The reason the light is flashing constantly is because the vehicle is sensing that four wheel drive(4WD) is not working. These 4WD systems use vacuum from the engine to engage/disengage to front axle. The vehicle probably has no vacuum going to the front axle, which would not allow the 4WD shift to complete, which would then leave the light on the dash flashing.
First thing to check is that the vacuum actuator on the firewall is working as it should.
It's trying to tell you to take it to a qualified GM repair shop . Do you know about DTC'S - diagnostic trouble codes ? DTC'S stored in the transfer case shift control module . Need a professional type scan tool to read these codes . You have a problem with the transfer case Encoder motor , prop shaft speed sensor , control module , or wiring etc.... Which of these does your vehicle have ?
Transfer Case - NVG 233-NP1 (Two Speed Selectable)
Transfer Case - NVG 236 (Two Speed Automatic)
Mode Shifts
The mode shifts are shifts from 2HI to 4HI and 4HI to 2HI. A mode shift can be accomplished in any gear position and at any vehicle speed. If the system is in 2HI, the driver can shift into 4HI merely by pressing the 4HI shift select button. The 4HI button will blink status whenever a 2HI or 4HI shift is initiated and will continue to blink until the TCCM completes the shift. After the shift into 4HI is accomplished, the 4HI status lamp remains lit to indicate that the system is in 4HI.
There is a difference between when the TCCM sends voltage signals in order to engage a four wheel drive shift and when the vehicle is truly in four wheel drive. The transfer case can be shifted into 4HI and the front axle may not be engaged.
The driver can shift from 4HI back to 2HI by pressing the 2HI shift select button. The 2HI shift select button blinks until the shift to 2HI is complete. The 2HI shift select button will remain on once the shift is mechanically complete.
The New Venture Gear NV233 is an electronic shift transfer, with the following three modes of operation, Two-wheel drive high range, Four-wheel drive high range, Four-wheel drive low range. The gear reduction for low range is provided by a planetary gear set. The floor-mounted shifter has been eliminated. A switch, located on the upper right side of the instrument panel, is used to select the operating range. The indicator lamps on the switch show the current mode of operation. When the four-wheel drive has been selected, the four-wheel drive indicator lamp on the switch is designed to turn on when the front axle has engaged.
There is a lot of information for these systems in the factory service info. system .
Transfer Case Control Module Description
The TCCM performs the following functions:
• Receives input signals
• Processes the signal information
• Develops output signals
• Sends the output signal in order to control the shifting of the transfer case
The TCCM receives input signals from the following sources:
• The transfer case shift select buttons
• The NSBU switch on the vehicles with automatic transmissions
• The clutch position switch on the vehicles with manual transmissions
• The vehicle sped sensor calibrator module
• The encoder/motor range and the mode feedback signals
• The diagnostic enable
• The front axle mechanical status signal
In order to ensure the electronic shift system is operating properly, the transfer case control module (TCCM) continually performs diagnostics checks on itself and other parts of the electronic shift system when the ignition switch is in the run position. The following are different types of system checks that the TCCM continually performs.
Your best bet mite be to take it to a qualified repair shop.
Diagnostic Trouble Code (DTC) Displaying
The transfer case shift control module is equipped with the ability to store diagnostic information, which is useful to a technician in the event of module, component or wiring failures. This information can be retrieved from the transfer case shift control module by way of flash codes, which are displayed on the three transfer case shift control switch buttons. These buttons are located on the instrument panel to the right of the steering wheel Before obtaining DTCs, perform the following transfer case control module (TCCM) Self-Test.
TCCM Self-Test
Observe the transfer case shift control switch indicators while turning the ignition switch to RUN. A properly operating system will flash all indicators and then will return to the current gear. If the system is operating normally, then proceed to Displaying Codes.
If the TCCM failed the Self-Test, then test the following circuits.
• Battery Positive Voltage (40 and 1640), and Ignition 3 Voltage for battery voltage
• Ground Circuit for ground
• Diagnostic enable circuit for an open or high resistance
• Transfer case shift control switch connector
If the above circuits are normal but the TCCM still fails the Self-Test, replace the TCCM. Refer to Transfer Case Shift Control Module Replacement .
DTC Displaying
Turn OFF the ignition for 10 seconds.
Connect PIN 13 on the data link cable (DLC) to a ground. The DLC is located in the cab under the instrument panel on the driver's side.
Turn ON the ignition, with the engine OFF.
Observe the transfer case shift control switch select buttons for flashing codes. Refer to Diagnostic Trouble Code (DTC) List .
Important: If the transfer case shift control switch buttons all blink only once and then stop, no fault codes are stored in the transfer case shift control module.
• When one DTC is stored in memory, that code will blink that number of times followed by a 3 second pause and then repeat.
• If more than one code is stored, the first code will blink, followed by a 3 second pause and then the second code will blink.
• This sequence will continue until PIN 13 on the DLC is no longer grounded.
• If the TCCM will not communicate the presence or absence of DTCs, test the above circuits in Self-Test Step 2. If the circuits are complete, then replace the TCCM. Refer to Transfer Case Shift Control Module Replacement .
