09 GMC Envoy 4.2I, 171K mi. TC fluid changed about 30K mi ago. TC motor and axel disconnect replaced about 45K mi ago. Tried 4WD couple months ago when it was warm, worked normally. Tried a couple weeks ago when it was cold and slippery, did not work. Several days later, when it was warm, it worked. All lights on control light up on start up. Hear sound from axel disconnect. Either nothing from TC motor or slight grunt. After driving long enough for everything to warm up, if the car sits at idle or off for 10-15 minutes, 4WD will usually engage. Any ideas? Replace TC motor maybe?
SOLVED! 4WD doesn't like cold?
- Thread starter ts684
- Start date
I wonder if this is normal.. Mine used to do the same thing, but now I have a garage, and the problem stopped.
Mine will shift OK when cold or at least I can't remember a time that it failed. My shift motor is original and it does struggle a bit with some shifts.
Naturally I had to go check mine just now. It was 5° F this morning, now 11° F and mine sits out in the cold. It shifted many times just now, no complaints.
I would pull your shift motor and perhaps even open it up and check the grease?
Naturally I had to go check mine just now. It was 5° F this morning, now 11° F and mine sits out in the cold. It shifted many times just now, no complaints.
I would pull your shift motor and perhaps even open it up and check the grease?
There are multiple levels of reduction gearing, five I think, with a whole bunch of gears. One tooth was broken on one gear, looked like it just snapped off. If you didn't open the motor up you wouldn't know. 4WD would engage during the summer and when I tried in late fall on a warmer day. I would think the TC would warm up somewhat in driving but if it's cold outside not much if any heat gets to the TC motor until you're stopped. Is this reasonable? Last night it worked when I left the gym but after driving about 1/4 mile it stopped engaging. Admittedly, I kept turning the control knob thinking that the TC motor needed to be "exercized".
I too thought about exercising the shift motor.
Have you the capability of reading the TCCM codes? Even if there is no service light there can still be old codes/clues in there. Can be done with an inexpensive bluetooth elm327 clone obd2 adapter and the right smartphone app. It may yield something to look into.
Mooseman
Moderator
Did you have it on 4hi or on auto when it stopped engaging? What did it do when it stopped? Lights flash and turn off? The service 4x4 light come on?
We don't recommend using auto because it keeps the front wheels engaged when not needed, introducing extra wear and drag, and cycles the TC on and off, introducing wear on the encoder motor and the TC clutches. If you need 4x4, put it in 4hi. Don't need it, put it in 2hi.
I only go thru A4WD so I can hear the axel disconnect as a distinct sound, then to 4WD. When it doesn't engage, the light above 4WD will be flashing and eventually the service 4WD light will come on. This is going from 2WD, briefly thru A4WD, then stopping at 4WD.
I have the Veepeak? dongle and Torque Pro? I have used it to help with engine problems only, didn't know it could do much else.
I have the Veepeak? dongle and Torque Pro? I have used it to help with engine problems only, didn't know it could do much else.
Mooseman
Moderator
Oh yes it can. @TJBaker57 is our resident SME on it and should be able to guide you on how to pull the codes and possibly live data.
In the meanwhile, you could give the free Android app Chevrosys a try to get the code that the TCCM is giving for the problem, however, the service 4x4 light has to be on as I don't think it can show historical codes. I'm not sure if it can show TCCM codes though. There is also Car Gauge Pro but it's not free and is a bit clunky to use and hasn't been updated since 2015 but does scan all modules, including the TCCM. It also has to have the service 4x4 light on for the code to show.
In the meanwhile, you could give the free Android app Chevrosys a try to get the code that the TCCM is giving for the problem, however, the service 4x4 light has to be on as I don't think it can show historical codes. I'm not sure if it can show TCCM codes though. There is also Car Gauge Pro but it's not free and is a bit clunky to use and hasn't been updated since 2015 but does scan all modules, including the TCCM. It also has to have the service 4x4 light on for the code to show.
This afternoon , on the way to the garage I use, I tured onto some loose dirt and gravel. Gassing it in 2WD had the back end slewing around and the traction control light coming on. In 4WD, even with the light blinking, it took of better, nothing funny with the back end or traction control light. Can I be in 4WD but still have a blinking light? Something not quite making contact.? With right front wheel off the ground, I can't turn it with control in 4WD. So the disconnect is OK. Got a bit distracted and when I went to take the key out of the ignition I had a steady light. Turned control back and forth between 2WD and 4WD, everything seemed good. Until after I went in the house to clean up, come back, try again and have blinking lights.
Mooseman
Moderator
No, that's not normal. Once a mode is properly engaged, the light should be solid on the mode you selected. Sounds like an issue with the encoder motor but you said you replaced it. What brand was it?
