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2006 Chevrolet trailblazer EXT LT
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6 Posts
Discussion Starter #1
Hello all,

I recently purchased a trailblazer EXT LT and wanted to see how capable it was so I hit a local trail.i found that 4low would not engage. The light wouldn't even blink it anything. So here is what I have done below.

4 auto works no problem,
2hi works no issues,
4hi works no issues.
4lo I get nothing,
Neutral lock no issues

Put the TB In neutral move switch to 4lo at a stop. No flashing light nothing. Got the TB rolling and into neutral then 4lo left it there until the TB rolled to a stop nothing. Pressed stabilitrack button for 5+ seconds to turn of and attempted all steps above again. Still will not even attempt to go into 4lo. I verified the 4lo light is working ( when putting key in and turning all drive lights do show up.

Additionally I have also attempted to put the TB into 1st with the auto trans but it will only go into 2 and will not go into 1, but when driving I do get all the gears and it starts from 1st (not sure if this impacts the 4lo issue but thought it was worth noting)

Could this just be a bad 4x4 dash not going into 4lo or sensing I put it there?

Quick note this is my first 4x4 vehicle, I have always had and built sports cars but I have a big family now and this made more sense so I'm not familiar with the systems.
 

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2002 chevy trailblazer_lt
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174 Posts
If you never even get a flashing 4lo light I would look first at the selector switch. Some reccomend turning that switch back and forth with the key off in an attempt to clean the contacts inside. It sometimes works. I took mine apart and cleaned it out once.

IMG_20190321_150817.jpg
 

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2006 Chevrolet trailblazer EXT LT
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6 Posts
Discussion Starter #3
So today I opened the switch up and cleaned it out. I did find the connector that actually changes the selection was not on very good and made it fit better. Cleaned with alcohol and looks brand new. But still not working. All other options work and even Neutral. Next step get a switch from the salvage?
 

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2002 chevy trailblazer_lt
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174 Posts
Are you skilled with a digital multi meter? If yes, here's something to try.

The connection that carries the signal from the switch to the TCCM can be backprobed and checked with a meter. There should be specific voltages seen there. I have some pictures and video of doing the same thing for the encoder motor/transfer case position signal I will post & link here... It is the same procedure, just taps a different wire and the voltage readings are different. The colors given are for my 2002 trailblazer. It may be wise to verify colors for other years.

To monitor the selector switch, read the voltage on the light blue wire seen just below the brown/white wire being backprobed in my picture. The brown/white wire reports the encoder motor/transfer case position.

I don't have my voltage charts with me right now. I will update this evening with that information and maybe even a video clip doing the switch test.




IMG_20200422_180121.jpg
IMG_20200422_180020.jpg
IMG_20200422_175002.jpg
 

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2006 Chevrolet trailblazer EXT LT
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6 Posts
Discussion Starter #5
I'll have to find what you are talking about there. I was able to verify the switch is working. Basically I opened it up put the multimeter to the long connector then moved it to each of the others and verified I am getting 4.9v on all of them. Them after putting back together I was able to get to the pins and through process of elimination identify the out for each selection and found I am getting good out voltage on all options. I was going to attempt to test at the actuator but you can't test it with it connected. But it leads me to believe it's the actuator at this point.

As an additional note I resolved the issue not going into 1st with the shifter and adjusted the shift cable
 

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2002 chevy trailblazer_lt
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found I am getting good out voltage on all options.

There is only one 'out' voltage, all the others are the reference voltage of a nominal 5 volts having been dropped by various resistors within the switch. It is the specific value of this dropped voltage on the brown/white wire that tells the TCCM what position the selector switch is in. The voltage returned on that brown/white wire needs to be steady at approximately one of these following voltages.

2HI = 4.06
A4WD = 3.22
4HI = 2.42
4LO = 1.59
Neutral = 0.86

These values above are not from some specification but are the averages of my observations on both my own and others vehicles of this same platform.

When the TCCM sees a change of selector switch position by way of this returned voltage it initiates a shift, flashing the indicator light at the desired mode while sending the appropriate power to the transfer case shift motor to move to the desired position. Inside the transfer case shift motor is what is called an 'encoder ring', a device that in much the same manner as the selector switch, reports back a varying voltage that tells the TCCM where the transfer case shift motor is presently. When this reported voltage agrees with the desired location the TCCM deems the shift successful and turns the indicator light solid.

Below is a link to a video I just made where I display the selector switch, and 2 multimeters displaying the voltages returned from the selector switch, seen on the red meter on the right, and secondly the encoder ring return voltage indicating shift motor position on the orange meter seen on the left.

The averaged voltages I have observed from the encoder ring are as follows;

2HI = 2.75
A4WD = 3.15
4HI = 3.84
4LO = 0.77
Neutral = 1.6

  1. DISCLAIMER! I cannot recommend anyone try to duplicate what I am doing in the video, that is backprobe 2 adjacent terminals on the TCCM. It is not easy to access and the risk of crossing 2 circuits is great. I won't be doing this again! One circuit at a time yes, but not two.
 

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2003 chevy trailblazer_lt
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28 Posts
If you never even get a flashing 4lo light I would look first at the selector switch. Some reccomend turning that switch back and forth with the key off in an attempt to clean the contacts inside. It sometimes works. I took mine apart and cleaned it out once.

View attachment 55066
with mine when I turn it to 4 low the 4 hi is lit up and 4 low just blinks ? Ive never used 4 low before
 

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2002 chevy trailblazer_lt
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174 Posts
The manual states the optimal way to shift to 4LO is to be in neutral, rolling slowly like 2 mph. It helps to the gears to get lined up.

Manual says engine must be running but I can shift mine with engine off.

Screenshot_20200119-124442.png
 
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