Stuck in 4 Lo

[nickkendall]

I have a 99 tahoe and i recently replaced the transmission and transfer case it has auto 4 wheel drive it...it would not go into 4 high just 4 lo 2 high and 4 auto and yesterday i got it stuck in some snow and put it in 4 lo and now i am unable to get it out...The lights on the 4 wheel selector light up for about a second when i turn vehicle on and then they all go out..that is the only time i can get any light out of them and pushing buttons does nothing..i have it in shop melting off right now i wiggled the wires i could see and still have nothing...the service 4 wheel drive light has come on
from what i have heard i believe it is the 4 wheel selector switch or the actuator on the transfer case? is there a way i can tell? i really need to get it out of 4 lo so i can drive it so any help would be greatly appreciated
also would it be possible to remove actuator and shift it manually so i could drive it?
thanks much for any help

---------- Post added at 10:04 PM ---------- Previous post was at 08:11 PM ----------

or could it be the tccm? any help would b great

 

[scottg918514]

try putting the tc in neutral, by using the method listed in the manual.

 

[96ProCompTahoe]

it would be the transfer case actuator, not the front that controls the 4Lo function. wouldn't think the front acuator failure would cause the T-case to stay in low.

 

[SunlitComet]

the only two things that cause that to not shift out is the tccm or tcase shift motor. you could shift it manually but most likely the tccm will have to be disconnected and it will probably throw speed sensors and functions off but I can't be sure it won't leave the front axle locked since it is a motor as well. You would be back in 2hi though.

---------- Post added at 01:13 AM ---------- Previous post was at 01:10 AM ----------

Unfortunately the auto 4wd switched to trouble codes and you would need a scanner with gm enhanced functions to view them.

 

[dsump]

I totally agree with the above poster. Probably the most common is the Encoder motor. It will most likely NOT be the TCCM since it will shift already when you push the button. There is a way to set up a jumper wire on your scanner port to test for codes from the tccm, but you probably wont have any errors there. The encoder motor on the transfer case is probably the issue. But since you said you just the tranny and transfer case, do this first: Unplug all the connectors from the wire harness that go to the tranny and transfer case. Then spray each end of the plugs with electrical contact cleaner. Make sure you pull the transfer case fuse and or the battery. Then once the connectors are dry, plug in the connectors on the tranny and transfer case. Put your fuse back in, hook the battery back up and give it a try. I would do this before any other troubleshooting. If this doesn't work, come back here and we will get you fixed up. One step at a time.

 

[nickkendall]

first off thank you for all your help i really appreciate it!!!
today we undid all the plugs and messed with the wires and undid the battery
did this multiple times one time after we first hooked the battery up all the lights lit up and it showed that it was in 4lo and then it would not do anything but flash but it was in park at the time and the shifter was locked and would not let me shift to neutral to try and shift... after i turned it off and on again i was back to where they all flash for a moment and then all the lights are out and nothing brings them on...i got under it and removed the activator on the transfer case and manually shifted the transfer case i now have it out of 4 lo but after i turned it back now all i have is 2 wheel drive i can have high or low... this made no difference the lights still do the same flash and off...what i believe is the actuator on the front differential is not locked...so now what to do? i also took the transfer case switch out and opened it up and looked good and the connections did from what i could tell
does anyone have a diagram or a way to explain how this system works
i've been studying and reading up on it some there is a selector switch inside then there is computer that controls the transfer case and then the actuator on the transfer case so somewhere in there is my problem?
thanks again for all the help

 

[SunlitComet]

First, the 99 auto4wd are no longer decode by shorting terminals like the non-auto electric shifters. You need a qualified scanner which will give you the code on what is wrong specifically. If you have it in 2wd then leave it that way until you are sure what is going on. If your front actuator assembly was not working fully the TCCM would have tried to back out of 4wd after about 30 seconds. and not get stuck.

Here is some data but the error code would be best.