The other 4X4 system is a totally different animal SERVICE indicator (4WD/AWD) Lamp
The SERVICE indicator (4WD/AWD) lamp is an integral part of the cluster and cannot be serviced separately. This lamp is used to inform the driver of the vehicle of malfunctions within the automatic transfer case (ATC) system. The SERVICE indicator (4WD/AWD) lamp is controlled by the transfer case shift control module via a Class 2 message or by a Sevice Indicator Control Circuit.
DTC C0367 Front Axle Control Circuit High
Circuit Description
The front axle control circuit consists of a Front Drive Axle Clutch solenoid which is electronically controlled by the transfer case shift control module. This solenoid opens and closes a vacuum control valve allowing vacuum to apply and release a clutch pack inside the front axle housing. The transfer case shift control module determines whether or not the clutch pack has been applied or released based on a signal form the front axle switch mounted on the front axle housing assembly. The front axle is normally locked or engaged during AUTO 4WD, 4WD HI, and 4WD LO modes. The front axle is unlocked or disengaged only during 2 HI or neutral modes.
Could be the encoder motor , could be a lot of thing's ,rather then listening to any one on here ,taking it to a qualified repair shop is the best thing for you to do.
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SOURCE: 4x4 will not engage,lights just blink,and you can here clicking
The 4x4 system has a controller,or computer,called the Body Control Module and there will be stored trouble codes.To work on a system that's electronically controlled,you have to get the codes from the system.Every trouble code has a diagnostic route to follow to resolve the faulty component.I have read about Explorers having faulty door open/closed sensors.These set a code in the Body Control Module,and in the process,the BCM inhibits 4x4 operation,causing a no 4 wheel drive complaint.There is also an electric motor on the transfer case that can fail electrically or mechanically,along with speed sensors and fork position sensors that can give trouble.
SOURCE: 2001 Dodge Durango stuck in 4 wheel-Low. Won't switch back to 2WD
Just to clarify, the "transmission" is not stuck in 4-Lo. It is the "transfer case" that is attached to the transmission that actually engages the 4-Hi and 4-Lo modes. To properly shift your vehicle into 4-Lo, you know that you have to shift the transmission into neutral and slow down to less than 5 mph. Once your vehicle slows down to this range, your can switch your transfer case into 4-Lo mode. Due to the inner workings of the transfer case, the actual shift into 4-Lo may take a few seconds to complete. This is normal and does not signify that there is an issue. All transfer cases that have 4-Lo mode will act this way regardless of the make or model. To make a long story short, to shift out of 4-Lo you must follow the same steps that you took to shift into 4-Lo, just in reverse order. Switch the transfer case to 4-Lo mode if it isn't already there. Slow down to less than 5 mph (your vehicle must be moving, though). Then, shift your car into 4-Hi or 2WD. Give your vehicle several seconds to complete the shift. The transfer case indicator light will flash until it is complete. When it does complete the shift into the new gear mode, you will most likely hear a "clunk" (the range sleeve inside the transfer case disengages from its mating spline) from under your car. Again, any transfer case with 4-Lo (regardless of make or model) will exhibit this same noise. This should help you get out of 4-Lo. It is good practice to shift your car into and out of 4-Lo at least a few times each year to keep all of the splines free of corrosion and build-up. Based on the age of your vehicle, your transfer case may also need a complete flush and some new transmission fluid. Hope this helps.
SOURCE: My 99 GMC Jimmy has the service 4X4 light on and
I own a Jimmy and have done quite a bit of 4 wheel drive repair on it.
The first thing i would check is the 4x4 selector switch. I know for a fact that these will throw a service 4x4 code if they are unplugged or shorted. They sell for 50-60$ or you may find one at a local salvage yard for cheaper.
Taking this out and checking it only takes a few seconds, just simply pop the switch out of the dash with the edge of your pocket knife.
After you get it out theres a few more tabs surrounding the back plate, and this is where the circuit board is located. I would inspect it visually to make sure nothing looks corroded and also take a sniff of it to insure there isn't a burnt smell.
If it were the 4x4 actuator the lights would still illuminate on the selector switch, it just wouldn't engage the 4x4.
You'r problem is all electrical trust me .
SOURCE: 4x4 push button is not working about how much does
This is something you can do yourself if you have ever worked on a vehicle before. The part you need is called a front drive actuator valve. It costs about $ 50.00, GM part # 15165891.
Here is some more infor about it:
Main 4wd Components:
TCCM - Transfer Case Control Module - Located behind the glove box. This is the electronic 'brains' behind the shifting.
Switch - The push button switch in the dash - driver input/indicator.
Encoder Motor - Located on the transfer case - This is what actually shifts the transfer case, and tells the TCCM what position it is in.
Vacuum Switch - Also located on the transfer case - This is what sends vacuum to the vacuum actuator (see below) when the transfer care is in 4HI or 4LO.
Vacuum Actuator - Located under the battery tray - This is what engages or disengages the front driveshaft.
Front Axle Switch - Located on the front axle - This is what tells the TCCM when the front axle is engaged.
If you want to try and replace it yourself, please let me know how it goes.
SOURCE: 2004 chevy silverado 1500 4 wheel drive wont work..
try selecting from nutreul or less then 3km
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