The light should blink only while the TCCM is attempting to shift to the requested mode. After a successful shift the TCCM will keep the current mode indicator light on solid.
How is successful shift determined? Inside the shift motor, attached to the output shaft is a range position sensor. That sensor is also known as an encoder hence the oft heard name "encoder motor". This sensor is the sole means of the TCCM to determine where the shift motor is currently.
"A rotary encoder, also called a shaft encoder, is an electro-mechanical device that converts the angular position or motion of a shaft or axle to analog or digital output signals. There are two main types of rotary encoder: absolute and incremental. Wikipedia"
Looks like this...
There are 3 wires connected to the sensor, a low reference, a 5 volt source and a sensor return signal. Inside the sensor the 5 volt source is connected to a broken circle of resistive material where the other end of the resistive material is connected to the low reference. The remaining wire, the return signal is connected through to this resistive material by a set of wipers that rotate with the motor in such a way that the return voltage sensed varies with the position of the shift motor.
This is how the TCCM determines when a successful shift has occured. For a given mode position there is a small range of return signal voltage and the TCCM will rotate the shift motor until the sensed voltage falls within the acceptable range for the desired mode. Here I measure the return signal voltage with a 5 volt source, a range position sensor and a DMM...
My original sensor had a microscopic cracked solder joint in the sensor return terminal which resulted in intermittent operation.
With the light blinking at the 4Hi position the TCCM will be trying to turn the shift motor to that position. While rotating towards the 4Hi position one of the operational cams inside the transfer case will be applying forward propshaft clutch pressure. So even if you have not fully engaged 4Hi while that light is blinking you may very well be almost fully applied.
How is successful shift determined? Inside the shift motor, attached to the output shaft is a range position sensor. That sensor is also known as an encoder hence the oft heard name "encoder motor". This sensor is the sole means of the TCCM to determine where the shift motor is currently.
"A rotary encoder, also called a shaft encoder, is an electro-mechanical device that converts the angular position or motion of a shaft or axle to analog or digital output signals. There are two main types of rotary encoder: absolute and incremental. Wikipedia"
Looks like this...
There are 3 wires connected to the sensor, a low reference, a 5 volt source and a sensor return signal. Inside the sensor the 5 volt source is connected to a broken circle of resistive material where the other end of the resistive material is connected to the low reference. The remaining wire, the return signal is connected through to this resistive material by a set of wipers that rotate with the motor in such a way that the return voltage sensed varies with the position of the shift motor.
This is how the TCCM determines when a successful shift has occured. For a given mode position there is a small range of return signal voltage and the TCCM will rotate the shift motor until the sensed voltage falls within the acceptable range for the desired mode. Here I measure the return signal voltage with a 5 volt source, a range position sensor and a DMM...
My original sensor had a microscopic cracked solder joint in the sensor return terminal which resulted in intermittent operation.
With the light blinking at the 4Hi position the TCCM will be trying to turn the shift motor to that position. While rotating towards the 4Hi position one of the operational cams inside the transfer case will be applying forward propshaft clutch pressure. So even if you have not fully engaged 4Hi while that light is blinking you may very well be almost fully applied.
Replaced about 3 yr ago. Thinking no "name" brand. Not the cheapest but not the most expensive.
In a somewhat related answer, I have found this system to work quite well in the cold, hence I assume you have another mechanical or electrical issue causing it.
Mine has shifted just fine down to -40 ambient. I assumed at some point it should have difficulty but I have yet to find it. I followed the CAD rebuild thread and used M1 red #2 synthetic grease in it. Like most grease, especially a #2, this sht gets downright hard in those temps. I figured the CAD should be rendered inoperable at some point but no dice. It works as called upon.
Mine has shifted just fine down to -40 ambient. I assumed at some point it should have difficulty but I have yet to find it. I followed the CAD rebuild thread and used M1 red #2 synthetic grease in it. Like most grease, especially a #2, this sht gets downright hard in those temps. I figured the CAD should be rendered inoperable at some point but no dice. It works as called upon.
Due to my experience with both this 09 Envoy and a previous 04 Envoy, I felt reasonably sure that the TC motor was the problem. Having to drive through a winter storm tomorrow, helped me make the decision. Replaced TC motor, everything works for now. I will take a look at the old unit to see if I can find any problem
Mooseman
Moderator
That wouldn't have inspired a lot of confidence for me so yeah, seems to have fixed it for you. Maybe the grease they used in it wasn't the best in cold? If you can figure it out, it can become a spare.
What brand did you go with this time?
Dorman, only kind stocked locally. Did the job for 56mi return through 3-4 inches of slushy snow.
Mooseman
Moderator
. At least you got it working for now.