NVG 236/246-NP8 (Two Speed Automatic)


Transfer Case Shift Control Module
The transfer case shift control module uses the VIN information for calculations that are required for the different calibrations used based on axle ratio, transmission, tire size, and engine. The system does not know which calibration to use without this information.
The direct battery supply line (CKT 1640) provides the power to the module and motor circuitry.

Transfer Case Encoder Motor
The transfer case encoder motor consists of a permanent magnet (PM) DC motor and gear reduction assembly. It is located on the left hand side (drivers side) of the transfer case. When activated it turns the sector shaft of the transfer case (clockwise or counter clockwise) to shift the transfer case. The encoder motor is controlled with a Pulse Width Modulated (PWM) circuit within the transfer case shift control module. This circuit consists of a driver on both the Motor A and Motor B circuits. The encoder motor is bi-directional to allow the motor to shift the transfer case from 2HI or 4HI to neutral and 4LO positions.

Transfer Case Encoder
The encoder is mounted to the transfer case encoder motor assembly and is replaced as an assembly. The encoder converts the sector shaft position (representing a mode or range) into electrical signals inputs to the automatic transfer case control module. The module can detect what position the transfer case is in by monitoring the 4 encoder channels (P. A, B. and C). These inputs translates into AUTO, 2H 4H, Neutral, and 4L or in transition between gears.

Transfer Case Motor Lock
The transfer case motor lock is used to provide a 2H, 4H, and 4L lock-up feature. When the lock circuit is energized, the transfer case encoder motor is allowed to turn. When the transfer case is placed 2H, 4H, or 4L the motor lock circuit has no power provided to it and the lock is applied.
This assures that the transfer case remains in the current gear position. When AUTO is selected the motor lock remains applied until an adaptive mode (torque is applied to the front propshaft) is required. During an adaptive mode the motor lock circuit is energized and the motor lock is released, enabling the encoder motor to turn and apply torque to the front propshaft.

Transfer Case Speed Sensors
There are three speed sensors on the Automatic Transfer Case (ATC) , two on the rear output shaft and one on the front output shaft. Each speed sensor is a Permanent Magnet (PM) generator. The PM generator produces a pulsing AC voltage. The AC voltage level and number of pulses increases as speed increases.

Vehicle Speed Sensor
One of the two on the rear output shaft is the vehicle speed sensor (VSS) input to the powertrain control module (PCM). The PCM sends this information to the transfer case shift control module via the Class 2 Serial Data bus.

Rear Propshaft Speed Sensor
The automatic transfer case control module converts the pulsating AC voltage from the rear transfer case speed sensor to a rear propshaft speed in RPM to be used for calculations. The rear propshaft speed can be displayed with a scan tool.

Front Propshaft Speed Sensor
The transfer case shift control module converts the pulsating AC voltage from the front transfer case speed sensor to front propshaft speed in RPM to be used for calculations, and to monitor the difference between the front and rear sensor speed. It is also used in the AUTO (Adapt) mode of operation to determine the amount of slip and the percent of torque to apply to the front axle. The front propshaft speed can be displayed with a scan tool.

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 CKT 1567.

---------- Post added at 05:12 PM ---------- Previous post was at 05:02 PM ----------

BTW have you checked for any blown fuses yet?

 

[nickkendall]

thanks for the info
yes i have checked fuses and all were good
i talked to a mechanic and he said that there is no transfer case control module he said the encoder and motor that is on the case itself is the problem?
is that true no tccm?
from experience what would you suggest?
if i had it scanned would they be able to tell me exactly what part i need to replace? even though i already removed the actuator to shift out of 4 lo
could i test power going to the encoder motor somehow to see if it is getting correct power? how?

 

[SunlitComet]

There is a control module though the name might vary, it is right there on the diagram. The shift motor can be most likely the problem but I don't like throwing parts at it without knowing the cause. Find a better shop or tranny shop with the scanner ability or dealer at last resort to pull the service code. It will look like one of the below. And the sytem will have to be put back the way it was. Motor installed with whatever mode it was in and make sure you service light is still lit when testing to ensure you catch it. Do the best you can with driving it that way.

 

[SunlitComet]

Post the code and I will give you the related procedure.