would not. i overlooked it once but then finally got frustrated and had a helper hold the brake and rev it up while i went around listening, the noise gave it away...is this anything like your problem? just trying to help. i'm told the fork pads go bad also. good luck, isnt this site wonderful!

MT-2500
12-30-2007, 11:23 AM
when i had a busted cv joint i was stumped like this. the tire would spin in the air but under load it would not. i overlooked it once but then finally got frustrated and had a helper hold the brake and rev it up while i went around listening, the noise gave it away...is this anything like your problem? just trying to help. i'm told the fork pads go bad also. good luck, isnt this site wonderful!

THIS POST IS ALMOST A YEAR OLD.
Always check the date on a post before posting back to it.
MT

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