99 blazer 4wd

I have a 1999 chevy blazer,the 4wd service soon light and all 4wd lights blink. It is a push button 4wd. The 4wd itself works fine also no codes come up. Any suggestions what could the problem be

Welcome on your first post.
Whick transfer case do you have?
Is it a push button with the auto mode or just regular 4W?

Not sure of transfer case but it is push button 4wd with auto 4wd

If the push buttons has the auto mode on it you will need good engine/transmission capable scanner to get the transfer case codes from it.
Just a OBD11 code check will not show transfer case codes.
Get the codes and post back code no. and someone will help.
MT

I have had this to the dealer 3 times no codes and they cant seem to find whats wrong they keep resetting computer hoping it will go away but hasn't yet

If the light is blinking there will be a code past or present in history.
I would consider another dealer or a good repair shop that has experiance on transfer case work.
First step on it is a good transfer case/transmission/engine capable scanner.

Tip on going to the dealer
Ask that only a factory certified gasoline engine and transfer case and transmissin performance specialist work on your car.
Not all dealerships are concerned with how repairs are dispatched, and not all dealership techs bother to take advantage of the training offered by factory (the vast majority of which is paid training). If the dealer is uncooperative, ask for your money back and call around for a dealer that will accommodate you.
MT

the dealer did check for codes on transfer case but no codes stored. i checked with a couple of other dealers and they said actuator or core motor .could this cause lights to blink? they dont blink in any sequence. sometimes only once or twice a day other times they go crazy .did it 6 times in 10 miles the other day .the day before only once.

the dealer did check for codes on transfer case but no codes stored. i checked with a couple of other dealers and they said actuator or core motor .could this cause lights to blink? they dont blink in any sequence. sometimes only once or twice a day other times they go crazy .did it 6 times in 10 miles the other day .the day before only once.


If the 4W is working good and shifting in and out of all 4W and 2 wheel modes I would not suspect the actuator/shift motor.
If the light blinks or is on the TCCM will have a code set in it.
Proper testing by a good tech should show the problem.
One thing to check real close is the speed sensors on the front and read drive shafts.
Is your tires and wheel matched up good.
Has the transfer case fluid been serviced with the new GM transfer case fluid?


The NV 236 transfer case is a high and low speed transfer case that is capable of using variable torque to front axle as needed to eliminate wheel slippage on rear axle.
Variable torque to front and rear axle is only used in the auto 4-wheel mode.
4-wheel high or 4-wheel low it acts as a regular full time transfer case.
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 4 push button panel for transfer case proper identification.
The driver can select mode with a push button switch.
The have 4 different shift push buttons and 5 shift modes.
Push buttons.
1 = 2W Drive.
2 = 4W Automatic.
3 = 4W High
4 = 4W low




Mode shifts
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 axle in threw a vacuum switch and vacuum controlled front axle 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.

The 2-wheel drive mode is for normal driving.
In 2W mode there is no front axle lock in and no power to front axle.
4 Wheel auto mode is for automatic 4-wheel drive on variable road conditions.
In 4 wheel automatic mode the front axle is locked in but no power is sent to front axle unless rear wheel slippage is detected by the transmission control module [ATCM]

How it works in AUTO MODE.
You can shift into 4-wheel auto mode at any speed under 75 mph.
The ATC module can engage power as needed to the front axle 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 encoder motor.
The encoder motor using a modulated signal from the TCCM and drive shaft speed sensors adjusts the variable torque pack to keep both front and rear axles pulling even.
With no rear wheel slippage detected it puts the pulling power on rear axle and acts works as a 2W drive.
Like Traction control and auto 4W as needed built in together.

The variable torque to front and rear axles is controlled by the encoder motor applying the proper position on the variable torque clutch pack.

Also in auto when under 5 mph and gas pedal is put to the floor the atcm/pcm will transfer torque to front axle to keep rear wheel from spinning.

4W high range the variable torque clutch is locked to full power to front and rear wheels.
This mode is made for driving conditions when you need extra traction and full 4-wheel drive all the time.
It should not be used on dry payment.
And any shifting into 4W high or 4W low should only be done when vehicle is stopped.
4 wheel low range is for when lower gear ratio is needed for more puling power.
And as in 4 wheel high the transfer case is locked into full power to front and rear axle.
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
Shift the transfer case to 2HI.
Simultaneously press and hold the 2HI and 4LO buttons for 10 seconds.
The red neutral light right under neutral will come on when the transfer case shift to neutral is complete.


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 axle actuator.
On the front axle vacuum actuator make sure it is pulling the cable to front axle lock in good.
The front axle vacuum actuator pictured below is located under the battery tray.
For any major electrical or mechanical 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.
Testing and shifting 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 well.
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.
MT